GeneRegulationandDevelopment：基因调控和发育.ppt

GeneRegulationandDevelopment MakingoftheComplexLivingthings Inthedevelopmentofmulticellorganisms asingle cellzygotegivesrisetomanydifferentcelltypes Eachtypehasdifferentstructure undertakingdifferentchemicalandbiologicreactionsandperformscorrespondingfunctions Alltheseeventsarecontrolledbysetsofgenesinthecellandinfluencedbysurroundingstimuli BodysystemofmulticellorganismsCellsofsimilartypesareorganizedintotissuesTissueswithassociatedfunctionintoorgansOrgansofassociatedfunctionintoorgansystemsOrgansystemscoordinatelytosupportthewholeorganismProcessofembryonicdevelopmentmustgiverisenotonlytothecellsofdifferenttypesbutalsotohigher levelstructuresandcoordinatedfunctions Howlifebegin Anorganismarisesfromafertilizedeggastheresultofthreeinterrelatedprocesses celldivision celldifferentiation andcellmorphogenesis Duringdevelopment cellsbecomespolarized startsdivideunevenly reprogramsgeneexpressionandbecomespecializedinstructureandfunction aprocesscalleddifferentiation Theprocessesofmorphogenesisisformingofshapes givecells tissuesandorganstheirpropershapetofittheircorrespondingfunctions Alltheseprocessesarepartofdevelopment EmbryonicDevelopment Fertilizationresultsinazygoteandtriggersembryonicdevelopment Plasmamembrane Tail Middlepiece Neck Head Nucleus Acrosome Mitochondrion spiralshape OnlyonespermwillpenetratethishumaneggtoinitiatethefertilizationThereisaselectionofspermquality Thespermapproachestheegg 1 2 3 4 Thesperm sacrosomalenzymesdigesttheegg sjellycoat Proteinsonthespermheadbindtoeggreceptors 5 Thespermnucleusenterstheeggcytoplasm Theplasmamembranesofspermandeggfuse 6 Afertilizationenvelopeforms SPERM Nucleus Acrosome Plasmamembrane Spermhead Acrosomalenzymes Jellycoat ZonaPellucida Vitellinelayer Plasmamembrane Cytoplasm EGGCELL Receptorproteinmolecules Spermnucleus Eggnucleus 7 Thenucleiofspermandeggfuse Zygotenucleus Cleavagestarts Fertilizationofovum Oviduct Secondaryoocyte Ovulation Ovary Blastocyst implanted Endometrium Uterus Inmammals fertilizationoccursintheoviduct Spermfuseswithoocyteinmetafase2 completesmeiosisandthentwoparenteralpronucleifusetoformthediploidzygote CellDivision CleavageisthefirstmajorstepofembryonicdevelopmentItistherapidsuccessionofcelldivisionsItcreatesamulticellularembryoItpartitionsthemulticellularembryointodevelopmentalregionsCellsandembryobecomepolarizedCleavageisControlledbycyclinsandcyclin dependentkinases Cdks Duringcleavage thezygoteisdividedintosmaller smallercellscalledblastomeresEmbryovolumedoesnotchange Non differentiatedcellsandcangiverisetoanytissue Stemcellscontinuetodivideandremainundifferentiated Totipotent cellsthatcangiverisetoanycelltypesPluripotent cellsthatcangiverisetomultiplecelltypesTissue specific cangiverisetoonlyoneorfewercelltypes Blastomeres Celldivideandcellnumberincreasecontinueouslyfor5 6days 3 4daysinmice toproducethefirstmorphologicallydifferentiatedstructureThefirsttwodifferentcelltypeswithtotallydifferentgeneexpressionpatternsTheblastocystconsistsof Outerlayer Trophoblastcell whichsecretesenzymestoenabletheblastocysttoimplantonendometriumsurfaceandlaterformsplacentaInnerlayer InnerCellMass whichisundifferentiatedandageneralsourceofembryonicstemcell whichdeveloptocompletebodyparts ENDOMETRIUM Innercellmass Cavity Trophoblast Blastocyst AntibodyagainstOct4 Trophoblast Egg Sperm Blastocyst Embryo Embryonicstem cellculture Innercell mass Oncespermandeggcellfuse zygote cellstarttodivideanddifferentiate Thefirstdifferentiatedstructure ablastocyst Theinnercellmassoftheblastocystdevelopsintoembryo Embryonicstemcells EScells areisolatedfromtheinnercellmass