Agrin and neuregulin, expanding roles and implications for therapeutics

Available online at www.sciencedirect.com

Biotechnology Advances 26 (2008) 187–201www.elsevier.com/locate/biotechadv

Research review paper

Agrin and neuregulin, expanding roles and implications for therapeutics

Stacey Williamsa, Colleen Ryana, Christian Jacobsona,b,⁎

a Department of Biology, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada N2L 3G1b Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Ave West, Waterloo, Ontario, Canada N2L 3G1

Received 15 August 2007; received in revised form 21 November 2007; accepted 21 November 2007Available online 4 December 2007

Abstract

Agrin and neuregulin are broadly expressed molecules that have significant developmental roles. Here we review the diverse temporal andspatial expression patterns and functions of these molecules and the impact that dysregulation may have on a number of disease states. Many knowagrin as a modulator of synaptogenesis and the neuregulins for their prominent role in breast cancer; this review elaborates on many of the otherproposed functions for these molecules both in the nervous system and elsewhere. In several instances we discuss the possible use of agrin,neuregulin and related molecules as therapeutic agents.© 2007 Elsevier Inc. All rights reserved.

Keywords: Agrin; Neuregulin; Synapse formation; Development; Disease

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1872. Agrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

2.1. Beyond the neuromuscular junction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1892.2. Agrin in the central nervous system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1902.3. Agrin in non-neuronal tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

3. Neuregulin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1923.1. New perspectives on Neuregulin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1933.2. Outside of the NMJ: the role of neuregulin in the CNS and additional functions of neuregulin in the PNS . . . . . . . . . 1933.3. Neuregulin in non-neural tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

4. Agrin and neuregulin as therapeutics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

1. Introduction

Agrin and neuregulin (Nrg) are developmentally pleiotropicmolecules that, though extensively studied at neuromuscular

⁎ Corresponding author. Department of Biology, University of Waterloo, 200University Ave West, Waterloo, Ontario, Canada N2L 3G1. Tel.: +1 519 8884567x37534.

E-mail address: [email protected] (C. Jacobson).

0734-9750/$ - see front matter © 2007 Elsevier Inc. All rights reserved.doi:10.1016/j.biotechadv.2007.11.003

junctions (NMJ) as regulators of synaptogenesis, appear to bebroadly expressed during development. At the NMJ both agrinand neuregulin are expressed by neurons innervating skeletalmuscle (Fischbach and Rosen, 1997). At this site theglycoprotein agrin functions to assemble aggregations ofmolecules, including acetylcholine receptors (AChR), forefficient transmission of signals across this neuromuscularsynapse (McMahan, 1990; Meier et al., 1997), while it appearsneuregulin acts at these same synapses by upregulating specific

mailto:[email protected]

http://dx.doi.org/10.1016/j.biotechadv.2007.11.003

188 S. Williams et al. / Biotechnology Advances 26 (2008) 187–201

genes at subsynaptic nuclei (Merlie and Sanes, 1985). Recentin vivo findings suggest however, that neuregulin may functionindirectly at the NMJ, perhaps through the support of Schwanncells (Escher et al., 2005; Jessen and Mirsky, 2005). Neurallyderived neuregulin in this interpretation is dispensable topostsynaptic development (Escher et al., 2005; Yang et al.,2001; Jaworski and Burden, 2006).

Essential or not to neuromuscular synapse formation, agrinand neuregulin appear to be developmentally important at othersites. Agrin is expressed in lung, kidney, central and peripheralnervous system, retina, and the immune system and appears tohave varied functions at these sites (Groffen et al., 1998; Halfteret al., 1997; Koulen et al., 1999; Serpinskaya et al., 1999; Khanet al., 2001). Similarly, neuregulin has been implicated innumerous developmental processes. The neuregulins appear tobe involved in lung, muscle, mammary, neuronal, glial, andcardiac development (Fischbach and Rosen, 1997; Peles andYarden, 1993; Patel et al., 2000; Burden and Yarden, 1997; Kimet al., 1999; Burden, 1993; Jacobson et al., 2004; Hippenmeyeret al., 2002). Not surprisingly, both molecules have beenimplicated in the etiology of disease. Agrin and Nrg expressionmay impact diseases of the nervous system includingAlzheimer's disease (Verbeek et al., 1999; Chaudhury et al.,2003) multiple sclerosis (Cannella et al., 1999; Viehover et al.,2001), Parkinson's disease (Liu et al., 2005; Hilgenberg et al.,2006) and schizophrenia (Stefansson et al., 2004) as well asplay prominent roles in cancer (Slamon et al., 1987; Bergeret al., 1988; Tatrai et al., 2006; Rascher et al., 2002; Warth et al.,2004 and others). Recent evidence also suggests that agrin mayalso play an important role in immune (dys)function (Khanet al., 2001) and HIV infection (Alfsen et al., 2005).

2. Agrin

Agrin is a heparin sulfate proteoglycan (HSPG) with a coreprotein size of approximately 220 kDa (Tsen et al., 1995a).Contained within this core protein are several motifs common toother proteins: there are nine Kazal type protease inhibitordomains, three laminin G like domains, and four epidermalgrowth factor domains (Rupp et al., 1991; Tsim et al., 1992;Burgess et al., 2000). The protein also contains several sites for N-and O-linked glycosylation within the N-terminal portion. Theutilization of these sites results in a proteoglycan with a molecularmass typically in excess of 400 kDa (Tsen et al., 1995b; Denzer etal., 1995). The N-terminus also contains two alternative start sites,producing two N-terminal isoforms, which are distinct in bothsequence and functional localization (Burgess et al., 2000). It ishowever, the C-terminus of agrin that is responsible for much ofits biological activity at neuromuscular synapses. In particular, the45 kDa C-terminal is the minimal fragment that can aggregateacetylcholine receptors (AChRs) as well as other post-synapticmolecules to NMJs (Hoch et al., 1994). At the C-terminal of agrinthere are two or three sites for alternative splicing denotedA andBin chicken or X, Y, and Z in rat. (Ferns et al., 1992; Ruegg et al.,1992). The X site appears to have no effect on agrin function(Ferns et al., 1993) and is absent in chicken (Ruegg et al., 1992).The A (or corresponding Y site) binds heparin while it is the

B (orZ) site that is pivotal to agrin's aggregating activity. An insertof 11 amino acids at this site increases aggregating activity by over1000 fold (Burgess et al., 1999; Gesemann et al., 1995). Isoformscontaining the highly active Z site are exclusively expressed bymotor neurons and are thus referred to as neural agrin (Hoch et al.,1994; Ferns et al., 1993; Burgess et al., 1999; Gesemann et al.,1995). Motor neurons secrete neural agrin at their pre-synapticterminals where it binds to the surrounding basal lamina (Denzeret al., 1997) and functions to aggregate AChRs and other synapsespecific molecules on the postsynaptic muscle cell surfaceopposite to the innervating neuron (Nitkin et al., 1987) (Fig. 1,top). The muscle itself expresses a second isoform of agrin, onethat lacks inserts at the Y and Z sites (or the equivalent A and Bsites). The function of muscle agrin remains unclear.

Agrin has been primarily studied as an AChR aggregatingfactor at the neuromuscular junction (NMJ) and although theentire process of AChR clustering has yet to be fully elucidated,significant insights into the role of agrin and its interactionshave been made. There appear to be two receptors for agrin. Thefirst is a cell surface proteoglycan, α-dystroglycan (Ervasti et al.,1990; Yoshida and Ozawa, 1990; Campbell and Kahl, 1989; Geeet al., 1994; Campanelli et al., 1994; Bowe et al., 1994) and thesecond a receptor tyrosine kinase referred to as MUscle Specifictyrosine Kinase, or MuSK (DeChiara et al., 1996; Valenzuela etal., 1995). It is MuSK that is required to induce agrin-dependantsynaptogenesis (Glass et al., 1996a). Agrin induces MuSKphosphorylation and a functional MuSK kinase domain isrequired for the subsequent clustering of AChRs and othersynaptic molecules (Glass et al., 1996b). Agrin however, does notappear to bind directly to MuSK. It presumably binds to putativeco-receptor called MASC, for myotube associated specificitycomponent (Glass et al., 1996a). α-Dystroglycan is not MASCbut it does, none-the-less appear to play an important role inbinding agrin (and synaptogenesis) at neuromuscular synapses aswell as elsewhere during development (Jacobson et al., 1998,2001; Cote et al., 1997, 1999).

Dystroglycan is a central component of the dystrophinglycoprotein complex (DGC)where it is expressed in conjunctionwith a number of other molecules including, the syntrophins, thesarcoglycans, the dystrobrevins and sarcospan (Yoshida andOzawa, 1990; Campbell and Kahl, 1989; Ehmsen et al., 2002).Found in a variety of tissues, the DGC plays critical role inmaintaining membrane integrity (Deconinck and Dan, 2007;Durbeej and Campbell, 2002; Staub and Rotin, 1997, others), intransmembane signaling (Spence et al., 2004) and in theregulation of ion transport (Haenggi et al., 2005; Haenggi andFritschy, 2006). Coded by theDAG1 gene, the dystroglycan geneproduct is post-translationally cleaved to produce two glycopro-tein subunits, α- and β-dystroglycan (Ibraghimov-Beskrovnayaet al., 1992). These subunits span the plasma membrane andprovide structural link between the cytoskeleton and extracellularmatrix binding to laminin (Ervasti and Campbell, 1993), agrin(Gee et al., 1994; Campanelli et al., 1994; Bowe et al., 1994), andthe neurexins (Sugita et al., 2001). Due to their localization andfunction, deficiencies or mutations to the DGC components andassociated basal laminal molecules can result in any number ofmuscular dystrophies (Lovering et al., 2005, others).

Fig. 1. A diagramatic representation of the roles of agrin andNrg at the neuromuscular junction (NMJ). Agrin (top) andNrg (middle) are released by innervating neuronsinto the synaptic space opposite target myofibers. Thesemolecules then bind to their respective receptors on the postsynaptic muscle initiating a phosphorylation cascadethat ultimately results in the reorganization of the postsynaptic membrane and initiation of specific transcription. Agrin induced aggregation of acetylcholine receptors(AChRs) is shown at the top of this figure. The phosphotyrosylation of the MuSK/MASC agrin receptor initiates a signaling cascade that ultimately results in AChRphosphorylation and clustering (McMahan, 1990; Glass et al., 1996b). AChRs are thus localized to areas where the neurotransmitter acetylcholine can induce muscleactivity. In the center panel we can see Nrg binding to the Erb receptors on the muscle surface. This binding can transduce NMJ specific transcription from nucleiproximal to site of the synapse. In this instance we show the transcriptional upregulation AChRs and the subsequent insertion of these receptors into the synapse (1others). Finally, a new junctional paradigm is shown at the bottom of this figure. In it agrin is responsible for both aggregation and transcriptional regulation at synapses.Nrg, in this instance, is believed to have an indirect role in postsynaptic differentiation via proximal Schwann cells (Kummer et al., 2006).

189S. Williams et al. / Biotechnology Advances 26 (2008) 187–201

Dystroglycan, agrin and MuSK are however, not associated withdisease probably due to the lethality of the mutation. In mice,ablation of any one of these molecules has proven to beembryonic lethal (DeChiara et al., 1996; Cote et al., 1997; Henryand Campbell, 1998; Gautam et al., 1996).

2.1. Beyond the neuromuscular junction

Agrin is extensively expressed throughout development anddifferentiation (Groffen et al., 1998; Tsim et al., 1992;Gesemann et al., 1998; Kroger, 1997; Raats et al., 1998).


With recent evidence indicating that agrin plays a role at thecentral nervous system (CNS) both in the brain and spinal cord(Hilgenberg et al., 2006; Hilgenberg and Smith, 2004;McCroskery et al., 2006; Annies et al., 2006; Tournell et al.,2006; Gingras et al., 2002; Gingras and Ferns, 2001), in liverand retina (Groffen et al., 1998; Gesemann et al., 1998; Kroger,1997; Raats et al., 1998; Fuerst et al., 2007), at immunologicalsynapses (Khan et al., 2001; Bezakova and Ruegg, 2003), inlung and kidney (Groffen et al., 1998), in sperm (Kumar et al.,2006), in Alzheimer's disease (Peck and Stopa, 2002; vanHorssen et al., 2002; Berzin et al., 2000; Cotman et al., 2000)and HIV infection (Alfsen et al., 2005).

