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Celldifferentiationandembryonicdevelopment,Thefouressentialcellprocessesthatallowamulticellularorganismtobemade,whichproducesmanycellsfromone;,whichcoordinatethebehaviorofeachcellwiththatofitsneighbors;,ordifferentiation,whichcreatescellswithdifferentcharacteristicsatdifferentpositions；,whichrearrangesthecellstoformstructuredtissuesandorgans.,2,15-1.UNIVERSALMECHANISMSOFANIMALDEVELOPMENT,Homologousproteinsfunctioninginterchangeablyinthedevelopmentofmiceandflies,4,ThescanningelectronmicrographsshowapatchofeyetissueonthelegofaflyresultingfrommisexpressionofDrosophilaEyeless(top)andofsquidPax6(bottom).Therightpanelshows,atlowermagnification,theentireeyeofanormalDrosophila,5,AnimalsShareSomeBasicAnatomicalFeatures,Seaurchingastrulation.Afertilizedeggdividestoproduceablastulaahollowsphereofepithelialcellssurroundingacavity.Then,intheprocessofgastrulation,someofthecellstuckintotheinteriortoformthegutandotherinternaltissues.(A)Scanningelectronmicrographshowingtheinitialintuckingoftheepithelium.,6,(B)Agroupofcellsbreakloosefromtheepitheliumtobecomemesoderm.(C)Thesecellsthencrawlovertheinnerfaceofthewalloftheblastula.(D)Meanwhile,epitheliumiscontinuingtotuckinwardtobecomeendoderm.(EandF)Theinvaginatingendodermextendsintoalongguttube.(G)Theendoftheguttubemakescontactwiththewalloftheblastulaatthesiteofthefuturemouthopening.Heretheectodermandendodermwillfuseandaholewillform.,7,8,Thebasicanimalbodyplan,withasheetofectodermontheoutside,atubeofendodermontheinside,andmesodermsandwichedbetweenthem.,9,MulticellularAnimalsAreEnrichedinProteinsMediatingCellInteractionsandGeneRegulation,C.elegans:20,000genesDrosophila:14,000genesHuman:25,000genes,About50%ofthegenesineachofthesespecieshaveclearlyrecognizablehomologsinoneorbothoftheothertwospecies,Multicellularanimal,Asmanyas2000C.elegansgenesencodecellsurfacereceptors,celladhesionproteins,andionchannelsthatareeithernotpresentinyeastorpresentinmuchsmallernumbers.generegulatoryproteins:theseDNA-bindingproteinsaremuchmorenumerousintheC.elegansgenomethaninyeast.,Thebasichelixloophelixfamilyhas41membersinC.elegans,84inDrosophila,131inhumansandonly7inyeast,10,RegulatoryDNADefinestheProgramofDevelopment,HowregulatoryDNAdefinesthesuccessionofgeneexpressionpatternsindevelopment,11,Celllineagetracingintheearlychickembryo.Thepicturesinthetoprowareatlowmagnificationandshowthewholeembryo;thepicturesbelowaredetails,showingthedistributionoflabeledcells.Thetracingexperimentrevealscomplexanddramaticcellrearrangements.,ManipulationoftheEmbryoRevealstheInteractionsBetweenItsCells,12,Somestrikingresultsobtainedbyexperimentalembryology,13,StudiesofMutantAnimalsIdentifytheGenesThatControlDevelopmentalProcesses.ACellMakesDevelopmentalDecisionsLongBeforeItShowsaVisibleChange.,14,ACellMakesDevelopmentalDecisionsLongBeforeItShowsaVisibleChange,Prospectivethightissuegraftedintothetipofachickwingbudformstoes.(AfterJ.W.Saundersetal.,Dev.Biol.1:281301,1959.WithpermissionfromAcademicPress.),15,Chickembryosat6daysofincubation,showingthelimbbudsstainedbyinsituhybridizationwithprobestodetectexpressionoftheTbx4,Tbx5,andPitx1genes,allcodingforrelatedgeneregulatoryproteins.ThecellsexpressingTbx5willformawing;thoseexpressingTbx4andPitx1willformaleg.Pitx1,whenartificiallymisexpressedinthewingbud,causesthelimbtodevelopwithleg-likecharacteristics.,16,InductiveSignalsCanCreateOrderlyDifferencesBetweenInitiallyIdenticalCells,17,SomeSignalProteinsThatAreUsedOverandOverAgainasInducersinAnimalDevelopment,18,SisterCellsCanBeBornDifferentbyanAsymmetricCellDivision,CentrosomesandNeuralStemCells,ThedominantforceofCentrobinincentrosomeasymmetry,19,apical(yellow)andbasal(pink)corticalcrescentsareestablished,Centrobin(CNB),20,21,PositiveFeedbackCanCreateAsymmetryWhereThereWasNoneBefore,Genesisofasymmetrythroughpositivefeedback.Inthisexample,twocellsinteract,eachproducingasubstanceXthatactsontheothercelltoinhibititsproductionofX,aneffectknownaslateralinhibition.,22,MorphogensAreLong-RangeInducersThatExertGradedEffects,Sonichedgehogasamorphogeninchicklimbdevelopment.