ESCellCulture Determination Theearliestchangesthatsetacelltoaspecializedstagewithoutturningbackatmolecularlevel Canonlybe seen byexperimentCellsoccupyaspecificlocationintheembryoTheyarenot naturally totipotentanymoreMolecularchangesthatdrivestheprocessintheembryoistermeddetermination thebeginningofdifferentiation Duringembryonicdevelopment cellsbecomeobviouslydifferentinstructureandfunctionastheydifferentiate CellDifferentiation GeneexpressionisswitchedtoanewprogramCellsinitiatedevelopmentalchangesbyusingnewtranscriptionalfactorsandgiveatotallydifferentpatternofgeneexpressionCellsbecomecommittedtoaparticulardevelopmentalpathway viageneticprogramunderthedifferentialinheritanceofcytoplasmicdeterminantsviaenvironmentalcell cellinteractionsCellsare morphologically distinguishablebydifferentsizeandshape DifferentiatedCells Thesecellsproducetheproteinsthatallowthemtocarryouttheirspecializedrolesintheorganism Forexample onlylenscellsdevote80 oftheircapacityforproteinsynthesistomakingjustonetypeofproteins crystallins Theseformtransparentfibersthatallowthelenstotransmitandfocuslight Similarly skeletalmusclescellshavehighconcentrationsofproteinsspecifictomuscletissues suchasmuscle specificversionofthecontractileproteinmyosinandthestructuralproteinactin Theyalsohavemembranereceptorproteinsthatdetectsignalsfromnervecells Morphogenesis PolarCelldivisionTheorientationofthemitoticspindledeterminestheplaneofcelldivisionineukaryoticcells Ifspindleiscentrallylocated twoequal sizeddaughtercellswillresult Ifspindleisofftooneside twounequaldaughtercellswillresultCellshapeandsizeInanimals celldifferentiationisaccomplishedbyprofoundchangesincellsizeandshape Nervecellsdeveloplongprocessescalledaxons SkeletalmusclescellsarelargeandmultinucleatedCelldeath Necrosisisaccidentalcelldeathingroup notcell specific Apoptosisisprogrammedcelldeath canhappeninindividualcells Isrequiredfornormaldevelopmentinallanimals Deathprogram pathwayconsistsof Activator inhibitorandapoptoticproteaseCellmigration Cellmovementinvolvesadhesionandlossofadhesionbetweencellsandsubstrate Cell to cellinteractionsareoftenmediatedthroughcadherins Cell to substrateinteractionsofteninvolvecomplexesbetweenintegrinsandtheextracellularmatrix ECM Gastrulationproducesathree layeredembryo Thesecondmajorstepofembryonicdevelopment producesathree layeredembryoIthappensafterimplantationThesizeofembryosstartstogrowItaddsmorecellsandvolumetotheembryoItsortsallcellsintothreedistinctcelllayersTheembryoistransformedfromtheblastulaintothegastrulaThethreelayersEctoderm theouterlayerEndoderm aninnerlayer giverisetotheembryonicdigestivetractMesoderm whichpartlyfillsthespacebetweentheectodermandendoderm Embryonictissuelayersbegintodevelopintospecifictissuesandorgansystemsaftergastrulation Theembryofloatsinamnioticcavity chorionandembryonicmesodermformstheplacenta Placenta Allantois Yolksac Mother sbloodvessels Amnioticcavity Embryo Chorion Chorionicvilli Functionsofthechorion ProvidenutrientsandO2tothefetusSecretehormonesintothemothertohelpretainthefetusRepressthemother simmuneresponsetopreventrejectionofthefetusTheplacenta schorionicvilliabsorbfoodandoxygenfromthemother sblood Embryonicinductioninitiatesorganformation Inductionisthemechanismbywhichonegroupofcellsinfluencesthedevelopmentoftissuesandorgansfromectoderm endoderm andmesodermAdjacentcellsandcelllayersusechemicalsignalstoinfluencedifferentiationChemicalsignalsturnonasetofgenesinthereceivingcellsandleadstodifferentiationintoaspecifictissuesfromthesecellsPatternformationPatternformationistheemergenceofstructuresintheircorrectrelativepositionsItofteninvolvestheresponseofcellsandtheirgenestospatialgradientofchemicals