第8章动物发育遗传调控

Sagiv精英名校考 ChapterTheGeneticControlofAnimalDevelopment动物发育的遗传调乔中东教授

动物发育的遗传调 Sagiv

ChapterTheprocessofDevelopmentin ysisofDevelopmentinModel ZygoticGeneActivityin ysisofDevelopmentin

动物发育的遗传调 Sagiv精英名校考研 StemCellTherapy:ABraveNew

动物发育的遗传调 Sagiv精英名校考 SectionTheProcessofDevelopmentin动物的发Celldivision,cellmovement,andcellspecializationallplayrolesintheformationofamulticellularanimalfromafertilizedegg.

动物发育的遗传调 Sag精英名校考研 /AnimaldevelopmentactuallybeginsfertilizationoftheCriticalsubstancesaresynthesizedbythefemaleandsequesteredintheeggtonourishandcontrolthedevelopmentofthezygoteintoamulticellularorganisms.Afterfertilization,arapidseriesofmitoticdivisionsincreasesthenumberofcellsinthe animals,usuallywithoutmuchgrowthinoverallsize.

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sagiv精英名校考 Theresultingmassofcells,theblastula,isrelativelynondescript,burevenatthisstage,someofitscellshavebeenearmarkedtoformspecifictissuesintheanimal’sbody.Suchcellshavebeenfated,ordetermined,todevelopinacertainway.

动物发育的遗传调 Sagiv精英名校考 Asdevelopmentcontinues,theblastulaisreorganizedbyaseriesofcellmigrations,collectivelycalledgastrulation,toproduceanembryowiththreedistinctlayers—ectoderm(ontheoutside),mesoderm(inthemiddle),andendoderm(ontheinside).Thesethreelayersgiverisetospecifictissues,whicharethenassembledtoform

动物发育的遗传调 Sagiv精英名校考 Fromgastrulationonward,cells differentfromeachother,aprocesscalledThisisakeyfeatureofanimaldevelopment,providingthemanyspecializedfunctionsthatareneededforlife.

动物发育的遗传调 Sag精英名校考研 /OogenesisandAllthedevelopmentpotentialofananimaliscontainedinafertilizedegg.Whenspermandeggunite,theybringtogetherthepaternalandmaternalsetsofgenes,whichprovidethedetailedinstructionsfordevelopment.However,developmentisalsoprofoundlyaffectedbycytoplasmicmaterialspresentintheegg.

动物发育的遗传调 Sag精英名校考研 /Someofthesematerials,suchasyolk,arenutritiveandserveasfoodforthe Othermaterialsaredeterminativeinthattheyhelptoplayoutthebasicpatternofdevelopmentitself.Boththenutritiveanddeterminativecomponentsoftheeggcytoplasmaremanufacturedduringoogenesis,theprocessofeggformation.

动物发育的遗传调 Sagiv精英名校考 Thisinvolvesacomplexseriesofevents,includingthetwomeioticdivisions,whichreducethechromosomesnumberfromdiploidtohaploid.Curiously,thesecondmeioticdivisionissometimesnotcompleteduntilaftertheegghasbeenfertilized.

动物发育的遗传调 Sagiv精英名校考 Infemaleanimals,themeioticdivisionsproducecellsofunequalsize.Thefirstdivisionseparatesalargecell,thesecondaryoocyte,fromasmallcell,thefirstpolarbody.Thesecondaryoocytegoesontodevelopintotheegg,whereasthepolarbodyThisunequaldivisionofcellsisclearlyawayofmusteringmaterialsintotheegg

动物发育的遗传调 Sag精英名校考研 /Thesecondmeioticdivisionisalsounequalinthatmostofthecytoplasmis theegg;onlyatinybitispinchedofftoformthesecondpolarbody.Neighboringcellsalsoenrichthecytoplasmoftheegg.Inmanyorganisms,thesecellssynthesizematerialsthataretransportedintotheoocyte,performinganourishingornursing

动物发育的遗传调 Sag精英名校考研 /Surroundingcellsmayalsoprovidematerialstoenveloptheoocyte.Inbirds,forexample,ahard,calcium-rich isformedbysecretionsintheoviduct,apartofthefemalereproductivetractthroughwhichtheeggpassesinitswayoutofthebody.