2.2. Agrin in the central nervous system

Within the central nervous system (CNS) agrin is expressedby all neurons and glia with the highest levels coinciding withsynaptogenesis in the brain (Hoch et al., 1993; O'Connor et al.,1994). Axonal and dendritic extensions, guidance and synapseformation all appear to be regulated by agrin expression(McCroskery et al., 2006; Annies et al., 2006; Kim et al., 2007).Evidence also suggests that agrin alone or in combination withMuSK can act as a stop signal for neurite outgrowth or asguidance cues for developing nerves (Bixby et al., 2002;Campagna et al., 1995; Dimitropoulou and Bixby, 2005; Xu etal., 2005b). MuSK is also expressed in the CNS by bothneuronal and non-neuronal tissues (Smith and Hilgenberg,2002; Garcia-Osta et al., 2006), where presumably it canmediate agrin signaling, not unlike at the neuromuscularjunction. Extrasynaptically, agrin expression appears significantin the maintenance of the blood brain barrier, since the onset ofexpression coincides with the establishment of blood brainbarrier function (Rascher et al., 2002) (see Table 1, top).

Given the extent of agrin expression it might be expected thatagrin ablation in mice would result in profound developmentaldisruptions. Actual results have, however, been mixed. Thebrains of agrin null mice are smaller, but they appear to bestructurally andmorphologically indistinguishable from those ofwild-type littermate controls (Serpinskaya et al., 1999). At thecellular level, synapse formation in cultured wild-type hippo-campal neurons appears to be disrupted by agrin specificantibodies or antisense oligonucleotides (Bose et al., 2000;Ferreira, 1999), but hippocampal neurons isolated from agrinnull animals appear to maintain typical glutamatergic andGABAergic synapses both in vivo and in vitro (Serpinskaya etal., 1999). Furthermore, the disruption of MuSK, the functionalagrin receptor at the NMJ, in hippocampal neurons appears toimpair memory (Garcia-Osta et al., 2006). Obviously there arediscrepancies in the aforementioned results, but on whole the invitro and in vivo results imply a functional role for agrin inhippocampal neuron synaptogenesis.

Cholinergic neurons are found throughout the brain and spinalcord and although the acetylcholine receptors on these neuronsare distinct from those at the neuromuscular junction there is someevidence for the involvement of agrin in the organization of thesecentral synapses as well. For instance, agrin is highly expressedwithin the superior cervical ganglia (SCG) and co-localizes with

postsynaptic cholinergic aggregates in vitro (Gingras and Ferns,2001). Moreover, in cultures of agrin null SCG neurons there is asignificant decrease in synapses compared to wild-type SCGcultures. The SCG synapses in agrin null animals displayedmarked mismatching of pre- and post-synaptic markers anddefective synaptic transmission (Gingras et al., 2002). Combined,this data suggests that agrin expression is critical to theorganization of synapses between cholinergic preganglionicaxons and sympathetic neurons at least in the SCG.

In the brain, agrin co-localizes with, and binds to, the α3subunit of the Na+/K+-ATPase (α3NKA) channel expressed oncortical neurons (Hilgenberg et al., 2006). At these synapses agrinappears to modulate neuronal activity by inhibiting α3NKAchannels (Hilgenberg et al., 2006). In this vein, a reduction inagrin causes a subsequent increase in α3NKA activity. Thisincrease appears to be neuro-protective (Hilgenberg et al., 2002).As might be expected, the loss of the α3NKA channel has beenlinked to increased excitotoxic injury and neural death (Brines etal., 1995; Xiao et al., 2002). For instance, mutations to α3NKAhave been shown be associated with rapid-onset dystoniaParkinson's disease (de Carvalho Aguiar et al., 2004). Thebalance ofα3NKAand agrin expression could thus have dramaticeffects on brain function. The overexpression of agrinmay also beproblematic. Agrin is associated with amyloid plaques inAlzheimer's disease (Verbeek et al., 1999) and Lewy bodiesfound in Parkinson's disease (Liu et al., 2005). In Alzheimer'sdisease, agrin appears to bind fibrillar β-amyloid protecting β-amyloid from proteolysis while concomitantly altering its ownsolubility (Cotman et al., 2000). In the brain, agrin appears notonly to be inhibitory to neuro-protective ion channels but mayalso be a structural component of senile plaques; an increase inagrin expression can potentially exacerbate the Alzheimer'sdisease state via these two mechanisms.

2.3. Agrin in non-neuronal tissues

In the lungs and kidneys agrin expression appears highest inthe alveolar and glomerular basement membranes, respectively(Groffen et al., 1998); where it may be involved in the membranepermeability and filtration (Groffen et al., 1999). In the kidney,agrin is a predominant heparin sulfate proteoglycan in theglomerular basement membrane (Raats et al., 2000). Decreases inexpression of agrin appear to be key to the formation of minimalchange nephritic syndrome, a disease in children linked to areduction of heparin sulfate in the glomerular basementmembrane, (Groffen et al., 1999) and possibly overt diabeticnephropathy (van den Hoven et al., 2006). Several lines ofevidence also suggest that agrin acts as a protease inhibitor in lungtissue (Biroc et al., 1993; van de Lest et al., 1995). In the lungs,this activity may balance protease activity thereby maintainingnormal function. It is the disruption of the protease-anti-proteasebalance that may be pivotal in the pathogenesis of emphysema(reviewed in Gadek and Pacht, 1990). Experimentally, this can beseen in rat lung treated with pancreatic elastase. There is adramatic decrease in heparin sulfate proteoglycans and the deve-lopment of experimental pulmonary emphysema (van de Lestet al., 1995) (Table 2 top).

Table 1Selected proposed functions of agrin and neuregulin in the nervous system

Protein Location Organ/cell type Effect Reference(s)

AgrinPNS α1 and γ1 motor

neuron synapsesInduction of neuromuscularjunction synaptogensis

(McMahan, 1990; Ferns et al., 1992;Gautam et al., 1996)

CNS Brain and Spinal cord;Miscellaneous cells.

Axonal and dendritic extension,guidance, synapse formation.Stop signal for outgrowth

(McCroskery et al., 2006; Annies et al.,2006; Kim et al., 2007; Dimitropoulou and Bixby,2005; Xu et al., 2005b)

Brain and spinal cord;blood brain barrier.

Potential role in maintainingblood-brain barrier

(Rascher et al., 2002; Warth et al., 2004)

Brain; hippocampal neurons Uncertain, potential for role inhippocampal neuron synaptogenesis,memory

(Serpinskaya et al., 1999; Garcia-Osta et al.,2006; Bose et al., 2000; Ferreira, 1999)

Brain; cortical neurons Binds to Na+/K+-ATPase, roleuncertain, potential effects onneuroprotection

(Hilgenberg et al., 2006, 2002)

Spinal cord; superiorcervical ganglia (SCG)

Organization of synapses (Gingras et al., 2002; Gingras and Ferns, 2001)

NeuregulinPNS Schwann cells Survival, myelination, proliferation,

migration, differentiation(Marchionni et al., 1993; Shah et al., 1994;Dong et al., 1995; Mahanthappa et al., 1996;Garratt et al., 2000; Chen et al., 2006)

α1 and γ1 motor neuronsynapses

Up-regulation of AChR (Fischbach and Rosen, 1997;Merlie and Sanes, 1985)

Peripheral nerves Fasiculation, survival (Wolpowitz et al., 2000)Proprioceptive synapses Neuregulin signaling initiates muscle

spindle fiber differentiation(Jacobson et al., 2004; Hippenmeyer et al., 2002)

CNS Oligodendrocytes Survival, myelination, proliferation,differentiation

(Park et al., 2001; Calaora et al., 2001;Canoll et al., 1996; Flores et al., 2000)

General neurons Survival, differentiation and migration (Erickson et al., 1997; Bermingham-McDonogh et al.,1996; Anton et al., 1997; Rio et al., 1997)

General synapses Neurotransmitter receptor (nicotinicAChRs, GABA and NMDA receptors)regulation

(Ozaki et al., 1997; Yang et al., 1998;Liu et al., 2001; Rieff et al., 1999)

Cranial nerves Fasciculation (Meyer and Birchmeier, 1995; Erickson et al.,1997; Kramer et al., 1996)

Hypothalamus Mammalian female sexual maturation (Ma et al., 1999; Prevot et al., 2003)Cerebellum Generation of cerebellar neural precursors (Erickson et al., 1997)


In cancer, the aberrant expression of heparin sulfateproteoglycans (HSPGs) has been associated with increasedtumorgenesis and metastasis (reviewed in Sanderson et al.,2005; Sasisekharan et al., 2002). Agrin, in particular has beencited as a factor in cirrhosis of the liver and hepatocellularcarcinoma (Tatrai et al., 2006). In these instances agrin appearsto play a potential role in the vascularization of tumors and inbile ductile proliferation (Tatrai et al., 2006). In glioblastomamultiforme (GBM), a highly malignant form of brain cancerwith high morbidity, there is an upregulation of tenascin, amolecule that activates angiogenesis, migration and prolifera-tion of cells during neoplasia, and a subsequent decrease in theexpression of agrin (Rascher et al., 2002;Warth et al., 2004). Thedecrease of agrin in GBM presumably disrupts the integrity ofthe blood-brain barrier and may thus contribute to the severity ofthis cancer. Agrin may also serve as a trigger for the proliferationin osteosarcoma. Chondrocytes are critical to the formation ofvertebrae, pelvis, ribs and long bones via endochondralossification. These cells are highly organized and can becharacterized as resting, proliferating or hypertrophic cells withall forms residing within the cartilaginous growth plate regionsat the distal ends of the developing bones. In agrin knock out

mice, there is a dramatic decrease in the prominence ofhypertrophic chondrocytes as well as substantial changes tothe cartilage-specific extracellular matrix (Hausser et al., 2007).It is possible that the overexpression of agrin in osteosarcomacan drive the aberrant proliferation of cells. In support of this,agrin isolated from the extracellular matrix components ofEngelbreth-hom-Swarm (EHS) sarcoma tumors stimulated thegrowth and migration of an osteosarcoma cell line to the greatestdegree (Harisi et al., 2005).

Proteins originally isolated from the nervous system can alsobe found in the immune system. It is no surprise therefore thatthere is new evidence showing that agrin is expressed in T-cells(Khan et al., 2001). Fabio Rupp's group (2001) demonstrated thatagrin is present in both resting and activated lymphocytes and thatit is capable of inducing T cell receptor (TCR) clustering. Theclustering of TCRs and other immunological synapse (IS)molecules is vital to the activation of the T cells and the properprogression of an immune response (Dustin, 2002; Gascoigne andZal, 2004; Jacobelli et al., 2004). Agrin at the IS has shown someinteresting features not seen in other tissues. Activity appearsdependent on deglycosylation as opposed to a specific splicevariant. It appears that glycosylated agrin is dominant in resting

Table 2Selected proposed functions of agrin and neuregulin outside of the nervous system

Protein Organ/cell type Effect Reference(s)

AgrinLung Membrane permeability, filtration (Groffen et al., 1998, 1999, 1997)Kidney Membrane permeability, filtration (Groffen et al., 1998, 1999, 1997;

Raats et al., 1998, 1999)Retina Ocular dysgenesis (Fuerst et al., 2007)Bone Regulation of chondrocyte development (Hausser et al., 2007)Immune system Induction of T-cell receptor clustering (Khan et al., 2001)Central nervous system Integrity of the Blood-Brain barrier (Rascher et al., 2002)

NeuregulinMuscle Myogenesis, glucose uptake and cell survival (Trachtenberg and Thompson, 1996;

Suarez et al., 2001; Kim and Huganir, 1999)Lung Increased lung epithelial cell proliferation and

volume density during lung organogenesis, Brachialbranching, Possibly involved in surfactant synthesis

(Patel et al., 2000; Dammann et al., 2003;Liu et al., 2004)

Breast Promotes mammary epithelial proliferation andmorphogenesis and is involved in lobuloalveolardevelopment during pregnancy

(Li et al., 2002; Yang et al., 1995)

Heart Involved in myocardial cell outgrowth leading toformation of the trabeculae, valve formation,development of the cardiac conduction system

(Meyer and Birchmeier, 1995; Erickson et al., 1997;Lee et al., 1995; Gassmann et al., 1995)(Rentschler et al., 2002)

Stomach Gastric epithelial cell proliferation (Noguchi et al., 1999)Uterus Embryo-uterine interactions during implantation (Brown et al., 2004)Gonads Growth and survival of primordial germ cells (Toyoda-Ohno et al., 1999)


lymphocytes and deglycosylation is coincident with lymphocyteactivation. This discovery also leads to a wide variety of researchpossibilities. The mechanism of action, including the trigger foragrin deglycosylation as well as the mode of action, has yet to bedetermined; and there is no research pointing to immuneconditions to which agrin may be associated. However, it isplausible that agrin is necessary for immune cell activation, andtherefore,may be involved in autoimmune disorders and allergies.Finally, Alfsen et al. (2005) have reported that agrin may play animportant role in HIV infection (Alfsen et al., 2005). In thisinstance, agrin potentially acts as an HIV-1 attachment receptorduring transcytosis between infected cells and mucosal epithelialcells (Alfsen et al., 2005). Agrin is, in effect, assisting andaugmenting HIV infectivity.

