第十五章-细胞分化与胚胎发育-北大陈建国细胞生物学

1第15章细胞分化和胚胎发育CelldifferentiationandembryonicdevelopmentThefouressentialcellprocessesthatallowamulticellularorganismtobemadewhichproducesmanycellsfromone;whichcoordinatethebehaviorofeachcellwiththatofitsneighbors;ordifferentiation,whichcreatescellswithdifferentcharacteristicsatdifferentpositions；whichrearrangesthecellstoformstructuredtissuesandorgans.215-1.UNIVERSALMECHANISMSOFANIMALDEVELOPMENTHomologousproteinsfunctioninginterchangeablyinthedevelopmentofmiceandflies4ThescanningelectronmicrographsshowapatchofeyetissueonthelegofaflyresultingfrommisexpressionofDrosophilaEyeless(top)andofsquidPax6(bottom).Therightpanelshows,atlowermagnification,theentireeyeofanormalDrosophila5AnimalsShareSomeBasicAnatomicalFeaturesSeaurchingastrulation.Afertilizedeggdividestoproduceablastula—ahollowsphereofepithelialcellssurroundingacavity.Then,intheprocessofgastrulation,someofthecellstuckintotheinteriortoformthegutandotherinternaltissues.(A)Scanningelectronmicrographshowingtheinitialintuckingoftheepithelium.6(B)Agroupofcellsbreakloosefromtheepitheliumtobecomemesoderm.(C)Thesecellsthencrawlovertheinnerfaceofthewalloftheblastula.(D)Meanwhile,epitheliumiscontinuingtotuckinwardtobecomeendoderm.(EandF)Theinvaginatingendodermextendsintoalongguttube.(G)Theendoftheguttubemakescontactwiththewalloftheblastulaatthesiteofthefuturemouthopening.Heretheectodermandendodermwillfuseandaholewillform.78Thebasicanimalbodyplan,withasheetofectodermontheoutside,atubeofendodermontheinside,andmesodermsandwichedbetweenthem.9MulticellularAnimalsAreEnrichedinProteinsMediatingCellInteractionsandGeneRegulationC.elegans:20,000genesDrosophila:14,000genesHuman:25,000genesAbout50%ofthegenesineachofthesespecieshaveclearlyrecognizablehomologsinoneorbothoftheothertwospeciesMulticellularanimalAsmanyas2000C.elegansgenesencodecellsurfacereceptors,celladhesionproteins,andionchannelsthatareeithernotpresentinyeastorpresentinmuchsmallernumbers.generegulatoryproteins:theseDNA-bindingproteinsaremuchmorenumerousintheC.elegansgenomethaninyeast.Thebasichelix–loop–helixfamilyhas41membersinC.elegans,84inDrosophila,131inhumansandonly7inyeast,10RegulatoryDNADefinestheProgramofDevelopmentHowregulatoryDNAdefinesthesuccessionofgeneexpressionpatternsindevelopment11Celllineagetracingintheearlychickembryo.Thepicturesinthetoprowareatlowmagnificationandshowthewholeembryo;thepicturesbelowaredetails,showingthedistributionoflabeledcells.Thetracingexperimentrevealscomplexanddramaticcellrearrangements.ManipulationoftheEmbryoRevealstheInteractionsBetweenItsCells12Somestrikingresultsobtainedbyexperimentalembryology13StudiesofMutantAnimalsIdentifytheGenesThatControlDevelopmentalProcesses.ACellMakesDevelopmentalDecisionsLongBeforeItShowsaVisibleChange.14ACellMakesDevelopmentalDecisionsLongBeforeItShowsaVisibleChangeProspectivethightissuegraftedintothetipofachickwingbudformstoes.(AfterJ.W.Saundersetal.,Dev.Biol.1:281–301,1959.WithpermissionfromAcademicPress.)15Chickembryosat6daysofincubation,showingthelimbbudsstainedbyinsituhybridizationwithprobestodetectexpressionoftheTbx4,Tbx5,andPitx1genes,allcodingforrelatedgeneregulatoryproteins.ThecellsexpressingTbx5willformawing;thoseexpressingTbx4andPitx1willformaleg.Pitx1,whenartificiallymisexpressedinthewingbud,causesthelimbtodevelopwithleg-likecharacteristics.16InductiveSignalsCanCreateOrderlyDifferencesBetweenInitiallyIdenticalCells17SomeSignalProteinsThatAreUsedOverandOverAgainasInducersinAnimalDevelopment18SisterCellsCanBeBornDifferentbyanAsymmetricCellDivisionCentrosomesandNeuralStemCellsThedominantforceofCentrobinincentrosomeasymmetry19apical(yellow)andbasal(pink)corticalcrescentsareestablishedCentrobin(CNB)2021PositiveFeedbackCanCreateAsymmetryWhereThereWasNoneBeforeGenesisofasymmetrythroughpositivefeedback.Inthisexample,twocellsinteract,eachproducingasubstanceXthatactsontheothercelltoinhibititsproductionofX,aneffectknownaslateralinhibition.22MorphogensAreLong-RangeInducersThatExertGradedEffectsSonichedgehogasamorphogeninchicklimbdevelopment.(A)ExpressionoftheSonichedgehoggeneina4-daychickembryo,shownbyinsituhybridization.Thegeneisexpressedinthemidlineofthebodyandattheposteriorborderofeachofthetwowingbuds.Sonichedgehogproteinspreadsoutfromthesesources.(B)Normalwingdevelopment.(C)Agraftoftissuefromthepolarizingregioncausesamirror-imageduplicationofthepatternofthehostwing.ThetypeofdigitthatdevelopsisthoughttobedictatedbythelocalconcentrationofSonichedgehogprotein;differenttypesofdigit(labeled2,3,and4)thereforeformaccordingtotheirdistancefromasourceofSonichedgehog.23ExtracellularInhibitorsofSignalMoleculesShapetheResponsetotheInducer24DevelopmentalSignalsCanSpreadThroughTissueinSeveralDifferentWaysFigure22-16MolecularBiologyoftheCell(©GarlandScience2008)25InitialPatternsAreEstablishedinSmallFieldsofCellsandRefinedbySequentialInductionastheEmbryoGrows2615-2.CAENORHABDITISELEGANS:DEVELOPMENTFROMTHEPERSPECTIVEOFTHEINDIVIDUALCELLAsanadult,C.elegansconsistsofonlyabout1000somaticcellsand1000–2000germcells(exactly959somaticcellnucleiplusabout2000germcellsinonesex;exactly1031somaticcellnucleiplusabout1000germcellsintheother)27CellFatesintheDevelopingNematodeAreAlmostPerfectlyPredictable28ProductsofMaternal-EffectGenesOrganizetheAsymmetricDivisionoftheEggAsymmetricdivisionssegregatingPgranulesintothefoundercelloftheC.elegansgermline.Themicrographsintheupperrowshowthepatternofcelldivisions,withcellnucleistainedbluewithaDNA-specificfluorescentdye;belowarethesamecellsstainedwithanantibodyagainstPgranules.Thesesmallaredistributedrandomlythroughoutthecytoplasmintheunfertilizedegg(notshown).Afterfertilization,ateachcelldivisionuptothe16-cellstage,boththeyandtheintracellularmachinerythatregulatestheirasymmetriclocalizationaresegregatedintoasingledaughtercell.Parproteins29ProgressivelyMoreComplexPatternsAreCreatedbyCell–CellInteractionsThepatternofcelldivisionsintheearlyC.elegansembryo,indicatingthenamesandfatesoftheindividualcellsNotchCellsignalingpathwayscontrollingassignmentofdifferentcharacterstothecellsinafour-cellnematodeembryo30SelectedCellsDiebyApoptosisasPartoftheProgramofDevelopmentThecontrolofcellnumbersindevelopmentdependsoncelldeathaswellascelldivision.AC.eleganshermaphroditegenerates1030somaticcellnucleiinthecourseofitsdevelopment,but131ofthecellsdie.3115-3.DROSOPHILAANDTHEMOLECULARGENETICSOFPATTERNFORMATION:GENESISOFTHEBODYPLANCellnumber;Genes;noncodingDNA;geneduplicationsofvertebrategenomes32TheInsectBodyIsConstructedasaSeriesofSegmentalUnits33TheoriginsoftheDrosophilabodysegmentsduringembryonicdevelopment.34ThesegmentsoftheDrosophilalarvaandtheircorrespondencewithregionsoftheblastoderm.35DevelopmentoftheDrosophilaeggfromfertilizationtothecellularblastodermstage.(A)Schematicdrawings.