动物发育的遗传调 Sagiv精英名校考 Fertilizationoccurswhenaneggispenetratedbyasperm.Thisisacomplexprocess,involvinginteractionsbetweendifferentproteinsinthesurfacesofthetwogametes.Whenthespermmakescontactwiththeegg,ittriggersaresponseintheeggthatcausesthecytoplasmnearthesurfaceoftheeggtoenvelopthespermandinternalizeit.

动物发育的遗传调 Sagiv精英名校考 Afterthespermhasenteredtheegg,theeggcompletesmeiosis(ifithasnotalreadydoneso)andthespermandeggnucleifusetoformthenucleusofthezygote.Insomeorganisms,forexample,Drosophila,thespermandeggnucleiactuallydivideoncemitoticallybeforefusing.

动物发育的遗传调 Sag精英名校考研 /TheEmbryonicDivisionsandBlastulaAnewlyformedzygotequicklydividesintotwocells,eachofwhichdividesintotwomore,andsoon,untilmanycellsarepresentinthedevelo Theseinitialdivisionsarecalledcleavage Sometimestheyoccurasymmetricallysothatthedaughtercellsreceivedifferentamountsofcytoplasm.

动物发育的遗传调 Sagiv精英名校考 ScanningelectronmicrographofanembryoofthemarinesnailIIyanassaobsoletaattheeight-cellstage.Thethincellinthecenterisapolar

动物发育的遗传调 Sagiv精英名校考 However,exceptforafewcuriouscases,eachcellseemstogetthesamegeneticThus,theirsubsequentdifferentiationintospecificcelltypesisnotduetothesegregationofgenesorchromosomes,butrathertotheactivationorrepressionofspecificsetsofgenes.

动物发育的遗传调 Sagiv精英名校考 Thedifferentiationofcelltypesisprecededbydetermination,aprocessinwhichcellsintheblastulaareassigneddevelopmentalThishasbeenconfirmedbyexperimentsinwhichapieceoftheblastulaissurgicallyexcisedandmovedtoadifferentposition,oreventoadifferentorganism.Insomecases,thesetransplantssurviveanddifferentiatejustastheywouldhaveiftheyhadnotbeenmoved.

动物发育的遗传调 Sagiv精英名校考 Thus,evenbeforethereisanyvisibleevidenceofspecialization,someofthecellsintheblastulaaredeterminedtodevelopinaspecificway.Bythetimeofblastulaformation,thebasicdevelopmentalplanoftheanimalhasalreadybeenlaiddown.

动物发育的遗传调 Sagiv精英名校考 GastrulationandThecellsoftheblastulaarereorganizedbygastrulation,aseriesofmovementsinwhichgroupsofcellsmigratetonewpositionsintheembryo.Thisconvertsthenondescriptblastula,whichisessentiallyasphereofcells,intoanorganismwithdistinctcelllayers,oftencalledtheprimarygermlayer原胚层，notbeconfusedwiththegermcells).

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sag精英名校考研 /Theselayersformoftheprimitivetissuestheanimal—ectoderm,mesoderm,andendoderm—andeventuallydifferentiateintospecifictissues—nerve,epithelium,muscle,blood,bone,hair,gland,viscera,andsoforth.Itisthereforethroughacombinationofcellmovementanddifferentiationthatthebodyofananimaltakesshape.Inthecourseofthisprocess,oftencalledmorphogenesis,individualorganssuchasbrain,heart,intestine,andliverareformed

动物发育的遗传调 Sagiv

KeyThedevelopmentofamulticellularanimalinvolvestheassignmentoffatestocells(determination)andthesubsequentrealizationofthosefates(differentiation).Keymaterialsfortheearlyphasesofanimaldevelopmentaretransferredintotheeggduringoogenesis.

