Epithelial Mesenchymal Transition

8/3/2019 Epithelial Mesenchymal Transition

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EpithelialEpithelial--MesenchymalMesenchymal

Transition (EMT)Transition (EMT)

Hallmarks of CancerHallmarks of Cancer

19 February 200719 February 2007

Richard M. ShowmanRichard M. Showman


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DEFINITION:DEFINITION:

An orchestrated series of events inAn orchestrated series of events inwhich cellwhich cell--cell and cellcell and cell--extracellularextracellularmatrix (ECM) interactions are alteredmatrix (ECM) interactions are altered

to release epithelial cells from theto release epithelial cells from thesurrounding tissue, the cytoskeletonsurrounding tissue, the cytoskeletonis reorganized to allow movement inis reorganized to allow movement in3 dimensions in the ECM and a new3 dimensions in the ECM and a newtranscriptional program is induced totranscriptional program is induced tomaintain the mesenchymalmaintain the mesenchymalphenotypephenotype


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Cell TypesCell Types

Epithelial cellsEpithelial cells

Mesenchymal cellsMesenchymal cells

All animals start as epithelial cellsAll animals start as epithelial cells

NOTE: Both types can form all three germNOTE: Both types can form all three germlayers, ectoderm, mesoderm andlayers, ectoderm, mesoderm andendoderm (?)endoderm (?)


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Characteristics ofEpithelial CellsCharacteristics ofEpithelial Cells

Typically a sheet 1 cell thickTypically a sheet 1 cell thick

Individual cells abutting each otherIndividual cells abutting each other

Regularly spaced cell junctions andRegularly spaced cell junctions andadhesions between neighboring cellsadhesions between neighboring cells

Tight adhesion between cellsTight adhesion between cells

resulting in inhibition of movementresulting in inhibition of movementaway from the monolayeraway from the monolayer


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Epithelium (cont.)Epithelium (cont.)

Enclose a 3Enclose a 3--dimensional space withindimensional space within

Gives structural definition andGives structural definition and

rigidityrigidityEpithelial sheet is polarizedEpithelial sheet is polarized

Apical and basal surfaces often veryApical and basal surfaces often very

differentdifferentAdheres to different substratesAdheres to different substrates

Has different functionHas different function


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Epithelium (cont)Epithelium (cont)

Movement of epithelial cells is doneMovement of epithelial cells is doneen block with the motive forceen block with the motive force

usually generated within the sheetusually generated within the sheetby the sum of the cells shapeby the sum of the cells shapechanges.changes.

Examples: Gastrulation; NeurulationExamples: Gastrulation; Neurulation


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Characteristics of MesenchymalCharacteristics of Mesenchymal

CellsCellsLack regimented structureLack regimented structure

Few tight intracellular adhesionsFew tight intracellular adhesions

Weak adhesions which allow for easeWeak adhesions which allow for easeof mobilityof mobility

Forms irregular structures that areForms irregular structures that are

not uniform in composition or densitynot uniform in composition or densityMore extended and elongated inMore extended and elongated in

shapeshape


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Mesenchyme (cont.)Mesenchyme (cont.)

Lacks rigid topological specializationLacks rigid topological specialization(no compartments)(no compartments)

Cells move as individuals, not enCells move as individuals, not enblock, often leaving a trailing regionblock, often leaving a trailing regionbehindbehind

Migration mechanistically differentMigration mechanistically differentand more dynamicand more dynamic


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Epithelial and Mesenchymal CellsEpithelial and Mesenchymal Cells


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Discovery ofEMTDiscovery ofEMT

First observed and defined byFirst observed and defined byElizabeth Hay in late 1960s atElizabeth Hay in late 1960s at

HarvardHarvardFirst associated with early stages ofFirst associated with early stages of

embryonic development.embryonic development.

Process is reversible w/unstableProcess is reversible w/unstableintermediateintermediate

EMT Metastable METEMT Metastable MET


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EMT MarkersEMT Markers

Proteins that increase inProteins that increase inabundanceabundance

NN--cadherincadherin VimentinVimentin FibronectinFibronectin

Snail1 (Snail)Snail1 (Snail) Snail2(Slug)Snail2(Slug) TwistTwist GoosecoidGoosecoid FOXC2FOXC2 Sox10Sox10

MMPMMP--22 MMPMMP--33 MMP9MMP9 Integrin v6Integrin v6

Proteins that decrease inProteins that decrease inabundanceabundance

EE--cadherencadheren DesmoplakinDesmoplakin CytokeratinCytokeratin

OccludinOccludin Proteins whose activityProteins whose activity

increasesincreases ILKILK GSKGSK--33 RhoRho Proteins that accumulateProteins that accumulate

in the nucleusin the nucleus --catenincatenin SmadSmad--2/32/3 NFNF-- Snail1 (Snail)Snail1 (Snail) Snail2 (Slug)Snail2 (Slug)