(B)Surfaceview—anoptical-sectionphotographofblastodermnucleiundergoingmitosisatthetransitionfromthesyncytialtothecellularblastodermstage.Actinisstainedgreen,chromosomesorange.36FatemapofaDrosophilaembryoatthecellularblastodermstage37GeneticScreensDefineGroupsofGenesRequiredforSpecificAspectsofEarlyPatterningThedomainsoftheanterior,posterior,andterminalsystemsofegg-polaritygenes.Upperdiagramsshowthefatesofthedifferentregionsoftheegg/earlyembryoandindicate(inwhite)thepartsthatfailtodevelopiftheanterior,posterior,orterminalsystemisdefective.Middlerowshowsschematicallytheappearanceofanormallarvaandofmutantlarvaethataredefectiveinageneoftheanteriorsystem(Bicoid),oftheposteriorsystem(Nanos),oroftheterminalsystem(Torso).Thebottomrowofdrawingsshowstheappearancesoflarvaeinwhichnoneoronlyoneofthethreegenesystemsisfunctional.Inactivationofaparticulargenesystemcauseslossofthecorrespondingsetofbodystructures;thebodypartsthatformcorrespondtothegenesystemsthatremainfunctional.Notethatlarvaewithadefectintheanteriorsystemcanstillformterminalstructuresattheiranteriorend,buttheseareofthetypenormallyfoundattherearendofthebodyratherthanthefrontofthehead.38InteractionsoftheOocyteWithItsSurroundingsDefinetheAxesoftheEmbryo:theRoleoftheEgg-PolarityGenes39Theorganizationofthefouregg-polaritygradientsystems(maternal-effectgenes).ThereceptorsTollandTorsoaredistributedalloverthemembrane;thecoloringinthediagramsontherightindicateswheretheybecomeactivatedbyextracellularligands.TheRoleoftheEgg-PolarityGenes40TheDorsoventralSignalingGenesCreateaGradientofaNuclearGeneRegulatoryProteinTheconcentrationgradientofDorsalprotein(likeNF-kabaB)inthenucleioftheblastoderm,asrevealedbyanantibody.Dorsally,theproteinispresentinthecytoplasmandabsentfromthenuclei;ventrally,itisdepletedinthecytoplasmandconcentratedinthenuclei(TollreceptorontheventralsideoftheeggcontrolsthedistributionofDorsal).41Morphogengradientspatterningthedorsoventralaxisoftheembryo.(A)ThegradientofDorsalproteindefinesthreebroadterritoriesofgeneexpression,markedherebytheexpressionofthreerepresentativegenes—Dpp,Sog,andTwist.(B)Slightlylater,thecellsexpressingDppandSogsecrete,respectively,thesignalproteinsDpp(aTGFbfamilymember)andSog(anantagonistofDpp).Thesetwoproteinsdiffuseandinteractwithoneanother(andwithcertainotherfactors)tosetupagradientofDppactivitythatguidesamoredetailedpatterningprocess.DppandSogSetUpaSecondaryMorphogenGradienttoRefinethePatternoftheDorsalPartoftheEmbryo42OriginofthemesodermfromcellsexpressingTwist.Embryoswerefixedatsuccessivestages,crosssectioned,andstainedwithanantibodyagainsttheTwistprotein,ageneregulatoryproteinofthebHLHfamily.ThecellsthatexpressTwistmoveintotheinterioroftheembryotoformmesoderm.TheDorsoventralSignalingGenesCreateaGradientofaNuclearGeneRegulatoryProtein43TheInsectDorsoventralAxisCorrespondstotheVertebrateVentrodorsalAxisDpp:amemberoftheTGFbsuperfamilyofsignalmoleculesthatisalsoimportantinvertebrates;Sog:ahomologofthevertebrateproteinchordin.ItisstrikingthataDpphomolog,BMP4,andchordinworktogetherinvertebratesinthesamewayasdoDppandSoginDrosophila.4445ThreeClassesofSegmentationGenesRefinetheAnterior–PosteriorMaternalPatternandSubdividetheEmbryo间隙基因成对控制基因体节极性基因Examplesofthephenotypesofmutationsaffectingthethreetypesofsegmentationgenes46TheLocalizedExpressionofSegmentationGenesIsRegulatedbyaHierarchyofPositionalSignalsTheregulatoryhierarchyofegg-polarity,gap,segmentation,andhomeoticselectorgenes.Thephotographsshowexpressionpatternsofrepresentativeexamplesofgenesineachcategory,47484950HOMEOTICSELECTORGENESANDTHEPATTERNINGOFTHEANTEROPOSTERIORAXISTheHoxCodeSpecifiesAnterior–PosteriorDifferencesAhomeoticmutation.TheflyshownhereisanAntennapediamutant.Whatisthebasicconstructionmechanismcommontoalltheobjectsofthegivenclass?Howisthismechanismmodifiedtogivetheobservedvariations?Figure22-43MolecularBiologyoftheCell(©GarlandScience2008)51Figure22-44MolecularBiologyoftheCell(©GarlandScience2008)52Figure22-45MolecularBiologyoftheCell(©GarlandScience2008)53Figure22-46MolecularBiologyoftheCell(©GarlandScience2008)54Figure22-47MolecularBiologyoftheCell(©GarlandScience2008)55Figure22-48MolecularBiologyoftheCell(©GarlandScience2008)56Figure22-49MolecularBiologyoftheCell(©GarlandScience2008)57Figure22-50aMolecularBiologyoftheCell(©GarlandScience2008)58Figure22-50bMolecularBiologyoftheCell(©GarlandScience2008)59Figure22-51MolecularBiologyoftheCell(©GarlandScience2008)60Figure22-52aMolecularBiologyoftheCell(©GarlandScience2008)61Figure22-52bMolecularBiologyoftheCell(©GarlandScience2008)62Figure22-53MolecularBiologyoftheCell(©GarlandScience2008)63Figure22-54aMolecularBiologyoftheCell(©GarlandScience2008)64Figure22-54bMolecularBiologyoftheCell(©GarlandScience2008)65Figure22-55MolecularBiologyoftheCell(©GarlandScience2008)66Figure22-56MolecularBiologyoftheCell(©GarlandScience2008)67Figure22-57MolecularBiologyoftheCell(©GarlandScience2008)68Figure22-57aMolecularBiologyoftheCell(©GarlandScience2008)69Figure22-57bMolecularBiologyoftheCell(©GarlandScience2008)70Figure22-58MolecularBiologyoftheCell(©GarlandScience2008)71Figure22-59MolecularBiologyoftheCell(©GarlandScience2008)72Figure22-60aMolecularBiologyoftheCell(©GarlandScience2008)73Figure22-60bMolecularBiologyoftheCell(©GarlandScience2008)74Figure22-61MolecularBiologyoftheCell(©GarlandScience2008)75Figure22-62MolecularBiologyoftheCell(©GarlandScience2008)76Figure22-63MolecularBiologyoftheCell(©GarlandScience2008)77Figure22-64aMolecularBiologyoftheCell(©GarlandScience2008)78Figure22-64bMolecularBiologyoftheCell(©GarlandScience2008)79Figure22-65MolecularBiologyoftheCell(©GarlandScience2008)80Figure22-66MolecularBiologyoftheCell(©GarlandScience2008)81Figure22-66aMolecularBiologyoftheCell(©GarlandScience2008)82Figure22-66bMolecularBiologyoftheCell(©GarlandScience2008)838415-4.CELLMOVEMENTSANDTHESHAPINGOFTHEVERTEBRATEBODY85TheXenopusegganditsasymmetries.(A)Sideviewofaneggphotographedjustbeforefertilization.86ThePolarityoftheAmphibianEmbryoDependsonthePolarityoftheEggTheasymmetricdistributionofmoleculesinsidetheegg,andhowthischangesfollowingfertilizationsoastodefineadorsoventralaswellasananimal–vegetalasymmetry.Fertilization,throughareorganizationofthemicrotubulecytoskeleton,triggersarotationoftheeggcortex(alayerafewmmdeep)throughabout30°relativetothecoreoftheegginadirectiondeterminedbythesiteofspermentry.Somecomponentsarecarriedstillfurthertothefuturedorsalsidebyactivetransportalongmicrotubules.TheresultingdorsalconcentrationofWnt11mRNAleadstodorsalproductionoftheWnt11signalproteinanddefinesthedorsoventralpolarityofthefutureembryo.Figure22-69MolecularBiologyoftheCell(©GarlandScience2008)87ThestagesofcleavageinXenopus.Thecleavagedivisionsrapidlysubdividetheeggintomanysmallercells.Allthecellsdividesynchronouslyforthefirst12cleavages,butthedivisionsareasymmetric,sothatthelower,vegetalcells,encumberedwithyolk,arefewerandlarger.88Theoriginsofthethreegermlayerscanbetracedbacktodistinctblastomeresoftheembryoinitsearlycleavagestages.Theendodermderivesfromthemostvegetalblastomeres,theectodermfromthemostanimal,andthemesodermfromamiddlesetthatcontributealsotoendodermandectoderm.Thecoloringineachpictureisthemoreintense,thehighertheproportionofcellprogenythatwillcontributetothegivengermlayer.89Theblastula.Intheoutermostregionsoftheembryo,tightjunctionsbetweentheblastomeresbegintocreateanepithelialsheetthatisolatestheinterioroftheembryofromtheexternalmedium.Na+ispumpedacrossthissheetintothespacesintheinterioroftheembryo,andwaterfollowsintothesespacesbecauseoftheresultingosmoticpressuregradient.Asaresult,theintercellularcrevicesinsidetheembryoenlargetoformasinglecavity,theblastocoel(囊胚腔).InXenopusthewalloftheblastocoelisseveralcellsthick,andonlytheoutermostcellsaretightlyboundtogetherasanepithelium.GastrulationTransformsaHollowBallofCellsintoaThree-LayeredStructurewithaPrimitiveGut90Acrosssectionthroughthetrunkofanamphibianembryoaftertheendofgastrulation,showingthearrangementofendodermal,mesodermalandectodermaltissues.Theendodermwillformtheepithelialliningofthegut,andmanyassociatedglands.Thesalivaryglands,theliver,thepancreas,thetrachea,andthelungs.Theendodermformsonlytheepithelialcomponentsofthesestructures—theliningofthegutandthesecretorycellsofthepancreas,forexample.Themesodermgivesrisetotheconnectivetissues—atfirsttotheloose,space-filling,three-dimensionalmeshofcellsintheembryoknownasmesenchyme,andultimatelytocartilage,bone,andfibroustissue,includingthedermis(theinnerlayeroftheskin).Themesodermalsoformsthemuscles,theentirevascularsystem—includingtheheart,thebloodvessels,andthebloodcells—andthetubules,ducts,andsupportingtissuesofthekidneysandgonads.Theectodermwillformtheandepidermalappendages.Itwillalsogiverisetothewholeofthenervoussystem,thesensorycellsofthenose,theear,theeye,andothersenseorgans.9192Sortingout.Cellsfromdifferentpartsofanearlyamphibianembryowillsortoutaccordingtotheirorigins.Intheclassicalexperimentshownhere,mesodermcells(green),neuralplatecells(blue),andepidermalcells(red)havebeendisaggregatedandthenreaggregatedinarandommixture.Theysortoutintoanarrangementreminiscentofanormalembryo,witha“neuraltube”internally,epidermisexternally,andmesoderminbetween.93NeuraltubeformationinXenopus94Thebendingofanepitheliumthroughcellshapechangesmediatedbymicrotubulesandactinfilaments.Thediagramisbasedonobservationsofneurulationinnewtsandsalamanders,wheretheepitheliumisonlyonecelllayerthick.Astheapicalendsofthecellsbecomenarrower,theiruppersurfacemembranebecomespuckered.9515-5.THEMOUSETheearlystagesofmousedevelopment.Thezonapellucidaisajellycapsulefromwhichtheembryoescapesafterafewdays,allowingittoimplantinthewalloftheuterus.96Scanningelectronmicrographsoftheearlymouseembryo97Aprocedureforcreatingachimericmouse.Twomorulaeofdifferentgenotypesarecombined.98MakingachimericmousewithEScells.TheculturedEScellscancombinewiththecellsofanormalblastocysttoformahealthychimericmouse,andcancontributetoanyofitstissues,includingthegermline.ThustheEScellsaretotipotent.99Branchingmorphogenesisofthelung.(A)HowFGF10andSonichedgehogarethoughttoinducethegrowthandbranchingofthebudsofthebronchialtree.Manyothersignalmolecules,suchasBMP4,arealsoexpressedinthissystem,andthesuggestedbranchingmechanismisonlyoneofseveralpossibilities.InteractionsBetweenanEpitheliumandMesenchymeGenerateBranchingTubularStructures100Acastoftheadulthumanbronchialtree,preparedbyinjectingresinintotheairways;resinsofdifferentcolorshavebeeninjectedintodifferentbranchesofthetree.10115-6.NEURALDEVELOPMENT102Thecentralchallengeofneuraldevelopmentistoexplainhowtheaxonsanddendritesgrowout,findtheirrightpartners,andsynapsewiththemselectivelytocreateafunctionalnetworkThecomplexorganizationofnervecellconnections.10