动物发育的遗传调 Sagiv

KeyAfterfertilization,theeggproceedsthroughseveralcleavagedivisionstoformasphereofcells(theblastula),whichissubsequentlyreorganizedbycellmovementstoformtheprimarygermlayers(ectoderm,mesoderm,andendoderm).Duringmorphogenesis,tissuesandorgansareformedfromtheprimarygerm

动物发育的遗传调 Sag精英名校考研 /Section ysisofDevelopmental发育途径的遗传Developmentalpathwayscanbestudiedbyidentifyinggeneswhoseproductsareinvolvedinthedifferentiationofspecific

动物发育的遗传调 Sagiv精英名校考 Thenotionthatphenotypesresultfromaseriesofstepsinapathwayandthatgenescontroleachofthesestepsemergedinthe1930sand1940sfromacombinationofgeneticandbiochemicalinvestigations.Bythattime,ithadalreadybeenestablishedthatcellscarryoutamultitudeofbiochemicalreactions,eachcatalyzedbyanenzyme,andthatseveralreactionscanbelinkedtoformapathway.

动物发育的遗传调 Sagiv精英名校考 Geneticsprovidedthekeyinsightthateachenzymeinapathwayisencodedbyagene.Amutationinoneofthesegenescouldthereforeinactivateanessentialenzyme,blockingtheentirepathwayandcausingamutantphenotype.Geneticistsquicklyrealizedthatbystudyingsuchmutations,theycouldidentifyeachstepinthepathway.

动物发育的遗传调 Sag精英名校考研 /Furthermore,by yzingpairsofmutations,theycouldsometimesarrangethestepsinthecorrecttemporalorder.Thisgeneticdissectionofbiochemicalpathwayswassoonextendedtootherbiologicalprocesses,includingdevelopment.

动物发育的遗传调 Sagiv精英名校考 Adevelopmentalpathwayconsistsoftheeventsinvolvedinthedifferentiationoftissuesandorgans.Differentgeneproductsparticipateintheseevents,includingsomethataresignalmolecules,somethataresignalreceptors,othersthataresignaltransducers,andstillothersthataretranscriptionfactors.Otherkindsofregulatoryproteinsmayalsobeinvolved.

动物发育的遗传调 Sag精英名校考研 / y,apathwaygeneratesthecomponentsthatformthestructuresofparticulartissuesandorgans.ItthereforecreatesaThecomponentsofapathwayarecausallyorderedbythewayinwhichtheybringaboutthephenotype.GeneAmayproduceasecretedproteinthatactsasasignaltostimulatethetranscriptionofgeneX,whoseproductisacomponentofadifferentiatedcell.

动物发育的遗传调 Sagiv精英名校考 Thisstimulationmaybemediatedbyothergeneproducts,including,forexample,amembrane-boundreceptorfortheAprotein,intracellularproteinsthatareactivatedbythisreceptor,andoneormoretranscriptionfactorsthatrespondtothisactivationbybindingtoenhancersneargeneXtoinduceitsexpression.

动物发育的遗传调 Sag精英名校考研 /Inthisdevelopmentalpathway,thedifferentproteinsareorderedbyacausalchainthat yproducesaproteincharacteristicofaparticulardifferentiatedcell.

动物发育的遗传调 Sag精英名校考研 /InDrosophilaandCaenorhabditis,thedevelopmentalpathwaysforsexualdifferentiationhavebeenamongthemostthoroughlystudied.ThesepathwayscontrolthedifferentiationofthesomatictissuesintomaleorfemaleOther,lesswellunderstood,ernthedevelopmentofthetissuesinthemaleandfemalegermline.

动物发育的遗传调 Sagiv精英名校考 TheDrosophilaandCaenorhabditissomaticsex-determinationpathwaysinvolveentirelydifferentmolecularmechanisms.InDrosophila,thekeygenesencodeproteinsthatregulateRNAsplicing,whereasinCaenorhabditis,theyencodesignalingmolecules,theirreceptors,andtranscription

动物发育的遗传调 Sagiv精英名校考 Inbothanimals,however,thesex-determinationpathwayrespondstothesamefundamentalsignal,whichistheratioofXchromosomestoautosomes.Whenthisratiois1.0orgreater,thepathwayproducesafemalephenotype(orahermaphroditephenotypeinC.elegans),whereaswhenitis0.5orlessitproducesamalephenotype.

动物发育的遗传调 Sagiv精英名校考 SexdeterminationinThesex-determinationpathwayinDrosophilahasthreecomponents:⑴asystemtoascertaintheX:Aratioveryearlyintheembryo;⑵asystemtoconvertthisratiointoadevelopmentalsignal;and⑶systemtorespondtothissignalbyproducingeithermaleorfemalestructures.