3. Neuregulin

The neuregulins are a family of glycoproteins that activateErbB family receptor tyrosine kinases to mediate the prolifera-tion, differentiation, migration and survival of a number of celltypes (Buonanno and Fischbach, 2001). In the motor neuron-muscle system, Nrg has been implicated in the maturation of thepostsynaptic membrane at the neuromuscular junction (Jo et al.,1995), the survival of Schwann cell precursors (Trachtenbergand Thompson, 1996), the maturation of Schwann cells inperipheral nerves (Kopp et al., 1997), in glucose metabolism(Suarez et al., 2001), myogenesis (Kim et al., 1999) and musclespindle formation (Jacobson et al., 2004; Hippenmeyer et al.,2002). Nrg expression and function are not however, restricted tothe peripheral nervous system. Within the central nervoussystem (CNS) Nrg and the ErbB receptors appear to regulate theexpression of the N-methyl-D-aspartate (NMDA) glutamate

receptor (Ozaki et al., 1997; Gu et al., 2005) and potentially mayplay a role in schizophrenia (Stefansson et al., 2002) (See Table1, bottom).

Prior to the implementation of a consistent system ofnomenclature the Nrgs were known as acetylcholine receptor-inducing activity (ARIA), heregulin (HRG), sensorimotor-derived factor (SMDF), neu differentiation factor (NDF) orglial growth factor (GGF) (Fischbach and Rosen, 1997; Pelesand Yarden, 1993; Burden and Yarden, 1997). The diversenames reflected the numerous functions and isoforms of thegene and the circumstances in which these proteins wereisolated. For instance, in 1992, Holmes et al. and Peles et al.described HRG and NDF as ligands for the oncogene ErbB2,respectively (Holmes et al., 1992; Peles et al., 1992). Earlier,ARIA had been described by its ability to increase expression ofacetylcholine receptors in skeletal muscle (Fischbach andRosen, 1997; Jessell et al., 1979; Usdin and Fischbach, 1986).The glial growth factors (GGFs) were isolated from bovinepituitary gland extracts and were shown to induce highmitogenic activity in Schwann cells (Raff et al., 1978;Marchionni et al., 1993; Goodearl et al., 1993) as well asbeing ligands for the ErbB2 receptor (Marchionni et al., 1993).Finally, in 1995, Ho and others isolated yet another isoform ofthe Nrgs, SMDF, which is highly expressed in sensory andmotor neurons and appears to be expressed primarily within thenervous system (Ho et al., 1995). All of the above, ARIA, GGF,HRG, NDF and SMDF are all gene products of the NRG1 gene.Presently, there are over fifteen known isoforms of the genegenerated by extensive alternative splicing (Peles and Yarden,1993; Ben-Baruch and Yarden, 1994). These alternativelyspliced products all share the conserved epidermal growthfactor (EGF) domain and are broken down into three different


sub types: type I which includes NDF, ARIA and HRG; type IIincluding GGF; and finally, SMDF, is an example of a type IIINrg. Two additional domains define in part, the various iso-types. Type I and II isotypes contain an immunoglobulin-like(Ig-Nrg) domain while type III Nrgs have a cysteine-richdomain (CRD-Nrg). Presently, there are four genes known thatcode for Nrgs. In addition to NRG1, the genes NRG2, -3 and -4code for proteins of similar structures and features (Carraway etal., 1997; Zhang et al., 1997; Harari et al., 1999). Theseadditional genes, their products and roles, will however, not bediscussed here due to space constraints and the limitedinformation available about their activities. Some discussionof these genes can be found in Falls (Falls, 2003) and Britsch(Britsch, 2007).

Nrg signals through homo- and heterodimers of the ErbBreceptors. Nrg1 is capable of binding directly to ErbB3 andErbB4 (Fischbach and Rosen, 1997). Although ErbB3 demon-strates high affinity binding to Nrg1, it cannot autopho-sphorylate in response to Nrg, which is necessary for signaltransduction, and it therefore forms functional heterodimerswith ErbB2 and ErbB4 (Burden and Yarden, 1997; Lemke,1996). ErbB2 also forms heterodimers by necessity, as it isincapable of directly binding to any of the Nrg isoforms, ithowever, exhibits strong kinase activity (Lemke, 1996). TheErbB2–ErbB3 heterodimer is the most potent activator of theRas–Erk pathway leading to proliferation and differentiation, aswell as the phosphatidylinositol-3-kinase (PI3K)-Atk survivalpathway)(Altiok et al., 1997; Tansey et al., 1996).

3.1. New perspectives on Neuregulin

Recent publications have spurred conflicting theories as tothe role of Nrg in synaptogenesis at the NMJ. So much so, thatKummer and colleagues (2006) have published a reviewchallenging the conventional and generally accepted paradigmthat Nrg directly regulates gene transcription at the NMJ (Fig.1, center) (Kummer et al., 2006). Accumulating evidenceinstead suggests that Nrg may act indirectly. Generation oftransgenic mice that lack motor neurons nevertheless exhibitAChR clustering in the mid-section of the muscle (Yang et al.,2001). The cluster patterning of the AChRs is also observed inthe absence of a source of Nrg, prior to sensory and/orautonomic axons reaching the muscle (Yang et al., 2001). Cre-lox conditional ablation of erbB2 and erbB4 genes in skeletalmuscle, results in mice that are only mildly affected by the lackof Nrg receptors in muscle (Escher et al., 2005). Furthermore, itappears that neural agrin can induce the differentiation and theexpression of AChRɛ, thereby making the synapse-specificinduction of transcription by Nrg redundant (Escher et al.,2005). Additional studies of transgenic mice have beenpreformed where NRG1 is selectively inactivated in developingmotor neurons, skeletal muscle or in both cell types (Jaworskiand Burden, 2006). Transgenic mice with NRG1 selectivelyinactivated in these cell types alone and inactive in both motorneurons and skeletal muscle together, demonstrate the typicalclustering of AChRs at the synapse and the characteristicsynapse-specific transcription (Jaworski and Burden, 2006). It

this study Agrin/MuSK signaling remains and as such isbelieved to mediate AChR clustering and the induction ofsynapse-specific gene expression. Jaworski and Burden (2006)thus assume that the action of Nrg in this process may beexpendable (Jaworski and Burden, 2006). In this model, shownin Fig. 1 at the bottom, Nrg at NMJ synapse has been assignedan indirect role; primarily as a growth and survival signal toSchwann cells (Escher et al., 2005). It is these cells that may, inturn, provide support signals to neurons and aid in themaintenance of the synapse (Davies and Wright, 1995;Black, 1999). It appears a new paradigm for Nrg at the NMJis promptly being created, wherein Nrg has an indirect, ratherthan direct, role in synapse formation (Kummer et al., 2006).

3.2. Outside of the NMJ: the role of neuregulin in the CNS andadditional functions of neuregulin in the PNS

Although Nrg may not play an essential role in thedevelopment of a stable synapse for efficient transmission ofsignals at the NMJ, it does have significant roles in the nervoussystem. For instance, Nrg is integral to cell survival, migrationand differentiation of neurons and glial cells (Fischbach andRosen, 1997; Peles and Yarden, 1993; Burden and Yarden,1997), and is now known to play an important role in musclespindle development (Hippenmeyer et al., 2002). Nrg is alsoexpressed and plays roles in the CNS and may contribute to anumber of nervous system disease states (Chaudhury et al.,2003; Cannella et al., 1999; Viehover et al., 2001; Liu et al.,2005; Stefansson et al., 2004).

Outside of the NMJ, Nrg secreted by group 1a sensoryafferent neurons provide the necessary signal to developingmuscle to differentiate into the highly specialized musclespindle fibers, which are involved in proprioception (Hippen-meyer et al., 2002). The Nrg provided by the sensory neuroninduces the transcription factor early growth response factor 3(Egr3) (Jacobson et al., 2004), which is essential for musclespindle fiber development (Tourtellotte and Milbrandt, 1998)(Table 1, bottom).

In vitro and in vivo experiments have shown Nrg signaling isinvolved in the early development of myelin producing cellsand neurons of the PNS and CNS (Shah et al., 1994; Vartanianet al., 1994; Dong et al., 1995; Meyer and Birchmeier, 1995).Early studies report Nrg (GGF) promotes the differentiation ofneural crest cells to glial lineages, while also suppressingneuronal differentiation (Shah et al., 1994). In Schwann cells, ithas been established for quite some time that Nrg (GGF) acts asa powerful mitogen in cultures (Marchionni et al., 1993).Survival, proliferation, migration and maturation of Schwanncell precursors are also regulated by Nrg (Dong et al., 1995;Mahanthappa et al., 1996). Nrg is also involved in myelination(Garratt et al., 2000; Chen et al., 2006), and regulates thethickness of myelin sheaths wrapped around the axon(Michailov et al., 2004). Differentiation, proliferation, myelina-tion and cell survival of oligodendrocytes, the myelin producingcells of the CNS, are also functions of Nrg (Park et al., 2001;Calaora et al., 2001; Canoll et al., 1996; Flores et al., 2000). Inthe absence of Nrg (NRG−/− explants), spinal oligodendrocytes


fail to develop; a phenotype that can be rescued by the additionof recombinant Nrg (Vartanian et al., 1999). Due to theimportant role Nrg plays in the development and survival ofoligodendrocytes, research has looked at a possible role for Nrgin the demyelinating autoimmune disease multiple sclerosis(MS), as well as possible Nrg mediated therapies (Viehover et al.,2001; Cannella et al., 1998). Addition of Nrg to mice withexperimental autoimmune encephalomyelitis (EAE), the mousemodel of the human disease MS, results in a marked decrease inseverity of disease, delay of symptom onset and reduction in therate of relapse (Cannella et al., 1998).

Nrg is highly expressed in the brain during development andcontinues to be expressed in the adult brain (Chaudhury et al.,2003; Holmes et al., 1992; Chen et al., 1994; Ozaki et al., 2000;Law et al., 2004). During development, Nrg is involved in theformation of CNS synapses, generation of cerebellar neuralprecursors and the proliferation, differentiation and migration ofneurons (Yang et al., 1998; Erickson et al., 1997; Bermingham-McDonogh et al., 1996; Anton et al., 1997; Rio et al., 1997).Nrg also acts to mediate fasciculation of both cranial andperipheral nerves (Meyer and Birchmeier, 1995; Erickson et al.,1997; Wolpowitz et al., 2000; Kramer et al., 1996). In themature brain, Nrg is involved in hypothalamic controlled femalesexual development (Ma et al., 1999; Prevot et al., 2003). In thehypothalamus, Nrg signals via ErbB2–ErbB4 heterodimer onhypothalamic astrocytes, which in turn produce the prostaglan-din E2, stimulating the production of luteinizing hormone-releasing hormone (LHRH) and signaling the pituitary to beginrelease of puberty specific hormones (Prevot et al., 2003). Thisneuron-glial communication signals the advent of puberty inmammalian females.

Although Nrg appears to mediate many diverse functions inthe nervous system, of current interest is the involvement of Nrgin disease, particularly schizophrenia. A genetic role for Nrg inschizophrenia was initially implied by the location of the NRG1gene near the 8p12–p21 schizophrenia susceptibility loci(Blouin et al., 1998). Linkage and haplotype analysis thenlater identified an at risk NRG1 haplotype that is coincidentwith schizophrenia in several populations (Stefansson et al.,2002; Stefansson et al., 2003). Recently, the ErbB4 Nrg receptorhas also been associated with schizophrenia (Silberberg et al.,2006). The linkage of Nrg to schizophrenia and the regulation ofglutamate (NMDA) receptor expression by Nrg (Ozaki et al.,1997; Gu et al., 2005) leads to the question, how does Nrgregulate NMDA expression in the brain and are there otherchanges effected by reduced Nrg in schizophrenic individuals?Nrg is capable of regulating the expression of differentneurotransmitter receptor subunits including hippocampal nico-tinic AChR subunits, NMDA-receptor subunits and GABAA

receptor subunits (Ozaki et al., 1997; Gu et al., 2005; Yang et al.,1997; Liu et al., 2001; Rieff et al., 1999) with two recentpublications reporting evidence that suggests Nrg-ErbB4 signal-ing regulates synaptic transmission at CNS GABA and glutamatesynapses (Li et al., 2007; Woo et al., 2007). Accumulatingevidence is suggesting that impaired or altered function of GABAand glutamate receptors may be one effector of schizophrenia (Liet al., 2007; Woo et al., 2007; Lewis and Moghaddam, 2006).