TwistTwist


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TransitionsTransitions


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Events Comprising EMTEvents Comprising EMT

Specification to differentiate into a type ofSpecification to differentiate into a type ofcell that will go through EMTcell that will go through EMT.. SpecificationSpecificationtoward a mesenchymal phenotype initiatestoward a mesenchymal phenotype initiatesmany important changes in genemany important changes in gene

expression and protein function that mustexpression and protein function that mustall work in concert for a developmentalall work in concert for a developmentalEMT to occur correctly. This will direct theEMT to occur correctly. This will direct thesubsequent steps and may requiresubsequent steps and may requirestopping cell division so that thestopping cell division so that thecytoskeleton can be used to drive the cellcytoskeleton can be used to drive the cellshape changes and motility needed forshape changes and motility needed forEMT.EMT.


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EMTEMT

Temporal and spatial patterning of theTemporal and spatial patterning of theprogress of the EMT within the areaprogress of the EMT within the areadestined to undergo EMTdestined to undergo EMT.. Patterning isPatterning is

important in that large areas of epitheliumimportant in that large areas of epitheliumdestined to undergo EMT usually do sodestined to undergo EMT usually do soprogressively from a restricted zone. Thisprogressively from a restricted zone. Thisallows both a necessary maintenance ofallows both a necessary maintenance of

physiological and mechanical continuity ofphysiological and mechanical continuity ofthe remaining epithelium and the spatialthe remaining epithelium and the spatialregulation of morphogenesis.regulation of morphogenesis.


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EMTEMT

Move, or be moved, to the site of EMT,Move, or be moved, to the site of EMT,generally through epithelialgenerally through epithelialmorphogenesismorphogenesis.. Movement of cells to theMovement of cells to thecorrect position is not always acorrect position is not always a

requirement, as they may initially lie thererequirement, as they may initially lie thereto begin with (sea urchins), but in otherto begin with (sea urchins), but in othercases it is clearly required, as in the chickcases it is clearly required, as in the chickor mouse primitive streak or the urodeleor mouse primitive streak or the urodeleamphibian, where large areas ofamphibian, where large areas ofepithelium are moved to a local site ofepithelium are moved to a local site ofingression. The mechanism behind theseingression. The mechanism behind thesemovements is poorly understood in nearlymovements is poorly understood in nearlyall cases.all cases.


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EMTEMT

Alteration or disruption of the basal laminaAlteration or disruption of the basal lamina..Ingressing cells often move past or through aIngressing cells often move past or through abasal lamina, which may mechanically impedebasal lamina, which may mechanically impedetheir ingression and therefore must be disruptedtheir ingression and therefore must be disrupted

prior to ingression, presumably by the ingressingprior to ingression, presumably by the ingressingcells. The mechanism behind this is again poorlycells. The mechanism behind this is again poorlyunderstood. Matrix metaloproteases are thoughtunderstood. Matrix metaloproteases are thoughtto be important in, among other things,to be important in, among other things,remodeling or degrading the extracellular matrixremodeling or degrading the extracellular matrix

during organogenesis, later tissue remodelingduring organogenesis, later tissue remodelingevents, and cancer and perhaps cell migrationevents, and cancer and perhaps cell migrationduring gastrulation but evidence for a role induring gastrulation but evidence for a role inprimary developmental EMTs is lacking so far.primary developmental EMTs is lacking so far.


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EMTEMT

Change in cell shape, generally by an apical actinChange in cell shape, generally by an apical actin--myosinmyosincontractile mechanism and/or changes in adhesioncontractile mechanism and/or changes in adhesion..Ingressing cells often but not always go through a bottleIngressing cells often but not always go through a bottle--shaped stage, which may have two functions: byshaped stage, which may have two functions: byconstricting their apices cells may displace much of theirconstricting their apices cells may displace much of theirintracellular contents basally and initiate movement out ofintracellular contents basally and initiate movement out ofthe epithelium. Perhaps more important, apicalthe epithelium. Perhaps more important, apicalconstrictions reduce the amount of nonconstrictions reduce the amount of non--adhesive apicaladhesive apicalmembrane and circumferential, apical junctions that mustmembrane and circumferential, apical junctions that mustfinally be broken upon ingressing. It also reduces the sizefinally be broken upon ingressing. It also reduces the sizeof the hole left in the epithelium. It is generally thoughtof the hole left in the epithelium. It is generally thoughtthat apical constriction is driven by an actinthat apical constriction is driven by an actin--myosinmyosin--basedbased

contraction, while the apical membrane is reduced bycontraction, while the apical membrane is reduced byendocytosis. Changes in adhesion may also contribute toendocytosis. Changes in adhesion may also contribute tocell shape change on EMT. Cell behaviors in echinodermcell shape change on EMT. Cell behaviors in echinodermgastrulation are consistent with the possibility that cellsgastrulation are consistent with the possibility that cellsround up by loss of basolateral adhesionround up by loss of basolateral adhesion