动物发育的遗传调 Sag精英名校考研 /SexAscertainingtheX:AThesystemtoascertaintheX:Aratioinvolvesinteractionsbetweenmaternallysynthesizedproteinsthathavebeendepositedintheeggcytoplasm,andembryonicallysynthesizedproteinsthatareencodedbyseveralX-linkedgenes.

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sagiv精英名校考 Becauseofstrictdose-dependencetheselatterproteinsaretwiceasabundantinXXembryosasinXYembryos,andthereforeprovideameansof“counting”thenumberofXchromosomespresent.BecausethegenesthatencodetheseproteinsaffecttheX:Aratio,theyarecallednumeratorelements.

动物发育的遗传调 Sagiv精英名校考 OthergeneslocatedontheautosomesaffectthedenominatoroftheX:Aratio.Theseso-calleddenominatorelementsencodeproteinsthatantagonizetheproductsofthenumeratorelements.Consequently,asthedosageofdenominatorelementsisincreased,the“perceived”dosageofnumeratorelementsisdecreased,andthenumberofXchromosomespresentinthegenotypeisunderestimated.

动物发育的遗传调 Sagiv精英名校考 ThisprocessoccursinDrosophilawithtwoXchromosomesandthreepairsofautosomes(genotypeXX;AAA);suchfliesdevelopasintersexesratherthanasfemales.ThesystemforascertainingtheX:AratioinDrosophilaisthereforebasedinantagonismbetweenX-linked(numerator)andautosomal(denominator)geneproducts.

动物发育的遗传调 Sagiv精英名校考 GeneratingaDevelopmentalOncetheX:Aratiohasbeenascertained,itisconvertedintoamolecularsignalthatcontrolstheexpressionoftheX-linkedSex-lethal(Sxl)gene,themasterregulatorofthesex-determinationpathway.Earlyindevelopment,thissignalactivatestranscriptionoftheSxlgenefromPE,thegene’s“early”promoter,butonlyinXX

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sagiv精英名校考 TheearlytranscriptsfromthispromoterareprocessedandtranslatedtoproducefunctionalSex-lethalprotein,denotedSXL.Afteronlyafewdivisioncycles,transcriptionfromthePEpromoterisreplacedbytranscriptionfromanotherpromoter,PM,theso-calledmaintenancepromoteroftheSxlgene.Curiously,transcriptionfromthePMpromoterisalsoinitiatedinXYembryos.

动物发育的遗传调 Sag精英名校考研 /However,thetranscriptsfromPMarecorrectlyprocessedonlyifSXLproteinisConsequently,inXYembryos,wherethisproteinhasnotyetbeenmade,theSxltranscriptsarealterna ysplicedtoincludeanexonwithastopcodon,andwhenthese ysplicedtranscriptsinXYembryosdoesnotleadtotheproductionoffunctionalSXLprotein,andintheabsenceofthisprotein,theseembryosdevelopasmales.

动物发育的遗传调 Sagiv精英名校考 InXXembryos,whereSXLproteinwasinitiallymadeinresponsetotheX:Asignal,SxltranscriptionfromthePMpromoteraresplicedtoproducemoreSXLprotein.ThisexpressionpatternismaintainedbecausetheSXLproteinregulatesthesplicingoftranscriptsfromSxlgeneinsuchawaythattheyencodethefull-lengthSXL

动物发育的遗传调 Sagiv精英名校考 InXXembryos,thisproteinisthereforeapositiveregulatorofitsownsynthesis—acuriousfeedbackmechanismthatmaintainstheexpressionoftheSXLproteininXXembryosandpreventsitsexpressioninXY

动物发育的遗传调 Sagiv精英名校考 TheSXLproteinalsoregulatesthesplicingoftranscriptsfromanothergeneinthesex-determinationpathway,transformer(tra).Thesetranscriptscanbeprocessedintwodifferentways.Inchromosomalmales,wheretheSXLproteinisabsent,thesplicingapparatusalwaysleavesastopcodoninthesecondexonofthetraRNA.