3.3. Neuregulin in non-neural tissues

Nrg is involved in a diverse array of developmental processesoutside of the nervous system. These processes include cardiacdevelopment and angiogenesis (Meyer and Birchmeier, 1995),lung development (Patel et al., 2000; Dammann et al., 2003),mammary gland morphogenesis during pregnancy (Li et al.,2002),myogenesis and survival ofmuscle cells (Kim et al., 1999).During development, Nrg is also expressed in the gastro-intestinaltract by gastric fibroblasts and causes increased proliferation ingastric epithelium (Noguchi et al., 1999).More diversely, Nrg hasbeen implicated in signaling in embryo-uterine interactions inmice during implantation (Brown et al., 2004), as well as fetalgonadogenesis (Toyoda-Ohno et al., 1999) (see Table 2, bottom).

Early knockout studies revealed the importance of Nrgsignaling in cardiac development. Nrg null mice die early indevelopment at embryonic day 10.5 (E10.5) due tomalformationsin the developing heart (Meyer and Birchmeier, 1995). Nrg isexpressed in the endocardial endothelium and the receptor ErbB4is expressed in the myocardium, which ultimately gives rise to thetrabecules (Meyer and Birchmeier, 1995). NRG1 knockout micedo not exhibit normal myocardial cell out growth and trabe-culation (Meyer and Birchmeier, 1995). ErbB2 and ErbB4knockoutmice also demonstrate this absence of trabeculae (Lee etal., 1995; Gassmann et al., 1995). Expression of ErbB3 appears tobe confined to the endocardial cushion, which ultimately givesrise to cardiac valves (Meyer and Birchmeier, 1995). The cardiaccushion of ErbB3−/− mutant mice appears thinner and lacksmesenchyme; these mice die at E13.5 (Erickson et al., 1997).Thus, Nrg/ErbB signaling is essential for both trabeculation andvalve formation in the developing heart. Nrg is also theendocardial-derived factor that induces the differentiation ofcardiomyocytes into cardiac conduction cells, which generateelectrical excitation of the heart (Rentschler et al., 2002).

In the developing lungs, the Nrg receptors ErbB2, ErbB3 andErbB4 and Nrg are expressed during the second trimester ofhuman fetal development (Patel et al., 2000). Nrg presumablysignals in an autocrine manner in the developing lungs increasingthe proliferation of pulmonary epithelial cells (Patel et al., 2000).Furthermore, Nrg signaling via the phosphatidylinosital-3-kinase(PI3K) pathway also appears to increase branching morphogen-esis in mice (Liu et al., 2004). Nrg may also signal via amesenchyme-epithelial paracrine mechanism between fetal lungfibroblasts and lung epithelial cells (Dammann et al., 2003). Thisinteraction suggests a role for Nrg in surfactant production, aspurified Nrg mimics the surfactant production inducing effects oflung fibroblast-conditioned medium (Dammann et al., 2003).

As in the lungs, Nrg also exerts proliferative effects on thebreast epithelium during late pregnancy (Li et al., 2002). Invitro, Nrg stimulates mammary epithelial morphogenesissuggesting Nrg may be capable of enhancing lobuloalveolardevelopment as well as stimulating secretory alveoli accumula-tion (Yang et al., 1995). In vivo, NRG1 null mice exhibit defectsin mammary gland lobuloalveolar development in late preg-nancy and early post-partum (Li et al., 2002). Lack of Nrg alsoresults in decreases in β-casein expression and proliferation ofepithelial cells (Li et al., 2002). Understanding the role of Nrg as


a mammary gland mitogen in normal mammary glanddevelopment will improve the understanding of Nrg and itsreceptors in the development of breast cancers.

Abnormal expression of Nrg (HRG) is capable of inducingthe development and growth of mammary tumors as well asmetastasis (Atlas et al., 2003). Gene amplification and increasedprotein expression of the Nrg receptor ErbB2 (also referred to asHER-2) was identified in the late 1980s as a predictor ofsurvival and time to relapse in breast cancer patients (Slamon etal., 1987; Berger et al., 1988). Not surprisingly, ErbB2 copynumber is also an indicator of a tumors susceptibility to certaintherapies (reviewed in Ross and Fletcher, 1998). Simply put,ligand-dependent activation of an excess of ErbB receptors (byNrg) can lead to cancer but strategies exist to specifically targetthis protein.

During fetal development, Nrg also appears to be involved ingonadogenesis (Toyoda-Ohno et al., 1999). Both Nrg and itsreceptors, ErbB2–ErbB3 are expressed in the genital ridges ofdevelopingmice between 11.5 and 13.5 days post coitus (Toyoda-Ohno et al., 1999). Furthermore, addition of recombinant Nrg-βto cultured primordial germ cells resulted in increased cellnumbers indicating this isoform of Nrg may be involved ingrowth and survival of primordial germ cells (Toyoda-Ohno et al.,1999).

More diversely, Nrg appears to have reproductive implica-tions. During implantation, type I and type III Nrg isoforms areexpressed by uterine subepithelial stroma adjacent to theblastocyst (Brown et al., 2004). The blastocyst demonstrated acoincident upregulation of the erbB2 and erbB3 receptor tyrosinekinases (Brown et al., 2004).

4. Agrin and neuregulin as therapeutics

Heregulin/neuregulin was identified for its ability to bindErbB2, which consequently signals, and results in potent cellproliferative effects and is employed by cancer cells to fixoncogenic mutations (Yarden and Sliwkowski, 2001). Over-expression of ErbB2 in breast cancer correlates with highmalignancy and large tumor size (Ross and Fletcher, 1998).This overexpression and gene amplification of ErbB2 is anindicator of disease prognosis, a predictor of survival and apredictor of response to therapeutics (Slamon et al., 1987; Musset al., 1994). Cancer therapeutics target this interaction.Treatment with monoclonal antibodies is highly specific withlow toxicity to unaffected tissues. Trastuzumab (Herceptin®;Genentech, Inc.; South San Francisco, CA), a humanizedantibody against ErbB2, has received clinical approval and actsto down regulate surface ErbB2 in addition to inducing Rb-related protein (p130) and cyclin-dependent kinase inhibitor(p27Kip1). Both act to reduce the number of cells in S-phase(Sliwkowski et al., 1999). Another strategy targeting the ErbB2receptor in breast cancer has been through the use of tyrosinekinase inhibitors. Dual tyrosine kinase inhibitors target both theErbB2 receptor and the EGFR receptor (Rusnak et al., 2001).This tyrosine kinase inhibitor, Lapatinib (GalaxoSmithKline;Research Triangle Park, NC), has been shown to be highlycytotoxic against the growth of breast cancer cells grown in

culture and result in cessation of tumor growth and/or apoptosis(Rusnak et al., 2001; Xia et al., 2002).

Vaccination is yet another approach in breast cancer therapythat also targets the Nrg receptor ErbB2. A successful cancervaccination requires overcoming immune tolerance to self-antigens and the ultimate goal is to elicit a strong immunogenicresponse as well as generate immunological memory to preventreoccurrence. Early studies used peptide fragments of humanErbB2 protein to immunize rats (Disis et al., 1998). Immuniza-tion of the rats with the human intracellular domain of ErbB2resulted in substantial T-cell response (Disis et al., 1998).Preliminary clinical trials were able to generate protein-specificT-cell responses in 6 out of 8 patients immunized with peptidefragments from both the intracellular and extracellular domainof ErbB2 and using granulocyte macrophage-cytokine stimulat-ing factor (GM-CSF) as an adjuvant (Disis et al., 1999). Manydifferent strategies and various peptide-adjuvant combinationshave been explored and are currently being tested in clinicalsettings (Curigliano et al., 2006).

Although Trastuzumab is useful artillery in combating breastcancer, early clinical treatments revealed detrimental conse-quences to the heart following treatment with this anti-ErbB2monoclonal antibody. Cardiac dysfunction was observed in asmall percentage of patients that were treated with Trastuzumabfollowing prior treatmentwith the chemotheraputic anthracycline.When given combined treatment the incidence of cardiacdysfunction increased 3 fold (7% to 28%) (Slamon and Pegram,2001; Baselga, 2000a,b; Sparano, 2001. Conditional deletions ofErbB2 in the ventricle of mice results in mutants that are viable,but develop cardiac dysfunction, comparable to that observed inTrastuzumab treated cancer patients (Crone et al., 2002). Thesemutants not only exhibit dilated cardiomyopathy, but cardiomyo-cytes from the mutant mice were shown to have an increasedsensitivity to the toxic effects of anthracycline (Crone et al.,2002). The importance of Nrg signaling through the ErbB-receptors is well understood as an essential signal for trabecula-tion in the heart during embryonic development (Lee et al., 1995).Cardiomyopathy resulting from Trastuzumab treatment suggestsa critical role for Nrg signaling in the adult heart. Nrg receptorsErbB2 and ErbB4 continue to be expressed in adult myocardium(Zhao et al., 1998). Moreover, Nrg-ErbB signaling in culturedcardiac myocytes recovered from adult rats promotes the survivaland growth of the myocytes and also suppresses apoptoticpathways (Zhao et al., 1998). Blocking initiation of thesepathways with the breast cancer therapy Trastuzumab maydisrupt these functions of Nrg in the heart and could be themechanism that causes the cardiomyopathies observed in cancerpatients.

If decreased Nrg signaling by blocking its receptor results incardiac dysfunction, one must wonder what effect increasedNrg-ErbB-activation may have in states of heart failure. Itappears there is a reduction in the expression of the receptors instates of cardiac failure, while ErbB2 and ErbB4 areupregulated in times of recovery. A decrease in expression ofErbB2 and ErbB4 is observed with the onset of cardiac failure inrats with hypertrophy (Rohrbach et al., 1999), while humanpatients with severe heart failure that have undergone


mechanical unloading, using a left ventricular assist device,demonstrate an upregulation in ErbB2 and ErbB4 and improvedcardiac function (Uray et al., 2002). Investigation of recombi-nant Nrg1 as a therapeutic for heart failure has been explored inanimal models for ischemic, dilated and viral cardiomyopathies(Liu et al., 2006). Results suggest a potentially very potent anduseful therapy for treating heart failure, as treatment withrecombinant Nrg increased survival of cardiomyocytes withimprovement in cardiac function (Liu et al., 2006). Adminis-tration of recombinant Nrg to these rodent models forcardiomyopathy and myocarditis showed attenuation in myocar-dial cell damage (Liu et al., 2006). Prevention of cardiac damagewas observed in rat models for viral- and drug-inducedmyocarditis and cardiomyopathies (Liu et al., 2006). Evendelayed (2 months) treatment with recombinant Nrg results inimprovements in cardiac function and survival in the rat infarctmodel (Liu et al., 2006). Collectively, these results suggest atherapeutic potential for recombinant Nrg in treating patients withheart failure.

The possibilities of Nrg as a therapeutic are not limited tobreast cancer and heart failure. Perhaps in the future it could alsobe used to treat those who have suffered from a stroke. Stroke isone of the major causes of death and the leading cause of long-term disability. Ischemic stroke causes neural loss, but theinflammatory response that follows causes further neuraldestruction by inducing apoptosis (Ferrer and Planas, 2003).Blocking this inflammatory response would provide neuroprotec-tion and limit the amount of neuronal damage. Upregulation ofNrg has been reported following traumatic brain injury and focalstroke (Tokita et al., 2001; Parker et al., 2002). Interestingly, thisincrease in Nrg expression may intervene in focal stroke andprovide neuroprotection by attenuating the induced pro-inflam-matory response and delayed neuronal death (Xu and Ford, 2005).A microarray based comparison of the brains of Nrg treated anduntreated ischemic animals showed a decrease in the expressionof many pro-inflammatory cytokines in the Nrg treated ischemicanimals compared to untreated animals with induced ischemia(Xu et al., 2005a). Studies also suggest Nrg acts not only todownregulate pro-inflammatory cytokines, but also acts to blockmicroglia and macrophage infiltration, astrocyte activation andneural apoptosis (Xu and Ford, 2005; Xu et al., 2005a; Guo et al.,2006). The neuroprotective actions that Nrg provides againstinflammatory responses could provide a potentially effectivemethod to treat stroke patients.