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EMTEMT

DeDe--epithelializeepithelialize.. We define deWe define de--epithelialization as the lossepithelialization as the lossof the coherent contact between neighbors thatof the coherent contact between neighbors thatcharacterizes a particular epithelium, and the eventual losscharacterizes a particular epithelium, and the eventual lossof an apical membrane domain. This involves a loss of theof an apical membrane domain. This involves a loss of theextensive circumferential apical junctions, specifically theextensive circumferential apical junctions, specifically thecircumapical tight and adherens junctions, in the case ofcircumapical tight and adherens junctions, in the case ofepithelia that are physiologically and mechanically veryepithelia that are physiologically and mechanically veryimpermeant and coherent, but it can also involve loss ofimpermeant and coherent, but it can also involve loss ofthe junctions accounting for the apical coherence of lessthe junctions accounting for the apical coherence of lesscoherent and resistive epitheloid sheets, a state ofcoherent and resistive epitheloid sheets, a state ofepithelialness that is poorly characterized. How theseepithelialness that is poorly characterized. How theseprocesses occur is not understood. The evidence suggestsprocesses occur is not understood. The evidence suggests

that targeted endocytosis of epithelial junctions andthat targeted endocytosis of epithelial junctions andadhesion molecules may be important and the apicaladhesion molecules may be important and the apicalmembrane may eventually be completely eliminated bymembrane may eventually be completely eliminated byendocytosis.endocytosis.


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EMTEMT

IngressIngress.. We define ingression simply as theWe define ingression simply as thewithdrawal of the ingressing cell's apex from thewithdrawal of the ingressing cell's apex from theepithelial layer and into the deep layer. It differsepithelial layer and into the deep layer. It differsfrom defrom de--epithelialization in that a cell could deepithelialization in that a cell could de--epithelialize and not move out of the sheet.epithelialize and not move out of the sheet.Normal ingression is associated with deNormal ingression is associated with de--epithelialization and adoption of basalepithelialization and adoption of basalmesenchymal characteristics, including an activemesenchymal characteristics, including an activemotility and strong traction on deep tissues ormotility and strong traction on deep tissues orstructures, to pull the cell out of the epithelium.structures, to pull the cell out of the epithelium.

The cell might also be squeezed out of theThe cell might also be squeezed out of theremaining epithelium by virtue of the fact thatremaining epithelium by virtue of the fact thatloss of apical coherence is likely to stimulateloss of apical coherence is likely to stimulatewound healingwound healing


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EMTEMT

Differentiate cell behavior and organization characteristic of aDifferentiate cell behavior and organization characteristic of amesenchymal phenotypemesenchymal phenotype.. This process begins prior to deThis process begins prior to de--epithelialization, continues through ingression, and is not yet completeepithelialization, continues through ingression, and is not yet completein recently ingressed cells. Ingressed cells often retain markers of theirin recently ingressed cells. Ingressed cells often retain markers of theirapices shortly after ingression, such as remnants of tight junctions.apices shortly after ingression, such as remnants of tight junctions.Cells must continue the process of turning off epithelial characters andCells must continue the process of turning off epithelial characters andturning on mesenchymal characters. This requires a majorturning on mesenchymal characters. This requires a majorreorganization of the cell, including completely dismantling the apicalreorganization of the cell, including completely dismantling the apical

junctional scaffold that is thought to regulate discrimination betweenjunctional scaffold that is thought to regulate discrimination betweenapical and basalapical and basallateral (e.g. by vesicular traffic, and organization of thelateral (e.g. by vesicular traffic, and organization of thecytoskeleton.) This, with the removal of the apical membrane, results incytoskeleton.) This, with the removal of the apical membrane, results inthe loss of the cell's apicalthe loss of the cell's apicalbasal polarity. The basalbasal polarity. The basallateral membranelateral membranealso must be remodeled, including the removal of epithelial adhesivealso must be remodeled, including the removal of epithelial adhesivemolecules, perhaps by endocytosis, and replacement by mesenchymalmolecules, perhaps by endocytosis, and replacement by mesenchymal--