(A)ExpressionoftheSonichedgehoggeneina4-daychickembryo,shownbyinsituhybridization.Thegeneisexpressedinthemidlineofthebodyandattheposteriorborderofeachofthetwowingbuds.Sonichedgehogproteinspreadsoutfromthesesources.(B)Normalwingdevelopment.(C)Agraftoftissuefromthepolarizingregioncausesamirror-imageduplicationofthepatternofthehostwing.ThetypeofdigitthatdevelopsisthoughttobedictatedbythelocalconcentrationofSonichedgehogprotein;differenttypesofdigit(labeled2,3,and4)thereforeformaccordingtotheirdistancefromasourceofSonichedgehog.,23,ExtracellularInhibitorsofSignalMoleculesShapetheResponsetotheInducer,24,DevelopmentalSignalsCanSpreadThroughTissueinSeveralDifferentWays,Figure22-16MolecularBiologyoftheCell(GarlandScience2008),25,InitialPatternsAreEstablishedinSmallFieldsofCellsandRefinedbySequentialInductionastheEmbryoGrows,26,15-2.CAENORHABDITISELEGANS:DEVELOPMENTFROMTHEPERSPECTIVEOFTHEINDIVIDUALCELL,Asanadult,C.elegansconsistsofonlyabout1000somaticcellsand10002000germcells(exactly959somaticcellnucleiplusabout2000germcellsinonesex;exactly1031somaticcellnucleiplusabout1000germcellsintheother),27,CellFatesintheDevelopingNematodeAreAlmostPerfectlyPredictable,Thelineagetreeforthecellsthatformthegut(theintestine)ofC.elegans,28,ProductsofMaternal-EffectGenesOrganizetheAsymmetricDivisionoftheEgg,AsymmetricdivisionssegregatingPgranulesintothefoundercelloftheC.elegansgermline.Themicrographsintheupperrowshowthepatternofcelldivisions,withcellnucleistainedbluewithaDNA-specificfluorescentdye;belowarethesamecellsstainedwithanantibodyagainstPgranules.Thesesmallaredistributedrandomlythroughoutthecytoplasmintheunfertilizedegg(notshown).Afterfertilization,ateachcelldivisionuptothe16-cellstage,boththeyandtheintracellularmachinerythatregulatestheirasymmetriclocalizationaresegregatedintoasingledaughtercell.,Parproteins,29,ProgressivelyMoreComplexPatternsAreCreatedbyCellCellInteractions,ThepatternofcelldivisionsintheearlyC.elegansembryo,indicatingthenamesandfatesoftheindividualcells,Notch,Cellsignalingpathwayscontrollingassignmentofdifferentcharacterstothecellsinafour-cellnematodeembryo,30,SelectedCellsDiebyApoptosisasPartoftheProgramofDevelopment,Thecontrolofcellnumbersindevelopmentdependsoncelldeathaswellascelldivision.AC.eleganshermaphroditegenerates1030somaticcellnucleiinthecourseofitsdevelopment,but131ofthecellsdie.,31,15-3.DROSOPHILAANDTHEMOLECULARGENETICSOFPATTERNFORMATION:GENESISOFTHEBODYPLAN,Cellnumber;Genes;noncodingDNA;geneduplicationsofvertebrategenomes,32,TheInsectBodyIsConstructedasaSeriesofSegmentalUnits,33,TheoriginsoftheDrosophilabodysegmentsduringembryonicdevelopment.,34,ThesegmentsoftheDrosophilalarvaandtheircorrespondencewithregionsoftheblastoderm.,35,DevelopmentoftheDrosophilaeggfromfertilizationtothecellularblastodermstage.(A)Schematicdrawings.