Althought Nrg and manipulation of its receptors may be auseful as therapies in chronic disease states; it is not limited tothem. Nrg is also being explored as a therapy for genetic diseasessuch as Duchenne's muscular dystrophy (DMD). Nrg maybe auseful therapy in DMD due to the ability of Nrg to activate ets-related transcription factors, which subsequently activate theutrophin promoter A (Dennis et al., 1996). This results in theoverexpression of utrophin, which acts to substitute fordystrophin, and has been shown to rescue muscle dystrophin-deficient mdx mutant mice (Tinsley et al., 1996). Agrin has alsobeen investigated as a possible therapeutic in a subgroup ofmuscular dystrophies, the merosin-deficient congenital musculardystrophy (Bentzinger et al., 2005). This specific subgroup of

muscular dystrophies is an autosomal recessive disorder resultingfrommutations in the laminin-α2 (merosin) chain-encoding gene.The dyw/dyw and dy3k/dy3k mutant mice have targeted deletion tothe lama2 gene and serve as mouse models for this disease(Kuang et al., 1998; Miyagoe et al., 1997). Treatment of dyw/dyw

and dy3k/dy3k mice with an agrin mini-gene was shown tocounteract the disease and rescue dystrophic symptoms (Bent-zinger et al., 2005; Moll et al., 2001). Further findings into rolesfor Nrg and agrin in development and disease will undoubtedlyresult in potential new therapies to combat those very disorders.

Although agrin and Nrg have been extensively studied forthe better part of two decades, there are still significantquestions that remain to be answered. For instance, there arestill several molecules implied in the Agrin/MuSK signalinghypothesis. Furthermore, while the broad strokes of synapto-genesis are known, additional roles for agrin and Nrg in thedevelopment of the NMJ are still being determined. Agrin andNrg are involved in an array of developmental processes andperhaps a better understanding of these roles will lead toinsights at the NMJ as well as their roles in the etiology ofdisease. From there they may provide avenues to therapies tocombat these illnesses.

Acknowledgements

The authors like to thank Malwina Mencel for her inputthroughout the writing and editing of this manuscript. S.W. issupported by anOntario Graduate Scholarship. C. J. would like tothank NSERC for continued support.

References

Alfsen A, Yu H, Magerus-Chatinet A, Schmitt A, Bomsel M. HIV-1-infectedblood mononuclear cells form an integrin- and agrin-dependent viralsynapse to induce efficient HIV-1 transcytosis across epithelial cellmonolayer. Mol Biol Cell 2005;16:4267–79.

Altiok N, Altiok S, Changeux JP. Heregulin-stimulated acetylcholine receptorgene expression in muscle: requirement for MAP kinase and evidence for aparallel inhibitory pathway independent of electrical activity. EMBO J1997;16:717–25.

Annies M, Bittcher G, Ramseger R, Loschinger J, Woll S, Porten E, et al.Clustering transmembrane-agrin induces filopodia-like processes on axons anddendrites. Mol Cell Neurosci 2006;31:515–24.

Anton ES, Marchionni MA, Lee KF, Rakic P. Role of GGF/neuregulin signalingin interactions between migrating neurons and radial glia in the developingcerebral cortex. Development 1997;124:3501–10.

Atlas E, Cardillo M, Mehmi I, Zahedkargaran H, Tang C, Lupu R. Heregulin issufficient for the promotion of tumorigenicity and metastasis of breast cancercells in vivo. Mol Cancer Res 2003;1:165–75.

Baselga J. Clinical trials of single-agent trastuzumab (Herceptin). Semin Oncol2000a;27:20–6.

Baselga J. Current and planned clinical trials with trastuzumab (Herceptin).Semin Oncol 2000b;27:27–32.

Ben-BaruchN,YardenY.Neu differentiation factors: a family of alternatively splicedneuronal and mesenchymal factors. Proc Soc Exp Biol Med 1994;206:221–7.

Bentzinger CF, Barzaghi P, Lin S, Ruegg MA. Overexpression of mini-agrin inskeletal muscle increases muscle integrity and regenerative capacity inlaminin-alpha2-deficient mice. FASEB J 2005;19:934–42.

Berger MS, Locher GW, Saurer S, Gullick WJ, Waterfield MD, Groner B, et al.Correlation of c-erbB-2 gene amplification and protein expression in humanbreast carcinomawith nodal status and nuclear grading. Cancer Res 1988;48:1238–43.


Bermingham-McDonogh O, McCabe KL, Reh TA. Effects of GGF/neuregulinson neuronal survival and neurite outgrowth correlate with erbB2/neuexpression in developing rat retina. Development 1996;122:1427–38.

Berzin TM, Zipser BD, Rafii MS, Kuo-Leblanc V, Yancopoulos GD, Glass DJ,et al. Agrin and microvascular damage in Alzheimer's disease. NeurobiolAging 2000;21:349–55.

Bezakova G, Ruegg MA. New insights into the roles of agrin. Nat Rev Mol CellBiol 2003;4:295–308.

Biroc SL, Payan DG, Fisher JM. Isoforms of agrin are widely expressed in thedeveloping rat and may function as protease inhibitors. J Biol Chem1993;268:25108–17.

Bixby JL, Baerwald-De la Torre K, Wang C, Rathjen FG, Ruegg MA. Aneuronal inhibitory domain in the N-terminal half of agrin. J Neurobiol2002;50:164–79.

Black IB. Trophic regulation of synaptic plasticity. J Neurobiol 1999;41:108–18.Blouin JL, Dombroski BA, Nath SK, Lasseter VK, Wolyniec PS, Nestadt G,

et al. Schizophrenia susceptibility loci on chromosomes 13q32 and 8p21.Nat Genet 1998;20:70–3.

Bose CM, Qiu D, Bergamaschi A, Gravante B, Bossi M, Villa A, et al. Agrincontrols synaptic differentiation in hippocampal neurons. J Neurosci2000;20:9086–95.

Bowe MA, Deyst KA, Leszyk JD, Fallon JR. Identification and purification of anagrin receptor from Torpedo postsynaptic membranes: a heteromeric complexrelated to the dystroglycans. Neuron 1994;12:1173–80.

Brines ML, Dare AO, de Lanerolle NC. The cardiac glycoside ouabainpotentiates excitotoxic injury of adult neurons in rat hippocampus. NeurosciLett 1995;191:145–8.

Britsch S. The neuregulin-I/ErbB signaling system in development and disease.Adv Anat Embryol Cell Biol 2007;190:1–65.

Brown N, Deb K, Paria BC, Das SK, Reese J. Embryo-uterine interactions viathe neuregulin family of growth factors during implantation in the mouse.Biol Reprod 2004;71:2003–11.

Buonanno A, Fischbach GD. Neuregulin and ErbB receptor signaling pathwaysin the nervous system. Curr Opin Neurobiol 2001;11:287–96.

Burden SJ. Synapse-specific gene expression. Trends Genet 1993;9:12–6.Burden S, Yarden Y. Neuregulins and their receptors: a versatile signaling

module in organogenesis and oncogenesis. Neuron 1997;18:847–55.Burgess DL, Biddlecome GH, McDonough SI, Diaz ME, Zilinski CA, Bean BP,

et al. beta subunit reshuffling modifies N- and P/Q-type Ca2+ channelsubunit compositions in lethargic mouse brain. Mol Cell Neurosci1999;13:293–311.

Burgess RW, Skarnes WC, Sanes JR. Agrin isoforms with distinct aminotermini: differential expression, localization, and function. J Cell Biol2000;151:41–52.

Calaora V, Rogister B, Bismuth K, Murray K, Brandt H, Leprince P, et al.Neuregulin signaling regulates neural precursor growth and the generation ofoligodendrocytes in vitro. J Neurosci 2001;21:4740–51.

Campagna JA, Ruegg MA, Bixby JL. Agrin is a differentiation-inducing “stopsignal” for motoneurons in vitro. Clin Exp Pharmacol Physiol 1995;22:961–5.

Campanelli JT, Roberds SL, Campbell KP, Scheller RH. A role for dystrophin-associated glycoproteins and utrophin in agrin-induced AChR clustering.Cell 1994;77:663–74.

Campbell KP, Kahl SD. Association of dystrophin and an integral membraneglycoprotein. Nature 1989;338:259–62.

Cannella B, Hoban CJ, Gao YL, Garcia-Arenas R, Lawson D, Marchionni M,et al. The neuregulin, glial growth factor 2, diminishes autoimmunedemyelination and enhances remyelination in a chronic relapsing modelfor multiple sclerosis. Proc Natl Acad Sci U S A 1998;95:10100–5.

Cannella B, Pitt D, Marchionni M, Raine CS. Neuregulin and erbB receptorexpression in normal and diseased human white matter. J Neuroimmunol1999;100:233–42.

Canoll PD, Musacchio JM, Hardy R, Reynolds R, Marchionni MA, Salzer JL.GGF/neuregulin is a neuronal signal that promotes the proliferation andsurvival and inhibits the differentiation of oligodendrocyte progenitors.Neuron 1996;17:229–43.

Carraway III KL, Weber JL, Unger MJ, Ledesma J, Yu N, Gassmann M, et al.Neuregulin-2, a new ligand of ErbB3/ErbB4-receptor tyrosine kinases.Nature 1997;387:512–6.

Chaudhury AR, Gerecke KM, Wyss JM, Morgan DG, Gordon MN, Carroll SL.Neuregulin-1 and erbB4 immunoreactivity is associated with neuriticplaques in Alzheimer disease brain and in a transgenic model of Alzheimerdisease. J Neuropathol Exp Neurol 2003;62:42–54.

Chen MS, Bermingham-McDonogh O, Danehy Jr FT, Nolan C, Scherer SS,Lucas J, et al. Expression of multiple neuregulin transcripts in postnatal ratbrains. J Comp Neurol 1994;349:389–400.

Chen S, Velardez MO, Warot X, Yu ZX, Miller SJ, Cros D, et al. Neuregulin 1-erbB signaling is necessary for normal myelination and sensory function. JNeurosci 2006;26:3079–86.

Cote P, Lindenbaum MH, Carbonetto S. Dystroglycan is essential for earlyembryonic development. Mol Biol Cell 1997;8:1283.

Cote PD, Moukhles H, Lindenbaum M, Carbonetto S. Chimaeric mice deficientin dystroglycans develop muscular dystrophy and have disrupted myoneuralsynapses. Nat Genet 1999;23:338–42.

Cotman SL, Halfter W, Cole GJ. Agrin binds to beta-amyloid (Abeta), acceleratesabeta fibril formation, and is localized toAbeta deposits in Alzheimer's diseasebrain. Mol Cell Neurosci 2000;15:183–98.

Crone SA, Zhao YY, Fan L, Gu Y, Minamisawa S, Liu Y, et al. ErbB2 isessential in the prevention of dilated cardiomyopathy. Nat Med 2002;8:459–65.

CuriglianoG, Spitaleri G, Pietri E,RescignoM, deBraud F, CardilloA, et al. Breastcancer vaccines: a clinical reality or fairy tale? Ann Oncol 2006;17:750–62.

Dammann CE, Nielsen HC, Carraway III KL. Role of neuregulin-1 beta in thedeveloping lung. Am J Respir Crit Care Med 2003;167:1711–6.

Davies AM, Wright EM. Neurotrophic factors. Neurotrophin autocrine loops.Curr Biol 1995;5:723–6.

de Carvalho Aguiar P, Sweadner KJ, Penniston JT, Zaremba J, Liu L, Caton M,et al. Mutations in the Na+/K+-ATPase alpha3 gene ATP1A3 are associatedwith rapid-onset dystonia parkinsonism. Neuron 2004;43:169–75.

DeChiara TM, Bowen DC, Valenzuela DM, Simmons MV, Poueymirou WT,Thomas S, et al. The receptor tyrosine kinase MuSK is required forneuromuscular junction formation in vivo. Cell 1996;85:501–12.

Deconinck N, Dan B. Pathophysiology of duchenne muscular dystrophy:current hypotheses. Pediatr Neurol 2007;36:1–7.