type adhesion molecules (cadherins, for example) and matrix receptorstype adhesion molecules (cadherins, for example) and matrix receptors(integrins). The cytoskeleton must be remodeled, from what we imagine(integrins). The cytoskeleton must be remodeled, from what we imagineis a static, structural epithelial configuration to a dynamic, migratoryis a static, structural epithelial configuration to a dynamic, migratoryconfiguration, a process that involves change from epithelialconfiguration, a process that involves change from epithelialcytokeratins to mesenchymal vimentins, and probably substantialcytokeratins to mesenchymal vimentins, and probably substantialchanges in regulation of actin polymerization, microtubule dynamics andchanges in regulation of actin polymerization, microtubule dynamics andmyosin function to allow protrusive activity, all poorly understoodmyosin function to allow protrusive activity, all poorly understoodphenomena in embryonic EMTs.phenomena in embryonic EMTs.


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Steps ofEMTSteps ofEMT

First, inductive or otherFirst, inductive or otherspecification events occur,specification events occur,committing the cell to an EMTcommitting the cell to an EMT(dark green), highlighted cell, A).(dark green), highlighted cell, A).Generally but not always, the cellGenerally but not always, the cellundergoes a constriction of itsundergoes a constriction of itsapical region (small thick arrows,apical region (small thick arrows,B,C), a process which probablyB,C), a process which probably

involves either a circumferentialinvolves either a circumferentialcontractile cytoskeleton (B) or acontractile cytoskeleton (B) or acontractile cytoskeletal meshworkcontractile cytoskeletal meshworkspanning the apices (B).spanning the apices (B).Coincident with the apicalCoincident with the apicalconstriction, the cell often beginsconstriction, the cell often beginsto elongate the apicalto elongate the apicalbasal axisbasal axisas cytoplasm is pushed basallyas cytoplasm is pushed basally(small skinny arrows, B,C). The(small skinny arrows, B,C). Thecell also begins to break down thecell also begins to break down thebasal lamina (magenta, Abasal lamina (magenta, AC).C).


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Steps ofEMTSteps ofEMT Other changes may includeOther changes may includeformation of protrusions at theformation of protrusions at the

basal ends (gray, C,D), downbasal ends (gray, C,D), down--regulation of epithelial cellregulation of epithelial celladhesion and celladhesion and cellextracellularextracellularmatrix adhesion receptors, andmatrix adhesion receptors, and

expression of mesenchymalexpression of mesenchymaladhesion moleculesadhesion molecules(basolateral spots, C,D).(basolateral spots, C,D).Epithelial cell adhesionEpithelial cell adhesionmolecules are downmolecules are down--regulated,regulated,and as the apical region of theand as the apical region of the

cell shrinks, the apicalcell shrinks, the apicaljunctions decrease injunctions decrease incircumference and in strength,circumference and in strength,and eventually the cell pullsand eventually the cell pullsitself, or is pulled or pusheditself, or is pulled or pushedbeneath the surface and out ofbeneath the surface and out ofthe epithelium (Cthe epithelium (CE).E).


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Steps ofEMTSteps ofEMT Epithelial cell adhesionEpithelial cell adhesion

molecules are downmolecules are down--regulated,regulated,and as the apical region of theand as the apical region of thecell shrinks, the apicalcell shrinks, the apicaljunctions decrease injunctions decrease incircumference and in strength,circumference and in strength,

and eventually the cell pullsand eventually the cell pullsitself, or is pulled or pusheditself, or is pulled or pushedbeneath the surface and out ofbeneath the surface and out ofthe epithelium (Cthe epithelium (CE). In someE). In somecases the apical membrane iscases the apical membrane isthrown into microvilli orthrown into microvilli ormicrofolds as the apical regionmicrofolds as the apical region

of the cell decreases in area,of the cell decreases in area,and membrane may beand membrane may beinternalized (C). Molecules orinternalized (C). Molecules orwhole junctions of thewhole junctions of thejunctional complex may also bejunctional complex may also beremoved from the cell surfaceremoved from the cell surfaceand internalized as vesiclesand internalized as vesicles

(C).(C).


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Steps ofEMTSteps ofEMTWe envision two ways ofWe envision two ways ofremoving the cell from theremoving the cell from theepithelium. The apicalepithelium. The apicaljunctional complex breaks, thejunctional complex breaks, thecontiguity of the cell withcontiguity of the cell withepithelium is broken, and itepithelium is broken, and it

leaves the epitheliumleaves the epithelium(ingression) and a hole in its(ingression) and a hole in itsplace (C). Alternatively, theplace (C). Alternatively, theadjacent cells might bridgeadjacent cells might bridgeover the ingressing cell, form aover the ingressing cell, form ajunctional complex above it,junctional complex above it,

and provide physiological andand provide physiological andmechanical contiguity while themechanical contiguity while thecell ingresses (C ). Disarrayedcell ingresses (C ). Disarrayedpatches of junctions are oftenpatches of junctions are oftenfound on freshly ingressed cellsfound on freshly ingressed cells(C,C ).(C,C ).