Induction TissuesandorganstakeshapeinadevelopingembryoasaresultofCelldivisionCellshapechangesCellmigrationProgrammedcelldeath apoptosis Ectoderm PatternFormation Differentiationiscarefullyorchestrated ProliferationCellmigrationInteractions Induction Epithelial mesenchymaltransformationsEpithelialfolding movement evagination fusionApoptosis Apoptosis LineageanalysisofC eleganshighlightsanotheroutcomeofcellsignaling programmedcelldeathorapoptosis Thetimelysuicideofcellsoccursexactly131timesinthecourseofC elegans snormaldevelopment Atpreciselythesamepointsindevelopment signalstriggertheactivationofacascadeof suicide proteinsinthecellsdestinedtodie Ifitweren tforapoptosis youmaylookalittledifferent Apoptosispathwaysinhumansandothermammalsaremorecomplicated Researchonmammalshaverevealedaprominentroleformitochondriainapoptosis Signalsfromapoptosispathwaysorotherssomehowcausetheoutermitochondrialmembranetoleak releasingproteinsthatpromoteapoptosis Acellmustmakealife or death decision bysomehowintegratingboththe death and life growthfactor signalsthatitreceives Apoptosisisessentialtothedevelopmentofanimalmorphogenesis preventswebbingbetweenfingersandtoes ModelOrganism 1 TheWorm ThenematodeC elegansnormallylivesinthesoilbutiseasilygrowninpetridishes Onlyamillimeterlong ithasasimple transparentbodywithonlyafewcelltypesandgrowsfromzygotetomatureadultinthreeandahalfdays Itsgenomehasbeensequenced Becauseindividualsarehermaphrodites itiseasytodetectrecessivemutations Self fertilizationofheterozygoteswillproducesomehomozygousrecessiveoffspringwithmutantphenotypes AfurtherimportantfeatureisthateveryadultC eleganshaveexactly959somaticcells Thesearisefromthezygoteinvirtuallythesamewayforeveryindividual StudyingWorms C elegansisaveryusefulmodelorganismforinvestigatingtherolesofcellsignalingandinductionindevelopment Thepathwayfromfertilizedeggtoadultnematodeinvolvesfourlarvalstages thelarvaelookmuchlikesmallerversionsoftheadult duringwhichthevulvadevelops Sixcellspresentontheventralsurfaceofthesecond stagelarvagivesthevulva Asinglecellintheembryonicgonad theanchorcell initiatesacascadeofsignalsthatestablishesthefateofthevulvaprecursorcells Vulvadevelopmentinthenematodeillustratesseveralimportantdevelopmentalconcepts Inthedevelopingembryo sequentialinductionsdrivetheformationoforgans Theeffectofaninducercandependonitsconcentration Inducersproducetheireffectsviasignal transductionpathwayssimilartothoseoperatinginadultcells Theinducedcell sresponseisoftentheactivation orinactivation ofgeneswhichestablishesthepatternofgeneactivitycharacteristicofaparticularcelltype Geneticsasapowerfulapproachforelucidatingthemechanismsofdevelopment Afatemaptracesthedevelopmentofanembryo ModelOrganism 2 TheFruitFly ThefruitflyDrosophilamelanogasterwasfirstchosenasamodelorganismbygeneticistT H Morganandintensivelystudiedbygenerationsofgeneticists Thefruitflyissmallandeasilygrowninthelaboratory Ithasagenerationtimeofonlytwoweeksandproducesmanyoffspring Embryosdevelopoutsidethemother sbody Inaddition therearevastamountsofinformationonitsgenesandotheraspectsofitsbiology However becausefirstroundsofmitosisoccurswithoutcytokinesis partsofitsdevelopmentaresuperficiallyquitedifferentfromwhatisseeninotherorganisms SabotagingtheFruitFlies Inthe1940s EdwardB LewisdemonstratedthatthestudyofmutantscouldbeusedtoinvestigateDrosophiladevelopment Hestudiedbizarredevelopmentalmutationsandlocatedthemutationsonthefly sgeneticmap Thisresearchprovidedthefirstconcreteevidencethatgenessomehowdirectthedevelopmentalprocess Inthelate1970s ChristianeN