Dennis CL, Tinsley JM, Deconinck AE, Davies KE. Molecular and functionalanalysis of the utrophin promoter. Nucleic Acids Res 1996;24:1646–52.

Denzer AJ, Gesemann M, Schumacher B, Ruegg MA. An amino-terminalextension is required for the secretion of chick agrin and its binding toextracellular matrix. Neuron 1995;15:1365–74.

Denzer AJ, Hauser DM, Gesemann M, Ruegg MA. Synaptic differentiation: therole of agrin in the formation and maintenance of the neuromuscular junction.Histochem Cell Biol 1997;108:249–55.

Dimitropoulou A, Bixby JL. Motor neurite outgrowth is selectively inhibited bycell surface MuSK and agrin. Mol Cell Neurosci 2005;28:292–302.

Disis ML, Shiota FM, Cheever MA. Human HER-2/neu protein immunizationcircumvents tolerance to rat neu: a vaccine strategy for 'self' tumourantigens. Immunology 1998;93:192–9.

Disis ML, Grabstein KH, Sleath PR, Cheever MA. Generation of immunity tothe HER-2/neu oncogenic protein in patients with breast and ovarian cancerusing a peptide-based vaccine. Clin Cancer Res 1999;5:1289–97.

Dong Z, Brennan A, Liu N, Yarden Y, Lefkowitz G, Mirsky R, et al. Neudifferentiation factor is a neuron-glia signal and regulates survival, prolifera-tion, and maturation of rat Schwann cell precursors. Neuron 1995;15:585–96.

Durbeej M, Campbell KP. Muscular dystrophies involving the dystrophin–glycoprotein complex: an overview of current mouse models. Curr OpinGenet Dev 2002;12:349–61.

Dustin ML. Membrane domains and the immunological synapse: keeping Tcells resting and ready. J Clin Invest 2002;109:155–60.

Ehmsen J, Poon E, Davies K. The dystrophin-associated protein complex. J CellSci 2002;115:2801–3.

Erickson SL, O'Shea KS, Ghaboosi N, Loverro L, Frantz G, Bauer M, et al.ErbB3 is required for normal cerebellar and cardiac development: acomparison with ErbB2-and heregulin-deficient mice. Development1997;124:4999–5011.

Ervasti JM, Campbell KP. A role for the dystrophin-glycoprotein complex as atransmembrane linker between laminin and actin. J Cell Biol 1993;122:809–23.


Ervasti JM, Ohlendieck K, Kahl SD, Gaver MG, Campbell KP. Deficiency of aglycoprotein component of the dystrophin complex in dystrophic muscle.Nature 1990;345:315–9.

Escher P, Lacazette E, Courtet M, Blindenbacher A, Landmann L, Bezakova G,et al. Synapses form in skeletal muscles lacking neuregulin receptors.Science 2005;308:1920–3.

Falls DL. Neuregulins: functions, forms, and signaling strategies. Exp Cell Res2003;284:14–30.

Ferns M, Hoch W, Campanelli JT, Rupp F, Hall ZW, Scheller RH. RNA splicingregulates agrin-mediated acetylcholine receptor clustering activity on culturedmyotubes. Neuron 1992;8:1079–86.

Ferns MJ, Campanelli JT, Hoch W, Scheller RH, Hall Z. The ability of agrin tocluster AChRs depends on alternative splicing and on cell surfaceproteoglycans. Neuron 1993;11:491–502.

Ferreira A. Abnormal synapse formation in agrin-depleted hippocampalneurons. J Cell Sci 1999;112(Pt 24):4729–38.

Ferrer I, Planas AM. Signaling of cell death and cell survival following focalcerebral ischemia: life and death struggle in the penumbra. J NeuropatholExp Neurol 2003;62:329–39.

Fischbach GD, Rosen KM. ARIA: a neuromuscular junction neuregulin. AnnuRev Neurosci 1997;20:429–58.

Flores AI, Mallon BS, Matsui T, Ogawa W, Rosenzweig A, Okamoto T, et al.Akt-mediated survival of oligodendrocytes induced by neuregulins. JNeurosci 2000;20:7622–30.

Fuerst PG, Rauch SM, Burgess RW. Defects in eye development in transgenicmice overexpressing the heparan sulfate proteoglycan agrin. Dev Biol2007;303:165–80.

Gadek JE, Pacht ER. The protease–antiprotease balance within the human lung:implications for the pathogenesis of emphysema. Lung 1990;168:552–64[Suppl].

Garcia-Osta A, Tsokas P, Pollonini G, Landau EM, Blitzer R, Alberini CM.MuSK expressed in the brain mediates cholinergic responses, synapticplasticity, and memory formation. J Neurosci 2006;26:7919–32.

Garratt AN, Voiculescu O, Topilko P, Charnay P, Birchmeier C. A dual role oferbB2 in myelination and in expansion of the Schwann cell precursor pool. JCell Biol 2000;148:1035–46.

Gascoigne NR, Zal T. Molecular interactions at the Tcell-antigen-presenting cellinterface. Curr Opin Immunol 2004;16:114–9.

Gassmann M, Casagranda F, Orioli D, Simon H, Lai C, Klein R, et al. Aberrantneural and cardiac development in mice lacking the ErbB4 neuregulinreceptor. Nature 1995;378:390–4.

Gautam M, Noakes PG, Moscoso L, Rupp F, Scheller RH, Merlie JP, et al.Defective neuromuscular synaptogenesis in agrin-deficient mutant mice.Cell 1996;85:525–35.

Gee SH, Montanaro F, Lindenbaum MH, Carbonetto S. Dystroglycan-alpha, adystrophin-associated glycoprotein, is a functional agrin receptor. Cell1994;77:675–86.

Gesemann M, Denzer AJ, Ruegg MA. Acetylcholine receptor-aggregatingactivity of agrin isoforms and mapping of the active site. Dev Biol1995;167:458–68.

Gesemann M, Brancaccio A, Schumacher B, Ruegg MA. Agrin is a high-affinity binding protein of dystroglycan in non-muscle tissue. J Biol Chem1998;273:600–5.

Gingras J, Ferns M. Expression and localization of agrin during sympatheticsynapse formation in vitro. J Neurobiol 2001;48:228–42.

Gingras J, Rassadi S, Cooper E, Ferns M. Agrin plays an organizing role in theformation of sympathetic synapses. J Cell Biol 2002;158:1109–18.

GlassDJ, BowenDC, Stitt TN, RadziejewskiC, Bruno J, RyanTE, et al. Agrin actsvia a MuSK receptor complex. Cell 1996a;85:513–23.

Glass DJ, DeChiara TM, Stitt TN, DiStefano PS, Valenzuela DM, YancopoulosGD. The receptor tyrosine kinaseMuSK is required for neuromuscular junctionformation and is a functional receptor for agrin. FEBS Lett 1996b;379:63–8.

Goodearl AD, Davis JB, Mistry K, Minghetti L, Otsu M, Waterfield MD, et al.Purification of multiple forms of glial growth factor. J Biol Chem 1993;268:18095–102.

Groffen AJ, RueggMA,DijkmanH, van deVelden TJ, Buskens CA, van denBornJ, et al. Agrin is a major heparan sulfate proteoglycan in the human glomerularbasement membrane. J Neurobiol 1997;33:999–1018.

Groffen AJ, Buskens CA, van Kuppevelt TH, Veerkamp JH, Monnens LA, vanden Heuvel LP. Primary structure and high expression of human agrin inbasement membranes of adult lung and kidney. Eur J Biochem1998;254:123–8.

Groffen AJ, Veerkamp JH, Monnens LA, van den Heuvel LP. Recent insights intothe structure and functions of heparan sulfate proteoglycans in the humanglomerular basement membrane [In Process Citation]. Nephrol Dial Transplant1999;14:2119–29.

Gu Z, Jiang Q, Fu AK, Ip NY, Yan Z. Regulation of NMDA receptors by neuregulinsignaling in prefrontal cortex. J Neurosci 2005;25:4974–84.

Guo WP, Wang J, Li RX, Peng YW. Neuroprotective effects of neuregulin-1 inrat models of focal cerebral ischemia. Brain Res 2006;1087:180–5.

Haenggi T, Fritschy JM. Role of dystrophin and utrophin for assembly andfunction of the dystrophin glycoprotein complex in non-muscle tissue. CellMol Life Sci 2006;63:1614–31.

Haenggi T, Schaub MC, Fritschy JM. Molecular heterogeneity of thedystrophin-associated protein complex in the mouse kidney nephron:differential alterations in the absence of utrophin and dystrophin. Cell TissueRes 2005;319:299–313.

Halfter W, Schurer B, Yip J, Yip L, Tsen G, Lee JA, et al. Distribution andsubstrate properties of agrin, a heparan sulfate proteoglycan of developingaxonal pathways. Neuroscience 1997;79:191–201.

Harari D, Tzahar E, Romano J, Shelly M, Pierce JH, Andrews GC, et al.Neuregulin-4: a novel growth factor that acts through the ErbB-4 receptortyrosine kinase. Oncogene 1999;18:2681–9.

Harisi R, Dudas J, Timar F, Pogany G, Paku S, Timar J, et al. Antiproliferative andantimigratory effects of doxorubicin in human osteosarcoma cells exposed toextracellular matrix. Anticancer Res 2005;25:805–13.

Hausser HJ, Ruegg MA, Brenner RE, Ksiazek I. Agrin is highly expressed bychondrocytes and is required for normal growth. Histochem Cell Biol2007;127:363–74.

Henry MD, Campbell KP. A role for dystroglycan in basement membraneassembly. Cell 1998;95:859–70.

Hilgenberg LG, Smith MA. Agrin signaling in cortical neurons is mediated by atyrosine kinase-dependent increase in intracellular Ca2+ that engages bothCaMKII and MAPK signal pathways. J Neurobiol 2004;61:289–300.

Hilgenberg LG, Ho KD, Lee D, O'Dowd DK, Smith MA. Agrin regulatesneuronal responses to excitatory neurotransmitters in vitro and in vivo. MolCell Neurosci 2002;19:97–110.

Hilgenberg LG, Su H, Gu H, O'Dowd DK, Smith MA. Alpha3Na+/K+-ATPaseis a neuronal receptor for agrin. Cell 2006;125:359–69.

Hippenmeyer S, Shneider NA, Birchmeier C, Burden SJ, Jessell TM, Arber S. Arole for neuregulin1 signaling in muscle spindle differentiation. Neuron2002;36:1035–49.

Ho WH, Armanini MP, Nuijens A, Phillips HS, Osheroff PL. Sensory and motorneuron-derived factor. A novel heregulin variant highly expressed in sensory andmotor neurons. J Biol Chem 1995;270:14523–32.

Hoch W, Ferns M, Campanelli JT, Hall ZW, Scheller RH. Developmentalregulation of highly active alternatively spliced forms of agrin. Neuron1993;11:479–90.

Hoch W, Campanelli JT, Harrison S, Scheller RH. Structural domains of agrinrequired for clustering of nicotinic acetylcholine receptors. J Cell Biol1994;126:1–4.

Holmes WE, Sliwkowski MX, Akita RW, Henzel WJ, Lee J, Park JW, et al.Identification of heregulin, a specific activator of p185erbB2. Science1992;256:1205–10.

Ibraghimov-Beskrovnaya O, Ervasti JM, Leveille CJ, Slaughter CA, SernettSW, Campbell KP. Primary structure of dystrophin-associated glyco-proteins linking dystrophin to the extracellular matrix. Nature 1992;355:696–702.

Jacobelli J, Andres PG, Boisvert J, Krummel MF. New views of theimmunological synapse: variations in assembly and function. Curr OpinImmunol 2004;16:345–52.

Jacobson C, Montanaro F, Lindenbaum M, Carbonetto S, Ferns M. alpha-Dystroglycan functions in acetylcholine receptor aggregation but is not acoreceptor for agrin-MuSK signaling. J Neurosci 1998;18:6340–8.

Jacobson C, Cote PD, Rossi SG, Rotundo RL, Carbonetto S. The dystroglycancomplex is necessary for stabilization of acetylcholine receptor clusters at


neuromuscular junctions and formation of the synaptic basement membrane.J Cell Biol 2001;152:435–50.

Jacobson C, Duggan D, Fischbach G. Neuregulin induces the expression oftranscription factors and myosin heavy chains typical of muscle spindles incultured human muscle. Proc Natl Acad Sci U S A 2004;101:12218–23.

Jaworski A, Burden SJ. Neuromuscular synapse formation in mice lackingmotor neuron- and skeletal muscle-derived Neuregulin-1. J Neurosci2006;26:655–61.