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sagiv精英名校考 Thus,whensplicedtraRNAistranslated,itgeneratesatruncated(andnonfunctional)Infemales,wheretheSXLproteinispresent,theprematurestopcodonisremovedbyalternatesplicinginatleastsomeofthetranscripts.

动物发育的遗传调 Sagiv精英名校考 Thus,whentheyaretranslated,somefunctionaltransformerprotein(denotedTRA)isproduced.TheSXLproteinthereforeallowsthesynthesisoffunctionalTRAproteininXXembryosbutnotinXYembryos.

动物发育的遗传调 Sagiv精英名校考 DifferentiationinResponsetoTheTRAproteinalsoturnsouttobearegulatorofRNAprocessing.AlongwithTRA2,aproteinencodedbytransformer2(tra2)gene,itcontrolstheexpressionofdoublesex(des),anautosomalgenethatcanproducetwodifferentproteinsthroughalternatesplicingofitsRNA.

动物发育的遗传调 Sagiv精英名校考 InXXembryos,wheretheTRAproteinispresent,dsxtranscriptsareprocessedtoencodeaDSXproteinthatrepressesthegenesrequiredformaledevelopment.Therefore,suchembryosdevelopintoInXYembryos,wheretheTRAproteinisabsent,dsxtranscriptsareprocessedtoencodeaDSXproteinthatrepressesthegenesrequiredforfemaledevelopment.

动物发育的遗传调 Sagiv精英名校考 Consequently,suchembryosdevelopintoTheTRAandTRA2proteinsalsocontroltheprocessingoftranscriptsfromanotherautosomalgenecalledfruitless(fru).

动物发育的遗传调 Sagiv精英名校考 MutationsintheSex-MutationshavebeenobtainedineachofthegenesoftheDrosophilasex-determinationLoss-of-functionmutationsinSxlpreventSXLproteinfrombeingmadeinHomozygousmutantswouldthereforedevelopintomales;however,theydieas

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sag精英名校考研 /Thisembryonicdeathisnotduetoincipientsexualtransformationbutrathertoanabnormalityinthedosagecompensationsystem.Inadditiontoregulatingthesex-determinationpathway,Sxlalsoregulatesdosagecompensation.Althoughthemechanismisnotfullyunderstood,itapparentlypreventsthehyperactivationofX-linkedgenesinXX

动物发育的遗传调 Sagiv精英名校考 Whenthishyperactivationoccurs,asitdoesinhomozygousSxlmutants,XXembryosdiebecausethereistoomuchX-linkedgeneHowever,inXYanimals,loss-of-functionmutationsintheSxlgenehavenoeffect,whichisconsistentwiththefactthattheSXLproteinisnormallynotmadeinmales.

动物发育的遗传调 Sagiv精英名校考 Loss-of-functionsintransformerandtransformer2havethesamephenotype:bothXXandXYanimalsdevelopintomales.ThesexualtransformationinXXanimalsdemonstratesthatboththetra+andtra2+genesareneededforfemaledevelopment.Loss-of-functionmutationsinthedsxgenecausebothXXandXYembryostodevelopintointersexes.

动物发育的遗传调 Sagiv精英名校考 Theintersexualphenotypeappearsbecauseboththemaleandthefemaledevelopmentalpathwaysareactivatedindsxmutants.

动物发育的遗传调 Sagiv精英名校考 3.SexDeterminationinThesomaticsex-determinationpathwayinCaenorhabditisinvolvesatleast10differentAsinDrosophila,mutationsinthesegenesaltersexualdevelopment.

动物发育的遗传调 Sagiv精英名校考 Forexample,loss-of-functionmutationsinthetwotransformergenestra-1andtra-2(nottobeconfusedwiththetraandtra2inDrosophila)causeXXanimalstodevelopintomales,andloss-of-functionmutationsinthehermaphroditegeneher-1causeXOanimalstodevelopintohermaphrodites.

动物发育的遗传调 Sagiv精英名校考 Thesephenotypicalternationsshowthatthetra-1andtra-2geneproductsareneededfornormalhermaphroditedevelopmentandthattheher-1geneproductisneededfornormalmaledevelopment.Loss-of-functionmutationsinthreeothergenes,fem-1,fem-2,andfem-3(forfeminization)causeXOanimalstodevelopintospermlessfemales.