sslein VolhardandEricWeischauspushedtheunderstandingofearlypatternformationtothemolecularlevel TheirgoalwastoidentifyallthegenesthataffectsegmentationinDrosophila Mutationsthataffectsegmentationarelikelytobeembryoniclethals leadingtodeathattheembryonicorlarvalstage Becauseofmaternaleffectsonaxisformationintheegg theyalsoneededtostudymaternalgenes Afterayearofhardwork theyidentified1 200 outofafruitflies13 000 genesessentialforembryonicdevelopmentAbout120ofthesewereessentialforpatternformationleadingtonormalsegmentation Theywereabletomapthesegenes Theresultsofdetailedanatomicalobservationsofdevelopmentinseveralspeciesandexperimentalmanipulationsofembryonictissueslaidthegroundworkforunderstandingthemechanismsofdevelopment Lifecycleofthefruitfly Homeotic SelectorHOXGenes Amongthemostfascinatingkindsofabnormalitiesinanimalsarethoseinwhichonenormalbodypartisreplacedbyanother WilliamBateson 1894 cataloguedseveralodditiesofthisnaturecoiningthetermhomeotictodescribethem CalvinBridges 1915 isolatedaspontaneousmutantofDrosophilainwhichpartofthehalterewastransformedintowingtissue Themutantwascalledbithorax duplicationofathoracicsegment Inthefollowingdecadesothermutationsaffectingsegmentidentitywereidentifiede g certainAntennapediamutationscausingtransformationofantennaeintolegs Background InDrosophila genescontrollingsegmentidentitywerefoundtobetranscriptionfactorsandcoinedtobehomeotic selectorgenes meaningthatthefateofagivensegmentwasselectedbytheexpressionofspecifichomeoticgenes Homeobox AllhomeoticgenesofDrosophilaincludea180 nucleotidesequencecalledthehomeobox whichspecifiesa60 amino acidhomeodomain Anidenticalorverysimilarsequenceofnucleotides oftencalledHoxgenes arefoundinmanyotheranimals includinghumans HowHomeodomainsWork Proteinswithhomeodomainsprobablyregulatedevelopmentbycoordinatingthetranscriptionofbatteriesofdevelopmentalgenes InDrosophila differentcombinationsofhomeoboxgenesareactiveindifferentpartsoftheembryoandatdifferenttimes leadingtopatternformation ActionofSignalingmoleculesParacrinefactors InducingfactorscontrollingformsofdevelopingorganMitogenregulatingcellproliferationMorphogenactinginadose dependentwaytopatternthecellfateswithinatargetfield Morphogens Productofthemother sbicoidgeneisessentialforsettinguptheanteriorendofthefly Thegene sproductsareconcentratedatthefutureanteriorend Thisisaspecificversionofageneralgradienthypothesis inwhichgradientsofmorphogensestablishanembryo saxesandotherfeatures Thebicoidproteinandothermorphogensaretranscriptionfactorsthatregulatetheactivityofsomeoftheembryo sowngenes Gradientsofthesemorphogensbringaboutregionaldifferencesintheexpressionofsegmentationgenes thegenesthatdirecttheactualformationofsegmentsaftertheembryo smajoraxesaredefined Thedirectionofhomeotictransformationsdependsonwhetherthemutationcauseslossofhomeoticgenefunctionwherethegenenormallyactsorgainoffunctionwherethegenenormallydoesnotact Ultrabithorax Ubx actsinthehalteretopromotehalteredevelopmentandrepresswingdevelopment LossoffunctionmutationsinUbxtransformthehaltereintoawing DominantmutationsthatcauseUbxtogainfunctioninthewingtransformthatstructureintoahaltere Inantenna to legtransformationsofAntennapediathemutantsreflectadominantgainofAntennapediagenefunctionintheantennae HomeoticMutations ExamplesofHomeoticMutations Normaladultfly Homeotic SelectorGenes Homeoticgeneproductsregulatedevelopmentwithinparasegmentaldomains AtthisstageeachbandofcellsalongtheA Paxisexpressauniquecombinationoftranscriptionfactorswhichcontrolsubsequentcelldevelopment Patternsofselectorgeneexpressionaredeterminedintheearlyembryoandmaintainedintotheadultfly