Jessell TM, Siegel RE, Fischbach GD. Induction of acetylcholine receptors oncultured skeletal muscle by a factor extracted from brain and spinal cord.Proc Natl Acad Sci U S A 1979;76:5397–401.

Jessen KR, Mirsky R. The origin and development of glial cells in peripheralnerves. Nat Rev Neurosci 2005;6:671–82.

Jo SA, Zhu X, Marchionni MA, Burden SJ. Neuregulins are concentrated atnerve-muscle synapses and activate ACh- receptor gene expression. Nature1995;373:158–61.

Khan AA, Bose C, Yam LS, Soloski MJ, Rupp F. Physiological regulation of theimmunological synapse by agrin. Science 2001;292:1681–6.

Kim JH, Huganir RL, Organization and regulation of proteins at synapses[published erratum appears in Curr Opin Cell Biol 1999 Jun;11(3):407–8].Curr Opin Cell Biol 1999;11:248–54.

Kim D, Chi S, Lee KH, Rhee S, Kwon YK, Chung CH, et al. Neuregulinstimulates myogenic differentiation in an autocrine manner. J Biol Chem1999;274:15395–400.

Kim MJ, Liu IH, Song Y, Lee JA, Halfter W, Balice-Gordon RJ, et al. Agrin isrequired for posterior development and motor axon outgrowth andbranching in embryonic zebrafish. Glycobiology 2007;17:231–47.

Kopp DM, Trachtenberg JT, Thompson WJ. Glial growth factor rescuesSchwann cells of mechanoreceptors from denervation-induced apoptosis. JNeurosci 1997;17:6697–706.

Koulen P, Honig LS, Fletcher EL, Kroger S. Expression, distribution andultrastructural localization of the synapse-organizing molecule agrin in themature avian retina. Eur J Neurosci 1999;11:4188–96.

Kramer R, Bucay N, Kane DJ, Martin LE, Tarpley JE, Theill LE. Neuregulinswith an Ig-like domain are essential for mouse myocardial and neuronaldevelopment. Proc Natl Acad Sci U S A 1996;93:4833–8.

Kroger S. Differential distribution of agrin isoforms in the developing and adultavian retina. Mol Cell Neurosci 1997;10:149–61.

Kuang W, Xu H, Vachon PH, Liu L, Loechel F, Wewer UM, et al. Merosin-deficient congenital muscular dystrophy. Partial genetic correction in twomouse models [published erratum appears in J Clin Invest 1998 Sep 15;102(6):following 1275]. J Clin Invest 1998;102:844–52.

Kumar P, Ferns MJ, Meizel S. Identification of agrinSN isoform and muscle-specific receptor tyrosine kinase (MuSK) [corrected] in sperm. BiochemBiophys Res Commun 2006;342:522–8.

Kummer TT, Misgeld T, Sanes JR. Assembly of the postsynaptic membrane at theneuromuscular junction: paradigm lost. Curr Opin Neurobiol 2006;16:74–82.

Law AJ, Shannon Weickert C, Hyde TM, Kleinman JE, Harrison PJ.Neuregulin-1 (NRG-1) mRNA and protein in the adult human brain.Neuroscience 2004;127:125–36.

Lee KF, Simon H, Chen H, Bates B, Hung MC, Hauser C. Requirement forneuregulin receptor erbB2 in neural and cardiac development. Nature1995;378:394–8.

Lemke G. Neuregulins in development. Mol Cell Neurosci 1996;7:247–62.Lewis DA, Moghaddam B. Cognitive dysfunction in schizophrenia: conver-

gence of gamma-aminobutyric acid and glutamate alterations. Arch Neurol2006;63:1372–6.

Li L, Cleary S, Mandarano MA, Long W, Birchmeier C, Jones FE. The breastproto-oncogene, HRGalpha regulates epithelial proliferation and lobuloalveo-lar development in the mouse mammary gland. Oncogene 2002;21:4900–7.

Li B, Woo RS, Mei L, Malinow R. The neuregulin-1 receptor erbB4 controlsglutamatergic synapse maturation and plasticity. Neuron 2007;54:583–97.

Liu Y, Ford B, Mann MA, Fischbach GD. Neuregulins increase alpha7 nicotinicacetylcholine receptors and enhance excitatory synaptic transmission inGABAergic interneurons of the hippocampus. J Neurosci 2001;21:5660–9.

Liu J, Nethery D, Kern JA. Neuregulin-1 induces branching morphogenesis inthe developing lung through a P13K signal pathway. Exp Lung Res2004;30:465–78.

Liu CM, Hwu HG, Fann CS, Lin CY, Liu YL, Ou-Yang WC, et al. Linkageevidence of schizophrenia to loci near neuregulin 1 gene on chromosome8p21 in Taiwanese families. Am J Med Genet B Neuropsychiatr Genet2005;134:79–83.

Liu X, Gu X, Li Z, Li X, Li H, Chang J, et al. Neuregulin-1/erbB-activationimproves cardiac function and survival in models of ischemic, dilated, andviral cardiomyopathy. J Am Coll Cardiol 2006;48:1438–47.

Lovering RM, Porter NC, Bloch RJ. The muscular dystrophies: from genes totherapies. Phys Ther 2005;85:1372–88.

Ma YJ, Hill DF, Creswick KE, Costa ME, Cornea A, Lioubin MN, et al.Neuregulins signaling via a glial erbB-2-erbB-4 receptor complex contribute tothe neuroendocrine control of mammalian sexual development. J Neurosci1999;19:9913–27.

Mahanthappa NK, Anton ES, Matthew WD. Glial growth factor 2, a solubleneuregulin, directly increases Schwann cell motility and indirectly promotesneurite outgrowth. J Neurosci 1996;16:4673–83.

Marchionni MA, Goodearl AD, Chen MS, Bermingham-McDonogh O, Kirk C,Hendricks M, et al. Glial growth factors are alternatively spliced erbB2ligands expressed in the nervous system. Nature 1993;362:312–8.

McCroskery S, Chaudhry A, Lin L, Daniels MP. Transmembrane agrin regulatesfilopodia in rat hippocampal neurons in culture. Mol Cell Neurosci2006;33:15–28.

McMahan UJ. The agrin hypothesis. J Physiol (Paris) 1990;84:78–81.Meier T, Hauser DM, Chiquet M, Landmann L, RueggMA, Brenner HR. Neural

agrin induces ectopic postsynaptic specializations in innervated musclefibers. J Neurosci 1997;17:6534–44.

Merlie JP, Sanes JR. Concentration of acetylcholine receptor mRNA in synapticregions of adult muscle fibres. Nature 1985;317:66–8.

Meyer D, Birchmeier C. Multiple essential functions of neuregulin indevelopment. Nature 1995;378:386–90.

Michailov GV, Sereda MW, Brinkmann BG, Fischer TM, Haug B, BirchmeierC, et al. Axonal neuregulin-1 regulates myelin sheath thickness. Science2004;304:700–3.

Miyagoe Y, Hanaoka K, Nonaka I, Hayasaka M, Nabeshima Y, Arahata K, et al.Laminin alpha2 chain-null mutant mice by targeted disruption of the Lama2gene: a new model of merosin (laminin 2)-deficient congenital musculardystrophy. FEBS Lett 1997;415:33–9.

Moll J, Barzaghi P, Lin S, Bezakova G, Lochmuller H, Engvall E, et al. An agrinminigene rescues dystrophic symptoms in a mouse model for congenitalmuscular dystrophy. Nature 2001;413:302–7.

Muss HB, Thor AD, Berry DA, Kute T, Liu ET, Koerner F, et al. c-erbB-2expression and response to adjuvant therapy inwomenwith node-positive earlybreast cancer. N Engl J Med 1994;330:1260–6.

Nitkin RM, Smith MA, Magill C, Fallon JR, Yao YM, Wallace BG, et al.Identification of agrin, a synaptic organizing protein form Torpedo electricorgan. J Cell Biol 1987;105:2471–8.

Noguchi H, Sakamoto C, Wada K, Akamatsu T, Uchida T, Tatsuguchi A, et al.Expression of heregulin alpha, erbB2, and erbB3 and their influences onproliferation of gastric epithelial cells. Gastroenterology 1999;117:1119–27.

O'Connor LT, Lauterborn JC, Gall CM, Smith MA. Localization and alternativesplicing of agrin mRNA in adult rat brain: transcripts encoding isoforms thataggregate acetylcholine receptors are not restricted to cholinergic regions.Neurochem Int 1994;24:301–16.

Ozaki M, Sasner M, Yano R, Lu HS, Buonanno A. Neuregulin-beta inducesexpression of an NMDA-receptor subunit. Nature 1997;390:691–4.

Ozaki M, Tohyama K, Kishida H, Buonanno A, Yano R, Hashikawa T. Roles ofneuregulin in synaptogenesis between mossy fibers and cerebellar granulecells. J Neurosci Res 2000;59:612–23.

Park SK, Solomon D, Vartanian T. Growth factor control of CNS myelination.Dev Neurosci 2001;23:327–37.

Parker MW, Chen Y, Hallenbeck JM, Ford BD. Neuregulin expression afterfocal stroke in the rat. Neurosci Lett 2002;334:169–72.

Patel NV, Acarregui MJ, Snyder JM, Klein JM, Sliwkowski MX, Kern JA.Neuregulin-1 and human epidermal growth factor receptors 2 and 3 play arole in human lung development in vitro. Am J Respir Cell Mol Biol2000;22:432–40.

Peck JA, Stopa EG. Agrin and microvascular damage in Alzheimer's disease.Med Health R I 2002;85:202–6.


Peles E, Yarden Y. Neu and its ligands: from an oncogene to neural factors.BioEssays 1993;15:815–24.

Peles E, Bacus SS, Koski RA, Lu HS, Wen D, Ogden SG, et al. Isolation of theneu/HER-2 stimulatory ligand: a 44 kd glycoprotein that inducesdifferentiation of mammary tumor cells. Cell 1992;69:205–16.

Prevot V, Rio C, Cho GJ, Lomniczi A, Heger S, Neville CM, et al. Normal femalesexual development requires neuregulin-erbB receptor signaling in hypotha-lamic astrocytes. J Neurosci 2003;23:230–9.

Raats CJ, Bakker MA, Hoch W, Tamboer WP, Groffen AJ, van den Heuvel LP,et al. Differential expression of agrin in renal basement membranes asrevealed by domain-specific antibodies. J Biol Chem 1998;273:17832–8.

Raats CJ, Luca ME, Bakker MA, Van Der Wal A, Heeringa P, Van Goor H, et al.Reduction in glomerular heparan sulfate correlates with complementdeposition and albuminuria in active Heymann nephritis [In Process Citation].J Am Soc Nephrol 1999;10:1689–99.

Raats CJ, van den Born J, Bakker MA, Oppers-Walgreen B, Pisa BJ, DijkmanHB, et al. Expression of agrin, dystroglycan, and utrophin in normal renaltissue and in experimental glomerulopathies. Am J Pathol 2000;156:1749–65.

Raff MC, Abney E, Brockes JP, Hornby-Smith A. Schwann cell growth factors.Cell 1978;15:813–22.

RascherG, FischmannA,Kroger S,Duffner F, Grote EH,WolburgH. Extracellularmatrix and the blood-brain barrier in glioblastoma multiforme: spatialsegregation of tenascin and agrin. Acta Neuropathol (Berl) 2002;104:85–91.

Rentschler S, Zander J, Meyers K, France D, Levine R, Porter G, et al.Neuregulin-1 promotes formation of the murine cardiac conduction system.Proc Natl Acad Sci U S A 2002;99:10464–9.

Rieff HI, Raetzman LT, Sapp DW, Yeh HH, Siegel RE, Corfas G. Neuregulininduces GABA(A) receptor subunit expression and neurite outgrowth incerebellar granule cells. J Neurosci 1999;19:10757–66.

Rio C, Rieff HI, Qi P, Khurana TS, Corfas G. Neuregulin and erbB receptors play acritical role in neuronal migration. Neuron 1997;19:39–50.

Rohrbach S, Yan X, Weinberg EO, Hasan F, Bartunek J, Marchionni MA, et al.Neuregulin in cardiac hypertrophy in rats with aortic stenosis. Differentialexpression of erbB2 and erbB4 receptors. Circulation 1999;100:407–12.

Ross JS, Fletcher JA. The HER-2/neu oncogene in breast cancer: prognosticfactor, predictive factor, and target for therapy. Oncologist 1998;3:237–52.

