Neurulation & Organogenesis. Neurulation Neural cells originate from the neurectoderm Clusters of...
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Transcript of Neurulation & Organogenesis. Neurulation Neural cells originate from the neurectoderm Clusters of...
Neurulation & Organogenesis
Neurulation
• Neural cells originate from the neurectoderm
• Clusters of proneural cells are specified by the proneural genes
• Single neuroblasts are specified within the proneural cluster via lateral inhibition
• Proneural and neurogenic genes, respectively, regulate these specification events
Neurogenesis
Proneural & Neurogenic Genes
• Proneural: Achaete-Scute complex of genes (AS-C)– Achaete (ac), scute (sc), lethal of scute (lsc), asense (as)
• Neurogenic: Notch-Delta pathway– Notch (N), Delta (Dl), Enhancer of split (E(spl)), Hairless
(H), Suppressor of Hairless (Su(H)), brainiac (brn), mastermind (mam), neurlalized (neu), kuzbanian (kuz), big brain (bib)
Acheate Expressionen = purple acheate = black stain
Regulation of Proneural Genes
• hairy (h), gooseberry (gb), Extramacrochaete (emc) – Emc & h are inhibitory bHLH txn factors
– Gb has a homeobox
• ventral nervous system defective (vnd), engrailed (en), wingless (wg), iroquois (iro)
Neurogenic Genes• Juxtacrine signaling
molecules
• Delta (Dl) - ligand
• Notch (N) – receptor
• kuzbanian (kuz) – protease kuz
Su(H)E(spl)
Delta-Notch Signaling
by kuz
Lateral Inhibition Summary• Delta and Notch are expressed in every cell in the proneural
cluster• Dl is usually slightly more highly expressed than N
• Dl activates N• N activates Su(H)• Su(H) displaces H and activates E(spl)• E(spl) inhibits AS-C genes & indirectly, Dl• Without AS-C gene products, neural differentiation is
blocked• AS-C normally activates Dl and other proneural genes
Drosophila Neurogenesis & Vertebrate Neurogenesis Occur Via Homologous Pathways
Mash – mouse acheate-scute homologueDll-1 – delta-like 1
Delta-Notch Signaling in Vertebrates
Drosophila Peripheral Nervous System• proneural clusters form in imaginal discs
• proneural clusters differentiate into SOPs and ultimately into sensory bristles
Differentiation of Sensory Bristles
numb & Notch mutations
SMC (sensory mother cells) also called SOP (sensory organ precursor)
no SMC
OrganogenesisImaginal Disc
Imaginal Discs
Initial Specification of Imaginal Discs
Intersection of wg stripes with Dpp expressing cells specifies discs
Leg Disc Primordia
Wing/HaltereDisc Primordia
Patterning of Wing Discs
Anterior-Posterior specification established by en, & hh with Dpp
at the border
Dorsal-Ventral Polarity in Wing Disc
Apterous protein (green) dorsal wingVestigial protein (red) ventral wing
Wing Disc
Patterning of Wing Discs
dorsal-ventral patterning is established by apterous & vestigial
expression with wg establishing the border
Patterning of Wing DiscsVestigial (green), apterous (red), wingless (purple), cubitus
interuptus (blue)
Patterning of Leg Discs
Eversion of Leg Imaginal Disc
Proximal-distal Axis in Leg Disc
Expression of txn factors in regions of leg disc specifies proximal-distal polarity distalless (dll)(red), dachshund (dac) (green), homothorax (htx) (purple)
Eye Disc Specification
Twin of eyeless(Pax6)
Eyeless (Pax6)
Eyes absent(eya1, 2, 3)
Sine oculus(Six3)
dachshund
Ectopic Expression of ey
Patterning of the Eye Disc
Differentiation in the Eye Disc
AP
Morphogenic Furrow
Progress of Morphogenetic Furrow & Cell Specification in Its Wake
Rhabdomere Specification
Drosophila Compound Eye
Ommatidium 20+ cells;
8 photoreceptors12 accessory cells
800 Ommatidia
Drosophila ommatidium
Go See an Ommatidium @
http://sdb.bio.purdue.edu/fly/virtomm.mov
Analysis of R7 Differentiation through Genetic Mosaics
sev only needed in R7 for R7 differentiationsev functions cell autonomously