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Steps ofEMTSteps ofEMT Other cytoskeletalOther cytoskeletal

changes also occur.changes also occur.Vimentin containingVimentin containingintermediate filamentsintermediate filamentsare formed in favor of theare formed in favor of the

cytokeratin intermediatecytokeratin intermediatefilaments of epithelialfilaments of epithelialcells, and the regulationcells, and the regulationof the cytoskeleton,of the cytoskeleton,protrusive activity, andprotrusive activity, and

contact and guidancecontact and guidancebehavior is altered to thebehavior is altered to themesenchymal pattern bymesenchymal pattern byas yet poorly understoodas yet poorly understoodmechanisms.mechanisms.


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Typical pattern of embryonicTypical pattern of embryonic

development in animalsdevelopment in animals

NOTE #1: Speaking here ofNOTE #1: Speaking here of

Metazoans. This process does notMetazoans. This process does notoccur in single celled organisms,occur in single celled organisms,fungi or plants, the latter two beingfungi or plants, the latter two beingunable to move their cells because ofunable to move their cells because of

the presence of a cell wallthe presence of a cell wall


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Animal DevelopmentAnimal Development -- II

Early cleavage results in a ball ofEarly cleavage results in a ball ofcells which, on cue, form tightcells which, on cue, form tightdesmosomal junctions and usually adesmosomal junctions and usually ahollow space, the blastocoel.hollow space, the blastocoel.

Thus the initial structure is anThus the initial structure is anepithelium folded into a ball.epithelium folded into a ball.


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Animal DevelopmentAnimal Development -- IIII

The second phase is the formation ofThe second phase is the formation ofa Triploblastic embryo.a Triploblastic embryo.

Three primary germ layersThree primary germ layersEctodermEctoderm

MesodermMesoderm

EndodermEndoderm

Process is called GastrulationProcess is called Gastrulation


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GastrulationGastrulation

Two processes involvedTwo processes involved

Epithelial sheet deforms as a unit toEpithelial sheet deforms as a unit toform the archenteron or primitive gutform the archenteron or primitive gut

A small number of cells at the baseA small number of cells at the base

or vegetal plate loose contact withor vegetal plate loose contact withneighbors, tear loose for Basalneighbors, tear loose for Basallamina and crawl into blastocoellamina and crawl into blastocoel


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Sea Urchin EMTSea Urchin EMT


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Amphibian EMTAmphibian EMT


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Surface and Cross SectionSurface and Cross Section


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Chicken EMTChicken EMT


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Chordate Neurulation EMTChordate Neurulation EMT


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EMT in TissuesEMT in Tissues

Epithelium IEpithelium I induces aninduces anEMTprocessEMTprocess inin epitheliumepitheliumIIII ((black arrowsblack arrows) through) throughthe secretion ofthe secretion ofinducersinducers((purple dotspurple dots). The). The

epithelium IIepithelium II--derivedderivedmesenchymal populationmesenchymal population((greengreen) is recruited by) is recruited byepithelium Iepithelium I ((greengreen--toto--blueblue--graded arrowsgraded arrows) and) anddifferentiatesdifferentiates ((blue cellsblue cells))

according to the molecularaccording to the molecularinformation arising frominformation arising fromthe inducing tissuethe inducing tissue ((redreddotsdots).).


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EMT and CancerEMT and Cancer

Occurrence of EMT during tumorOccurrence of EMT during tumorprogression allows benign tumors toprogression allows benign tumors toinfiltrate surrounding tissue andinfiltrate surrounding tissue andultimately metastasize to distantultimately metastasize to distantsitessites

We see EMT stages in pathologicalWe see EMT stages in pathologicalstaging of tumorsstaging of tumors


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EMT in Tumor ProgressionEMT in Tumor Progression


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EMT ofNBTII Cells and MouseEMT ofNBTII Cells and Mouse

GastrulationGastrulation


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TGF beta and Chick HeartTGF beta and Chick Heart


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Sarcomas and CarcinomasSarcomas and Carcinomas


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EMT and Colorectal CancerEMT and Colorectal Cancer


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EMTSignaling PathwaysEMTSignaling Pathways

Epithelial Mesenchymal Transition

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