动物发育的遗传调 Sagiv精英名校考 Thisfeminizedphenotypeshowsthatthefemgeneproductsareneededfornormalmaledevelopment.Researchershavebeenabletoarrangethesesixgenesinadevelopmentalpathway.Thefirstgene,her-1,encodesasecretedproteinthatislikelytobeasignaling

动物发育的遗传调 Sagiv精英名校考 Thenextgene,tra-2,encodesamembrane-boundprotein,whichmayfunctionasareceptorfortheher-1signalingprotein.Theproductsofthefemgenesarecytoplasmicproteinsthatmaytransducetheher-1signal,andlastgeneinthepathway,tra-1,apparentlyencodesazinc-finger-typetranscriptionfactor,whichmayregulatethegenesinvolvedinsexualdifferentiation.

动物发育的遗传调 Sagiv精英名校考 InCaenorhabditis,thesex-determinationpathwayseemstoinvolveaseriesofnegativeregulatorsofgeneexpression.InXOanimals,thesecretedher-1geneproductapparentlyinteractswiththetra-2geneproduct,causingit eThisinteractionallowsthethreefemgeneproductstobeactivatedandtheycollectivelyinactivatethetra-1geneproduct,whichisapositiveregulatoroffemale

动物发育的遗传调 i:74352a/hermaphroditewithoutactivetra-1protein,itdevelopsasamale.InXXanimals,theher-1proteinisnotmade;thus,itsputativereceptor,thetra-2protein,remainsactive.Activetra-2proteincausesthefemgeneproductstobeinactived,whichinturnallowsthetra-1proteintostimulatefemaleTheanimalthereforedevelopsasa

动物发育的遗传调 Sagiv精英名校考 SexualdevelopmentinCaenorhabditisfundamentallydependsontheX:Aratio,justasitdoesinDrosophila.SomehowthisratioisconvertedintoamolecularsignalthatcontrolsthesexualThissamesignalalsocontrolsthephenomenonofdosagecompensation,whichinCaenorhabditisinvolveshypoactivationofthetwoXchromosomes.

动物发育的遗传调 Sag精英名校考研 /

动物发育的遗传调 Sagiv精英名校考 ThesignalfromtheX:Aratioisfunneledintothesex-determinationand pensationpathwaysthroughapathwayinvolvingatleastfourOneofthese,xol-1,isrequiredinmalesbutnotinhermaphrodites.Loss-of-functionmutationsinxol-1cause

动物发育的遗传调 Sagiv精英名校考 Threeothergenes,sdc-1,sdc-2,andsdc-3(forsexdeterminationanddosagecompensation),arenegativelyregulatedbyLoss-of-functionmutationsinthesegeneseitherkillXXanimalsorturnthemintoThus,thesdcgenesareneededinhermaphroditesbutnotin

动物发育的遗传调 Sagiv

KeyInDrosophilathepathwaythatcontrolssexualdifferentiationinvolvessomegenesthatascertaintheX:Aratio,somethatconvertthisratiointoadevelopmentalsignal,andothersthatrespondtothesignalbyproducingeithermaleorfemale

动物发育的遗传调 Sagiv精英名校考 KeyThesex-lethal(sxl)geneplaysakeyroleinDrosophilasexualdevelopmentbyregulatingthesplicingofitsowntranscriptandthatofanothergene(tra).InC.elegans,thesexual-differentiationpathwayinvolvesgenesthatencodesignalingproteins,theirreceptors,signaltransducers,andtranscriptionfactors.