(B)Surfaceviewanoptical-sectionphotographofblastodermnucleiundergoingmitosisatthetransitionfromthesyncytialtothecellularblastodermstage.Actinisstainedgreen,chromosomesorange.,36,FatemapofaDrosophilaembryoatthecellularblastodermstage,37,GeneticScreensDefineGroupsofGenesRequiredforSpecificAspectsofEarlyPatterning,Thedomainsoftheanterior,posterior,andterminalsystemsofegg-polaritygenes.Upperdiagramsshowthefatesofthedifferentregionsoftheegg/earlyembryoandindicate(inwhite)thepartsthatfailtodevelopiftheanterior,posterior,orterminalsystemisdefective.Middlerowshowsschematicallytheappearanceofanormallarvaandofmutantlarvaethataredefectiveinageneoftheanteriorsystem(Bicoid),oftheposteriorsystem(Nanos),oroftheterminalsystem(Torso).Thebottomrowofdrawingsshowstheappearancesoflarvaeinwhichnoneoronlyoneofthethreegenesystemsisfunctional.Inactivationofaparticulargenesystemcauseslossofthecorrespondingsetofbodystructures;thebodypartsthatformcorrespondtothegenesystemsthatremainfunctional.Notethatlarvaewithadefectintheanteriorsystemcanstillformterminalstructuresattheiranteriorend,buttheseareofthetypenormallyfoundattherearendofthebodyratherthanthefrontofthehead.,38,InteractionsoftheOocyteWithItsSurroundingsDefinetheAxesoftheEmbryo:theRoleoftheEgg-PolarityGenes,39,Theorganizationofthefouregg-polaritygradientsystems(maternal-effectgenes).ThereceptorsTollandTorsoaredistributedalloverthemembrane;thecoloringinthediagramsontherightindicateswheretheybecomeactivatedbyextracellularligands.,TheRoleoftheEgg-PolarityGenes,40,TheDorsoventralSignalingGenesCreateaGradientofaNuclearGeneRegulatoryProtein,TheconcentrationgradientofDorsalprotein(likeNF-kabaB)inthenucleioftheblastoderm,asrevealedbyanantibody.Dorsally,theproteinispresentinthecytoplasmandabsentfromthenuclei;ventrally,itisdepletedinthecytoplasmandconcentratedinthenuclei(TollreceptorontheventralsideoftheeggcontrolsthedistributionofDorsal).,41,Morphogengradientspatterningthedorsoventralaxisoftheembryo.(A)ThegradientofDorsalproteindefinesthreebroadterritoriesofgeneexpression,markedherebytheexpressionofthreerepresentativegenesDpp,Sog,andTwist.(B)Slightlylater,thecellsexpressingDppandSogsecrete,respectively,thesignalproteinsDpp(aTGFbfamilymember)andSog(anantagonistofDpp).Thesetwoproteinsdiffuseandinteractwithoneanother(andwithcertainotherfactors)tosetupagradientofDppactivitythatguidesamoredetailedpatterningprocess.,DppandSogSetUpaSecondaryMorphogenGradienttoRefinethePatternoftheDorsalPartoftheEmbryo,42,OriginofthemesodermfromcellsexpressingTwist.Embryoswerefixedatsuccessivestages,crosssectioned,andstainedwithanantibodyagainsttheTwistprotein,ageneregulatoryproteinofthebHLHfamily.ThecellsthatexpressTwistmoveintotheinterioroftheembryotoformmesoderm.,TheDorsoventralSignalingGenesCreateaGradientofaNuclearGeneRegulatoryProtein,43,TheInsectDorsoventralAxisCorrespondstotheVertebrateVentrodorsalAxis,Dpp:amemberoftheTGFbsuperfamilyofsignalmoleculesthatisalsoimportantinvertebrates;Sog:ahomologofthevertebrateproteinchordin.ItisstrikingthataDpphomolog,BMP4,andchordinworktogetherinvertebratesinthesamewayasdoDppandSoginDrosophila.,44,45,ThreeClassesofSegmentationGenesRefinetheAnteriorPosteriorMaternalPatternandSubdividetheEmbryo,间隙基因成对控制基因体节极性基因,Examplesofthephenotypesofmutationsaffectingthethreetypesofsegmentationgenes,46,TheLocalizedExpressionofSegmentationGenesIsRegulatedbyaHierarchyofPositionalSignals,Theregulatoryhierarchyofegg-polarity,gap,segmentation,andhomeoticselectorgenes.Thephotographsshowexpressionpatternsofrepresentativeexamplesofgenesineachcategory,47,48,49,50,HOMEOTICSELECTORGENESANDTHEPATTERNINGOFTHEANTEROPOSTERIORAXIS,TheHoxCodeSpecifiesAnteriorPosteriorDifferences,Ahomeoticmutation.TheflyshownhereisanAntennapediamutant.,Whatisthebasicconstructionmechanismcommontoalltheobjectsofthegivenclass?Howisthismechanismmodifiedtogivetheobservedvariations?,Figure22-43MolecularBiologyoftheCell(GarlandScience2008),51,Figure22-44MolecularBiologyoftheCell(GarlandScience2008),52,Figure22-45MolecularBiologyoftheCell(GarlandScience2008),53,Figure22-46MolecularBiologyoftheCell(GarlandScience2008),54,Figure22-47MolecularBiologyoftheCell(GarlandScience2008),55,Figure22-48MolecularBiologyoftheCell(GarlandScience2008),56,Figure22-49MolecularBiologyoftheCell(GarlandScience2008),57,Figure22-50aMolecularBiologyoftheCell(GarlandScience2008),58,Figure22-50bMolecularBiologyoftheCell(GarlandScience2008),59,Figure22-51MolecularBiologyoftheCell(GarlandScience2008),60,Figure22-52aMolecularBiologyoftheCell(GarlandScience2008),61,Figure22-52bMolecularBiologyoftheCell(GarlandScience2008),62,Figure22-53MolecularBiologyoftheCell(GarlandScience2008),63,Figure22-54aMolecularBiologyoftheCell(GarlandScience2008),64,Figure22-54bMolecularBiologyoftheCell(GarlandScience2008),65,Figure22-55MolecularBiologyoftheCell(GarlandScience2008),66,Figure22-56MolecularBiologyoftheCell(GarlandScience2008),67,Figure22-57MolecularBiologyoftheCell(GarlandScience2008),68,Figure22-57aMolecularBiologyoftheCell(GarlandScience2008),69,Figure22-57bMolecularBiologyoftheCell(GarlandScience2008),70,Figure22-58MolecularBiologyoftheCell(GarlandScience2008),71,Figure22-59MolecularBiologyoftheCell(GarlandScience2008),72,Figure22-60aMolecularBiologyoftheCell(GarlandScience2008),73,Figure22-60bMolecularBiologyoftheCell(GarlandScience2008),74,Figure22-61MolecularBiologyoftheCell(GarlandScience2008),75,Figure22-62MolecularBiologyoftheCell(GarlandScience2008),76,Figure22-63MolecularBiologyoftheCell(GarlandScience2008),77,Figure22-64aMolecularBiologyoftheCell(GarlandScience2008),78,Figure22-64bMolecularBiologyoftheCell(GarlandScience2008),79,Figure22-65MolecularBiologyoftheCell(GarlandScience2008),80,Figure22-66MolecularBiologyoftheCell(GarlandScience2008),81,Figure22-66aMolecularBiologyoftheCell(GarlandScience2008),82,Figure22-66bMolecularBiologyoftheCell(GarlandScience2008),83,84,15-4.CELLMOVEMENTSANDTHESHAPINGOFTHEVERTEBRATEBODY,85,TheXenopusegganditsasymmetries.(A)Sideviewofaneggphotographedjustbeforefertilization.,86,ThePolarityoftheAmphibianEmbryoDependsonthePolarityoftheEgg,Theasymmetricdistributionofmoleculesinsidetheegg,andhowthischangesfollowingfertilizationsoastodefineadorsoventralaswellasananimalvegetalasymmetry.Fertilization,throughareorganizationofthemicrotubulecytoskeleton,triggersarotationoftheeggcortex(alayerafewmmdeep)throughabout30relativetothecoreoftheegginadirectiondeterminedbythesiteofspermentry.Somecomponentsarecarriedstillfurthertothefuturedorsalsidebyactivetransportalongmicrotubules.TheresultingdorsalconcentrationofWnt11mRNAleadstodorsalproductionoftheWnt11signalproteinanddefinesthedorsoventralpolarityofthefutureembryo.,Figure22-69MolecularBiologyoftheCell(GarlandScience2008),87,ThestagesofcleavageinXenopus.Thecleavagedivisionsrapidlysubdividetheeggintomanysmallercells.Allthecellsdividesynchronouslyforthefirst12cleavages,butthedivisionsareasymmetric,sothatthelower,vegetalcells,encumberedwithyolk,arefewerandlarger.,88,Theoriginsofthethreegermlayerscanbetracedbacktodistinctblastomeresoftheembryoinitsearlycleavagestages.Theendodermderivesfromthemostvegetalblastomeres,theectodermfromthemostanimal,andthemesodermfromamiddlesetthatcontributealsotoendodermandectoderm.Thecoloringineachpictureisthemoreintense,thehighertheproportionofcellprogenythatwillcontributetothegivengermlayer.,89,Theblastula.Intheoutermostregionsoftheembryo,tightjunctionsbetweentheblastomeresbegintocreateanepithelialsheetthatisolatestheinterioroftheembryofromtheexternalmedium.Na+ispumpedacrossthissheetintothespacesintheinterioroftheembryo,andwaterfollowsintothesespacesbecauseoftheresultingosmoticpressuregradient.Asaresult,theintercellularcrevicesinsidetheembryoenlargetoformasinglecavity,theblastocoel(囊胚腔).InXenopusthewalloftheblastocoelisseveralcellsthick,andonlytheoutermostcellsaretightlyboundtogetherasanepithelium.,GastrulationTransformsaHollowBallofCellsintoaThree-LayeredStructurewithaPrimitiveGut,90,Acrosssectionthroughthetrunkofanamphibianembryoaftertheendofgastrulation,showingthearrangementofendodermal,mesodermalandectodermaltissues.Theendodermwillformtheepithelialliningofthegut,andmanyassociatedglands.Thesalivaryglands,theliver,thepancreas,thetrachea,andthelungs.Theendodermformsonlytheepithelialcomponentsofthesestructurestheliningofthegutandthesecretorycellsofthepancreas,forexample.Themesodermgivesrisetotheconnectivetissuesatfirsttotheloose,space-filling,three-dimensionalmeshofcellsintheembryoknownasmesenchyme,andultimatelytocartilage,bone,andfibroustissue,includingthedermis(theinnerlayeroftheskin).Themesodermalsoformsthemuscles,theentirevascularsystemincludingtheheart,thebloodvessels,andthebloodcellsandthetubules,ducts,andsupportingtissuesofthekidneysandgonads.Theectodermwillformtheandepidermalappendages.Itwillalsogiverisetothewholeofthenervoussystem,thesensorycellsofthenose,theear,theeye,andothersenseorgans.,91,92,Sortingout.Cellsfromdifferentpartsofanearlyamphibianembryowillsortoutaccordingtotheirorigins.Intheclassicalexperimentshownhere,mesodermcells(green),neuralplatecells(blue),andepidermalcells(red)havebeendisaggregatedandthenreaggregatedinarandommixture.Theysortoutintoanarrangementreminiscentofanormalembryo,witha“neuraltube”internally,epidermisexternally,andmesoderminbetween.,93,NeuraltubeformationinXenopus,94,Thebendingofanepitheliumthroughcellshapechangesmediatedbymicrotubulesandactinfilaments.Thediagramisbasedonobservationsofneurulationinnewtsandsalamanders,wheretheepitheliumisonlyonecelllayerthick.Astheapicalendsofthecellsbecomenarrower,theiruppersurfacemembranebecomespuckered.,95,15-5.THEMOUSE,Theearlystagesofmousedevelopment.Thezonapellucidaisajellycapsulefromwhichtheembryoescapesafterafewdays,allowingittoimplantinthewalloftheuterus.,96,Scanningelectronmicrographsoftheearlymouseembryo,97,Aprocedureforcreatingachimericmouse.Twomorulaeofdifferentgenotypesarecombined.,98,MakingachimericmousewithEScells.TheculturedEScellscancombinewiththecellsofanormalblastocysttoformahealthychimericmouse,andcancontributetoanyofitstissues,includingthegermline.ThustheEScellsaretotipotent.,99,Branchingmorphogenesisofthelung.(A)HowFGF10andSonichedgehogarethoughttoinducethegrowthandbranchingofthebudsofthebronchialtree.Manyothersignalmolecules,suchasBMP4,arealsoexpressedinthissystem,andthesuggestedbranchingmechanismisonlyoneofseveralpossibilities.,InteractionsBetweenanEpitheliumandMesenchymeGenerateBranchingTubularStructures,100,Acastoftheadulthumanbronchialtree,preparedbyinjectingresinintotheairways;resinsofdifferentcolorshavebeeninjectedintodifferentbranchesofthetree.,101,15-6.NEURALDEVELOPMENT,102,Thecentralchallengeofneuraldevelopmentistoexplainhowtheaxonsanddendritesgrowout,findtheirrightpartners,andsynapsewiththemselectivelytocreateafunctionalnetwork,Thecomplexorganizationofnervecellconnections.,103,Thethreephasesofneuraldevelopment.,104,Diagramofa2-daychickembryo,showingtheoriginsofthenervoussystem