RueggMA, TsimKW,HortonSE,Kroger S, EscherG,GenschEM, et al. The agringene codes for a family of basal lamina proteins that differ in function anddistribution. Neuron 1992;8:865–8.

Rupp F, Payan DG, Magill-Solc C, Cowan DM, Scheller RH. Structure andexpression of a rat agrin. Neuron 1991;6:869–78.

Rusnak DW, Affleck K, Cockerill SG, Stubberfield C, Harris R, Page M, et al.The characterization of novel, dual ErbB-2/EGFR, tyrosine kinaseinhibitors: potential therapy for cancer. Cancer Res 2001;61:7196–203.

Sanderson RD, Yang Y, Kelly T, MacLeod V, Dai Y, Theus A. Enzymaticremodeling of heparan sulfate proteoglycans within the tumor microenvir-onment: growth regulation and the prospect of new cancer therapies. J CellBiochem 2005;96:897–905.

Sasisekharan R, Shriver Z, Venkataraman G, Narayanasami U. Roles ofheparan-sulphate glycosaminoglycans in cancer. Nat Rev Cancer 2002;2:521–8.

SerpinskayaAS, FengG, Sanes JR, CraigAM.Synapse formation by hippocampalneurons from agrin-deficient mice. Dev Biol 1999;205:65–78.

Shah NM, Marchionni MA, Isaacs I, Stroobant P, Anderson DJ. Glial growthfactor restricts mammalian neural crest stem cells to a glial fate. Cell1994;77:349–60.

Silberberg G, Darvasi A, Pinkas-Kramarski R, Navon R. The involvement ofErbB4 with schizophrenia: association and expression studies. Am J MedGenet B Neuropsychiatr Genet 2006;141:142–8.

Slamon D, Pegram M. Rationale for trastuzumab (Herceptin) in adjuvant breastcancer trials. Semin Oncol 2001;28:13–9.

Slamon DJ, Clark GM, Wong SG, Levin WJ, Ullrich A, McGuire WL. Humanbreast cancer: correlation of relapse and survival with amplification of theHER-2/neu oncogene. Science 1987;235:177–82.

Sliwkowski MX, Lofgren JA, Lewis GD, Hotaling TE, Fendly BM, Fox JA.Nonclinical studies addressing the mechanism of action of trastuzumab(Herceptin). Semin Oncol 1999;26:60–70.

Smith MA, Hilgenberg LG. Agrin in the CNS: a protein in search of a function?NeuroReport 2002;13:1485–95.

Sparano JA. Cardiac toxicity of trastuzumab (Herceptin): implications for thedesign of adjuvant trials. Semin Oncol 2001;28:20–7.

Spence HJ, Dhillon AS, James M, Winder SJ. Dystroglycan, a scaffold for theERK-MAP kinase cascade. EMBO Rep 2004;5:484–9.

Staub O, Rotin D. Regulation of ion transport by protein–protein interactiondomains. Curr Opin Nephrol Hypertens 1997;6:447–54.

Stefansson H, Sigurdsson E, Steinthorsdottir V, Bjornsdottir S, Sigmundsson T,Ghosh S, et al. Neuregulin 1 and susceptibility to schizophrenia. Am J HumGenet 2002;71:877–92.

Stefansson H, Sarginson J, Kong A, Yates P, Steinthorsdottir V, Gudfinnsson E,et al. Association of neuregulin 1 with schizophrenia confirmed in a Scottishpopulation. Am J Hum Genet 2003;72:83–7.

Stefansson H, Steinthorsdottir V, Thorgeirsson TE, Gulcher JR, Stefansson K.Neuregulin 1 and schizophrenia. Ann Med 2004;36:62–71.

Suarez E, Bach D, Cadefau J, Palacin M, Zorzano A, Guma A. A novel role ofneuregulin in skeletal muscle. Neuregulin stimulates glucose uptake,glucose transporter translocation, and transporter expression in musclecells. J Biol Chem 2001;276:18257–64.

Sugita S, Saito F, Tang J, Satz J, Campbell K, Sudhof TC. A stoichiometriccomplex of neurexins and dystroglycan in brain. J Cell Biol 2001;154:435–45.

TanseyMG,ChuGC,Merlie JP. ARIA/HRG regulates AChR epsilon subunit geneexpression at the neuromuscular synapse via activation of phosphatidylinositol3-kinase and Ras/MAPK pathway. J Cell Biol 1996;134:465–76.

Tatrai P, Dudas J, Batmunkh E, Mathe M, Zalatnai A, Schaff Z, et al. Agrin, anovel basement membrane component in human and rat liver, accumulatesin cirrhosis and hepatocellular carcinoma. Lab Invest 2006;86:1149–60.

Tinsley JM, Potter AC, Phelps SR, Fisher R, Trickett JI, Davies KE. Amelioration ofthe dystrophic phenotype of mdx mice using a truncated utrophin transgene [seecomments]. Nature 1996;384:349–53.

Tokita Y, KeinoH,Matsui F, Aono S, IshiguroH, Higashiyama S, et al. Regulationof neuregulin expression in the injured rat brain and cultured astrocytes.J Neurosci 2001;21:1257–64.

Tournell CE, Bergstrom RA, Ferreira A. Progesterone-induced agrin expression inastrocytes modulates glia–neuron interactions leading to synapse formation.Neuroscience 2006;141:1327–38.

Tourtellotte WG, Milbrandt J. Sensory ataxia and muscle spindle agenesis inmice lacking the transcription factor Egr3. Nat Genet 1998;20:87–91.

Toyoda-Ohno H, Obinata M, Matsui Y. Members of the ErbB receptor tyrosinekinases are involved in germ cell development in fetal mouse gonads. DevBiol 1999;215:399–406.

Trachtenberg JT, Thompson WJ. Schwann cell apoptosis at developing neuromus-cular junctions is regulated by glial growth factor. Nature 1996;379:174–7.

Tsen G, Halfter W, Kroger S, Cole GJ. Agrin is a heparan sulfate proteoglycan. JCell Biol 1995a;128:1121–9.

Tsen G, Napier A, Halfter W, Cole GJ. Identification of a novel alternativelyspliced agrin mRNA that is preferentially expressed in non-neuronal cells.Science 1995b;269:362–3.

Tsim KW, Ruegg MA, Escher G, Kroger S, McMahan UJ. cDNA that encodesactive agrin [published erratum appears in Neuron 1992 Aug;9(2):following381]. Neuron 1992;8:691–9.

Uray IP, Connelly JH, Thomazy V, Shipley GL, VaughnWK, Frazier OH, et al. Leftventricular unloading alters receptor tyrosine kinase expression in the failinghuman heart. J Heart Lung Transplant 2002;21:771–82.

Usdin TB, Fischbach GD. Purification and characterization of a polypeptidefrom chick brain that promotes the accumulation of acetylcholine receptorsin chick myotubes. J Cell Biol 1986;103:493–507.

Valenzuela DM, Stitt TN, DiStefano PS, Rojas E, Mattsson K, Compton DL, etal. Receptor tyrosine kinase specific for the skeletal muscle lineage:expression in embryonic muscle, at the neuromuscular junction, and afterinjury. Neuron 1995;15:573–84.

van de Lest CH, Versteeg EM, Veerkamp JH, van Kuppevelt TH. Digestion ofproteoglycans in porcine pancreatic elastase-induced emphysema in rats.Eur Respir J 1995;8:238–45.

van den Hoven MJ, Rops AL, Bakker MA, Aten J, Rutjes N, Roestenberg P, etal. Increased expression of heparanase in overt diabetic nephropathy. KidneyInt 2006;70:2100–8.


van Horssen J, Kleinnijenhuis J, Maass CN, Rensink AA, Otte-Holler I, DavidG, et al. Accumulation of heparan sulfate proteoglycans in cerebellar senileplaques. Neurobiol Aging 2002;23:537–45.

Vartanian T, Corfas G, Li Y, Fischbach GD, Stefansson K. A role for theacetylcholine receptor-inducing protein ARIA in oligodendrocyte develop-ment. Proc Natl Acad Sci U S A 1994;91:11626–30.

Vartanian T, Fischbach G, Miller R. Failure of spinal cord oligodendrocytedevelopment in mice lacking neuregulin. Proc Natl Acad Sci U S A1999;96:731–5.

Verbeek MM, Otte-Holler I, van den Born J, van den Heuvel LP, David G,Wesseling P, et al. Agrin is a major heparan sulfate proteoglycanaccumulating in Alzheimer's disease brain. Am J Pathol 1999;155:2115–25.

Viehover A, Miller RH, Park SK, Fischbach G, Vartanian T. Neuregulin: anoligodendrocyte growth factor absent in active multiple sclerosis lesions.Dev Neurosci 2001;23:377–86.

Warth A, Kroger S, Wolburg H. Redistribution of aquaporin-4 in humanglioblastoma correlates with loss of agrin immunoreactivity from braincapillary basal laminae. Acta Neuropathol (Berl) 2004;107:311–8.

Wolpowitz D, Mason TB, Dietrich P, Mendelsohn M, Talmage DA, Role LW.Cysteine-rich domain isoforms of the neuregulin-1 gene are required formaintenance of peripheral synapses. Neuron 2000;25:79–91.

Woo RS, Li XM, Tao Y, Carpenter-Hyland E, Huang YZ, Weber J, et al.Neuregulin-1 enhances depolarization-induced GABA release. Neuron2007;54:599–610.

Xia W, Mullin RJ, Keith BR, Liu LH, Ma H, Rusnak DW, et al. Anti-tumoractivity of GW572016: a dual tyrosine kinase inhibitor blocks EGFactivation of EGFR/erbB2 and downstream Erk1/2 and AKT pathways.Oncogene 2002;21:6255–63.

Xiao AY, Wang XQ, Yang A, Yu SP. Slight impairment of Na+,K+-ATPasesynergistically aggravates ceramide- and beta-amyloid-induced apoptosis incortical neurons. Brain Res 2002;955:253–9.

Xu Z, Ford BD. Upregulation of erbB receptors in rat brain after middle cerebralarterial occlusion. Neurosci Lett 2005;375:181–6.

Xu Z, Ford GD, Croslan DR, Jiang J, Gates A, Allen R, et al. Neuroprotection byneuregulin-1 following focal stroke is associated with the attenuation ofischemia-induced pro-inflammatory and stress gene expression. Neurobiol Dis2005a;19:461–70.

Xu X, Fu AK, Ip FC, Wu CP, Duan S, Poo MM, et al. Agrin regulates growthcone turning of Xenopus spinal motoneurons. Development 2005b;132:4309–16.

Yang Y, Spitzer E, Meyer D, SachsM, Niemann C, Hartmann G, et al. Sequentialrequirement of hepatocyte growth factor and neuregulin in the morphogen-esis and differentiation of the mammary gland. J Cell Biol 1995;131:215–26.

Yang SH, Armson PF, Cha J, Phillips WD. Clustering of GABAA receptors byrapsyn/43kD protein in vitro. Mol Cell Neurosci 1997;8:430–8.

Yang X, Kuo Y, Devay P, Yu C, Role L. A cysteine-rich isoform of neuregulincontrols the level of expression of neuronal nicotinic receptor channels duringsynaptogenesis. Neuron 1998;20:255–70.

Yang X, Arber S, William C, Li L, Tanabe Y, Jessell TM, et al. Patterning ofmuscle acetylcholine receptor gene expression in the absence of motorinnervation. Neuron 2001;30:399–410.

Yarden Y, Sliwkowski MX. Untangling the ErbB signalling network. Nat RevMol Cell Biol 2001;2:127–37.

Yoshida M, Ozawa E. Glycoprotein complex anchoring dystrophin tosarcolemma. J Biochem (Tokyo) 1990;108:748–52.

Zhang D, SliwkowskiMX,MarkM, Frantz G, Akita R, Sun Y, et al. Neuregulin-3 (NRG3): a novel neural tissue-enriched protein that binds and activatesErbB4. Proc Natl Acad Sci U S A 1997;94:9562–7.

Zhao YY, Sawyer DR, Baliga RR, Opel DJ, Han X, Marchionni MA, et al.Neuregulins promote survival and growth of cardiac myocytes. Persistenceof ErbB2 and ErbB4 expression in neonatal and adult ventricular myocytes.J Biol Chem 1998;273:10261–9.

Agrin and neuregulin, expanding roles and implications for therapeutics

Documents

Transcript of Agrin and neuregulin, expanding roles and implications for therapeutics