动物发育的遗传调 Sag精英名校考研 /SectionMaternalGeneActivityinDevelopment发育过程中母 的活Materialstransportedintotheeggduringoogenesisplayamajorroleinembryonicdevelopment 生成过程中转运 的物质在胚胎发育过程中发挥主要的作用

动物发育的遗传调 Sagiv精英名校考 ImportanteventsoccurinanimaldevelopmentevenbeforeaneggisfertilizedSagiv精英名校考 之前Atthistime,nutritiveanddeterminativematerialsaretransportedintotheeggfromsurroundingcells,layingupfoodstoresandorganizingtheeggforitssubsequentdevelopment—themolecularequivalentofamother’slove(在这个时候，营养物质和决定性的物质从周围细胞被转运 中，

动物发育的遗传调 Sag精英名校考研 /Thesematerialsaregeneratedbytheexpressionofgenesinthefemalereproductivesystem,somebeingexpressedinsomaticreproductivetissuesandothersonlyingerm-linetissues这些物质是在雌性生殖系统中表达产生的，有些是在体细Collectively,thesegeneshelptoformeggsthatcandevelopintoembryosafterfertilization(集中起来，这些 后能够发育成胚胎

动物发育的遗传调 Sag精英名校考研 /Insomespecies,thesematernalgeneproductslayoutthebasicbodyplanoftheembryo,distinguishingheadfromtailandbackfrombelly(有些物种中，这些母系基Thesematernally dmaterialsthereforeestablishamolecularcoordinatesystemtoguideanembryo’sdevelopment(因此这些母系提供的物质建立了协调系统以引导胚胎发育

动物发育的遗传调 Sag精英名校考研 /Mutationsingenesthatcontributetotheformationofhealthyeggsmayhavenoeffectontheviabilityorappearanceofthefemalemakingthoseeggs(对形成健康有贡献 发生突变可能对制造这些子的雌性的生存能力和外观不会发生影响Instead,theireffectsmaybeseenonlyinthenextgeneration(它们可能仅对下一代产生

动物发育的遗传调 Sag精英名校考研 /Suchmutationsarecalledmaternal-effectmutationsbecausethemutantphenotypeintheoffspringiscausedbyamutantgenotypeinitsmother这样的突变因引起的后代表型突变是由母亲的型突变引

动物发育的遗传调 Sag精英名校考研 /calledmaternal-effectgenes(通过这样的突 Thedorsal(dl)geneinDrosophilaisagood 就是个好例子Matingsbetweenflieshomozygousforrecessivemutationsinthisgeneproduceinviableprogeny(这个 子交配产生不能生存的后代Thislethaleffectisstrictlymaternal这个致

动物发育的遗传调 Sag精英名校考研 /Thematernaleffectofamutationinthedorsal(dl)geneofThemutantphenotypeisanembryothatlacksventraltissues;thatis,itisdorsalized.

动物发育的遗传调 Sag精英名校考研 /Acrossbetweenhomozygousmutantfemalesandhomozygouswild-typemalesproducesinviableprogeny,butthereciprocalcross(互交，homozygousmutantmaleshomozygoustypefemalesproducesviableprogeny但是正反ThelethaleffectofthedorsalmutationisthereforemanifestedonlyiffemalesarehomozygousforitThemalegenotypeisirrelevant(雄性

动物发育的遗传调 Sag精英名校考研 /Molecularcharacterizationofthedorsalgenehasrevealedthebasisforthismaternaleffect(Dorsal 种母系效应的基础Thedorsalgeneencodesatranscriptionfactorthatisproducedduringoogenesisandstoreintheegg(在 编码一个转录因子， 在子中

动物发育的遗传调 Sag精英名校考研 /factorplaysanimportantroleinthedifferentiationofthedorsalandventral子在胚胎的腹部和背部的分化过程中要的作用Whenitismissing,theventralpartsincorrectlydifferentiateasiftheywereonthedorsalside,creatinganembryowithtwo

动物发育的遗传调 Sag精英名校考研 /Thislethalconditioncannotbepreventedbyawild-typedorsalalleleinheritedfromthefatherbecausedorsalisnottranscribed遗传来的野生型的dorsal等 防止，为dorsal在胚胎的时候不转录Rather,becauseitsexpressionislimitedtothefemalegermline,mutationsindorsalarestrictmaternal-effectlethals在一定程统，dorsal的突变就是严格的母系效应致死

动物发育的遗传调 Sagiv精英名校考 DeterminationoftheDorsal-VentralandSagiv精英名校考 Animalswithbilateralsymmetryhavetwoprimarybodyaxes,onedistinguishingbackfrombelly(dorsalfromventral)andtheotherdistinguishingheadfromtail(anteriorfromposterior)具有两侧对称的动物都要两

