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Neuralcrestcellsandaxonalspecificity1.Theneuralcrestandsomederivativesoftheneuralcrest2.Theneuralcrestcanbedividedintofourmainfunctionaldomains•Thetrunkneuralcrest•Thecranial(面部)neuralcrest•Thecardiac(心区)neuralcrest•Thevagal(迷走)andsacral(尾底)neuralcrestTheneuralcrestcellsoriginateatthedorsalmostregionoftheneuraltubeTheneuralcrestcellsgenerateanumberofdifferentiatedcelltypes•theneuronsandglialcells(胶质细胞)ofthesensory,sympathetic,andparasympatheticnervoussystems•theepinephrine-producing(medulla)cellsoftheadrenalgland(肾上腺髓质细胞)•thepigment-containingcellsoftheepidermis•manyoftheskeletalandconnectivetissuecomponentsofthehead.Table13.1SomederivativesoftheneuralcrestPeripheralnervoussystem(PNS)(外周神经系统)：includingsensoryganglia,sympatheticandparasympatheticganglia,Schwanncells(雪旺细胞),Neuroglialcells.Endocrineandparaendocrinederivatives(内分泌和旁分泌组织)：Calcitonin-secretingcells(降血钙素分泌细胞),CarotidbodytypeIcells(颈动脉一型体细胞).Pigmentcells(色素细胞)：Epidermalpigmentcells.Facialcartilageandbone(面部的骨骼和骨组织)：Facialandanteriorventralskullcartilageandbones.Connectivetissue(结缔组织)：Cornealendotheliumandstroma,Toothpapillae,Dermis,smoothmuscle,andadiposetissueofskinofheadandneck,Connectivetissueofsalivary,lachrymal,thymus,thyroid,andpituitaryglands，Connectivetissueandsmoothmuscleinarteriesofaorticarchorigin.`Regionsoftheneuralcrest.Thecranialneuralcrestmigratesintothebranchialarchesandthefacetoformthebonesandcartilageofthefaceandneck.Italsoproducespigmentandcranialnerves.Thevagalneuralcrest(nearsomites1–7)andthesacralneuralcrest(posteriortosomite28)formtheparasympatheticnervesofthegut.Thecardiacneuralcrestcellsarisefromtheneuralcrestbysomites1–3;theyarecriticalinmakingthedivisionbeeweentheaortaandthepulmonaryartery.Neuralcrestcellsofthetrunk(aboutsomite6throughthetail)makethesympatheticneurons,andasubsetofthese(atthelevelofsomites18–24)formthemedullaportionoftheadrenalgland.Thetrunkneuralcrest•Themechanismsoftrunkneuralcrestmigration1.Howismigrationinitiated?2.Howdothemigratoryagentsknowtherouteonwhichtotravel?3.Whatsignalsindicatethatthedestinationhasbeenreachedandthatmigrationshouldend?TheneuralcrestcellmigrationNeuralcrestcellsoriginatefromtheneuralfoldsthroughinteractionsoftheneuralplatewiththepresumptiveepidermis.Inculturesofembryonicchickectoderm,epidermiscaninduceneuralcrestformationintheneuralplatetowhichitisconnected.Thesecanbemimickedbyculturingneuralplatecellswithbonemorphogeneticproteins(骨形态发生蛋白)4and7(BMP4andBMP7),twoproteinsthatareknowntobesecretedbythepresumptiveepidermis.BMP4andBMP7inducetheexpressionoftheSlugproteinandtheRhoBproteininthecellsdestinedtobecomeneuralcrestTheRhoBproteinmaybeinvolvedinestablishingthecytoskeletalconditionsthatpromotemigration.TheSlugproteinistoactivatethefactorsthatdissociatethetightjunctionsbetweenthecells.N-cadherinisexpressedbeforetheneuralcrestcellsmigrationfromtheneuraltube.thiscelladhesionproteinisdownregulatedatthetimeofcellmigration,buttheybegintoexpressitagainastheyaggregatetoformthedorsalrootandsympatheticganglia.AllmigratingneuralcrestcellsexpressHNK-1(redstain),asinFigure13.2.TheRhoBprotein(greenstain)isexpressedincellsastheyleavetheneuralcrest.CellsexpressingbothHNK-1andRhoBappearyellow.•RecognitionofsurroundingextracellularmatricesTheextracellularmatrixmoleculesthatenableorforbidmigration.(这两类分子通过不同区域分布确定迁移路线)Theseproteinspromotesmigrationincludefibronectin,laminin,variouscollagenmolecules(胶原分子),andproteoglycans蛋白聚糖.Anotherproteinsimpedesmigration(theephrinproteins).Theseproteinsareexpressedintheposteriorsectionofeachsclerotome,andwherevertheyare,neuralcrestcellsdonotgoTheneuralcrestcellsrecognizetheephrinproteinsthroughtheircellsurfaceEphreceptors.Bindingtotheephrinsactivatesthetyrosinekinase(酪氨酸激酶)domainsoftheEphreceptors.thesekinasesprobablyphosphorylateproteinsthatinterferewiththeactincytoskeletonthatiscriticalforcellmigration.Chemotactic(趋化)andmaintenance(维持)factorsarealsoimportantinneuralcrestcellmigration.Stemcellfactoriscriticalinallowingtheneuralcrestcellsthatentertheskin,anditmayalsoserveasananti-apoptosis(抗凋亡)factorandachemotacticfactor.Ifstemcellfactorissecretedfromcellsthatdonotusuallysynthesizethisprotein(suchasthecheekepitheliumorfootpads),neuralcrestcellswillenterthoseregionsandbecomemelanocytes.Segmentalrestrictionofneuralcrestcellsandmotorneuronsbytheephrinproteinsofthesclerotome.(A)Negativecorrelationbetweenregionsofephrininthesclerotome(darkbluestain,left)andneuralcrestcellmigration(greenHNK-1stain,right).(B)Whenneuralcrestcellsareplatedonfibronectin-containingmatriceswithalternatingstripesofephrin,theybindtothoseregionslackingephrin.(C)Compositeschemeshowingmigrationofspinalcordneuralcrestcellsandmotorneuronsthroughtheephrin-deficientanteriorregionsofthesclerotomes.(Forclarity,theneuralcrestcellsandmotorneuronsareeachdepictedononlyonesideofthespinalcord•ThepluripotencyoftrunkneuralcrestcellsAsingleneuralcrestcellcandifferentiateintoanyofseveraldifferentcelltypes,dependingonitslocationwithintheembryo.Forexample,theparasympatheticneuronsformedbythevagal(neck)neuralcrestce