ContinuousexpressionisrequiredtospecifystructuresalongtheA Paxis ThegenesareorderedonthechromosomeintheorderoftheirexpressionwithrespecttotheparasegmentsoftheDrosophilaembryo TwoofthebeststudiedselectorgenesareAntennapaedia Antp whichdominatesdevelopmentofthefourthparasegmentandUltrabithorax Ubx whichlargelycontrolsthesixthparasegment TranscriptionoftheAntpandUbxgenesbeginsinthethirdhourofembryogenesisindomainsdeterminedinpartbyvariousgap geneproductswithboundariessetupbythesegmentationgenes Homeoticgenesactinacellautonomousmanner acellwillbehaveaccordingtohomeoticgeneexpressionofitsownregardlessofthepatternofexpressionofitsneighboursMaintenanceofhomeoticgeneexpressionisthroughselfregulationandthePolycomb likeclassofgenes Selectorgenesspecifyepidermalstructures themusculature neuraltissueandgutalongtheA Paxis Twohomeoticselectorgeneclustersoccurintwogroupsonthesamechromosome five theAntennapediaComplex ANT C areexpressedintheheadregionwhilegenesintheBithoraxComplex BX C aremainlyexpressedinthoraxorabdominalregions Homeotic SelectorGenes EightGenesRegulatetheIdentityofWithintheAdultandEmbryo labial lab proboscipedia pb Deformed Dfd Sexcombsreduced Scr Antennapedia Antp Ultrabithorax Ubx abdominalA abd A AbdominalB Abd B HomeoticgenesencodenuclearproteinscontainingaDNA bindingmotifcalledahomeodomain Theproductsaretranscriptionfactorsthatspecifysegmentidentitybyactivatingmultiplegeneexpressionevents Thegenesareinitiallyactivatedimpreciselybytheconcentrationgradientsofgapgeneproducts e g Ubxisswitchedonbetweencertainconcentrationsofhunchbacktogiveabroadbandofexpressionnearthemiddleoftheembryo Later fushitarazuandevenskippedsharpenthelimitsofUbxexpressionwhichcomesintoregisterwiththeanteriorboundariesofspecificparasegments TheBX CandANT Cgeneshaveextensivenon codingsequences introns thatarecriticalinregulatingtheirindividualexpression Homeotic SelectorGenes Theembryoisshowninsideviewandincross section displayingtherelationshipbetweenthedorsoventralsubdivisionintofuturemajortissuetypesandtheanteroposteriorpatternoffuturesegments Aheavylineenclosestheregionthatwillformsegmentalstructures Duringgastrulationthecellsalongtheventralmidlineinvaginatetoformmesoderm whilethecellsfatedtoformthegutinvaginateneareachendoftheembryo Thus withrespecttotheirroleingutformation theoppositeendsoftheembryo althoughfarapartinspace arecloseinfunctionandinfinalfate FatemapofaDrosophilaembryoatthecellularblastodermstage ThepatternsofexpressioncomparedtothechromosomallocationsofthegenesoftheHOMcomplex Thesequenceofgenesineachofthetwosubdivisionsofthechromosomalcomplexcorrespondstothespatialsequenceinwhichthegenesareexpressed Notethatmostofthegenesareexpressedatahighlevelthroughoutoneparasegment darkcolor andatalowerlevelinsomeadjacentparasegments mediumcolor wherethepresenceofthetranscriptsisnecessaryforanormalphenotype lightcolorwhereitisnot Inregionswheretheexpressiondomainsoverlap itisusuallythemost posterior ofthelocallyactivegenesthatdeterminesthelocalphenotype Thedrawingsinthelowerpartofthefigurerepresentthegeneexpressionpatternsinembryosattheextendedgermbandstage about5hoursafterfertilization PatternsofExpression ContributionofBX Cgenes Ubx abdA andAbdB todeterminationofparasegmentidentity Thenumbersaboveeachlarvaindicatetheparasegments thosebelow thecorrespondingsegments Thecuticularpatternoflarvaeisusedtoassignanidentitytoeachparasegment PS whichisindicatedbycolor asdepictedinthewildtypeatthetop RedPSandsegmentlabelsindicateabnormalpatternsthatdonotcorrespondexactlytoanyfoundinwild typelarvae EffectsofMutationsinBithoraxComplex Expressionandlethalembryo