动物发育的遗传调 Sag精英名校考研 /Bothoftheseaxesareestablishedveryearlyindevelopment,insomespeciesevenbefore就建立了,在一些物种中甚至在 InDrosophila,theprocessesofaxisformationhavebeendissectedgeneticallybycollectingmutationsthataffectearlyembryonicdevelopment果蝇中，轴形成的

动物发育的遗传调 Sagiv精英名校考 Inthe1970sand1980s,massiveresearchesforsuchmutationswerecarriedoutbyChristianeNüsslein-Volhard,EricWeischaus,TrudiSchüpbach,GerdJurgens,andothers.TheseresearchersusedchemicalmutagenstoinducemutationsineachoftheDrosophilachromosomes.

动物发育的遗传调 Sag精英名校考研 /Manymutationswereidentified,includingmaternal-effectlethalsingenessuchas Molecularandgenetic ysesofthesemutationshaveprovidedconsiderableinsightintotheeventsofearlyDrosophila

动物发育的遗传调 Sag精英名校考研 /FormationoftheDorsal-VentralInDrosophiladifferentiationoftheembryoalongthedorsal-ventralaxishingesontheactionofthetranscriptionfactorencodedbythedorsalgene(果蝇沿着腹背轴的胚胎分化取决于dorsal编码的转录因子的作Thisproteinissynthesizedmaternallyandstoredinthecytoplasmoftheegg(这个蛋白

动物发育的遗传调 Sagiv精英名校考 Determinationofthedorsal-ventralSagiv精英名校考 Thegenestwist,snail,zerknüllt,anddecapentaplegicareregulatedbydorsal

动物发育的遗传调 Sag精英名校考研 /Atthetimeofblastodermformation,thedorsalproteinentersthenucleiontheventralsideoftheembryo,includingthetranscriptionoftwogenescalledtwistandsnail(在胚盘形成的时候，dorsal蛋白进入 Inthesesamenuclei,itrepressesthegeneszerknüllt(fromGermanforCrumpled)anddecapentaplegic(fromGreekwordsfor15andstroke)(在同一个核内，它抑制

动物发育的遗传调 Sag精英名校考研 /Theselectiveinductionandrepressionofgenescausetheventralcellstodifferentiateintoembryonicmesoderm(选择性的诱导和抑制腹侧细胞分化进入胚胎的中胚Ontheoppositesideoftheembryo,wherethedorsalproteinisexcludedfrothenuclei,twist,snailarenotinducedandzerknülltanddecapentaplegicarenotrepressed在胚胎相对的一侧，dorsal蛋白从核中和snail不被诱导,zerknüllt和decapentaplegic

动物发育的遗传调 Sagiv精英名校考 Consequently,thesecelldifferentiateintoTheentranceofthedorsaltranscriptionfactorintotheventralnucleianditsexclusionfromthedorsalnucleithereforeinitiatedifferentiationalongthedorsal-

动物发育的遗传调 Sag精英名校考研 /Butwhattriggersthedorsalproteintomoveintothenucleiononlyonesideofthe侧核内的扳机呢Theanswerisaninteractionbetweentwoproteinsontheventralsurfaceofthe

动物发育的遗传调 Sag精英名校考研 /Oneprotein,theproductoftheTollgene(fromGermanwordfor“tuft”簇),isdistributeduniformlyovertheembryo’ssurface;thisproteinisembeddedintheplasmamembranethatsurroundstheembryo(一个蛋白是Toll 一地分布在胚胎的表面；这个蛋白植绕着胚胎浆膜中

动物发育的遗传调 Sag精英名校考研 /腹背轴分spätzle蛋白的相互作用.

动物发育的遗传

Sag精英名校考研 /Theotherprotein,theproductofthespätzlegene(fromtheGermanwordforlittledumpling)foundintheperivi linespace,a betweentheplasmamembraneandtheexternalvi membrane(另一个蛋白是 的产它在卵黄周腔隙可以被发现，浆膜和卵黄外层之间的充满液体的腔隙

动物发育的遗传

Sag精英名校考研 /Throughtheactionofaproteaseencodedbyagenecalledeaster(becauseitwasdiscoveredonEasterSunday),thespätzleproteiniscleavedtoproduceapolypeptidethatin