发育生物学-4th-Early-embryonic-development

DevelopmentalBiologySnapshotSummaryDifferentialgeneexpression(DGE)DGERegulationMethodsExpressionFunctionTranscriptionPost-transcriptionalTranslationPost-translationalRNA-levelProtein-levelForward-geneticsReverse-geneticsDevelopmentalBiologyFertilizationandearlyembryonicdevelopmentSection41.Germcelldevelopment2.Fertilization3.Cleavage4.GastrulationContents:Germcelldevelopment1.•Howarethegermcellsspecifiedanddetermine?•Howaretheprimordialgermcellsdifferentiatedintoeggsandsperm?Germcelldevelopment1.Gametesinallsexuallyreproducingorganismsarisefromtheprimordialgermcells(PGCs)Inmanyinstances(includingnematodes,flies,andfrogs),thePGCsarespecifiedanddeterminedautonomouslybythecytoplasmicdeterminantsintheeggthatarecomprisedofspecificproteinsandmRNAs.Thesecytoplasmicdeterminantsarecollectivelyreferredtoasthegermplasm(生殖质).PgranulesinC.elegansPolargranulesinDrosophilaGerminalgranulesinXenopus1.1.Caenorhabditiselegans1.2.Flies1.3.Frog1.4.Mouse—Originoftheprimordialgermcells(PGCs):Germcelldevelopment1.a)AnewlyfertilizedembryowithdispersedPgranules.b)Pgranulesarelocalizedtotheposteriorendofthezygote.c)Afterthefirstdivision,Pgranulesarepresentonlyinthesmaller,posteriorcell.d)AnotherunequaldivisiongivesrisetoasinglecellcontainingPgranules.e)Whenthelarvahatches,Pgranulesarelocalizedtotheprimordialgermcells.P-granulesegregationduringtheearlyembryonicdivisionsofthenematode,Caenorhabditiselegans1.1OriginofthePGCsinCaenorhabditiselegansGermcelldevelopment1.PIE-1isanuclearproteinthatexistsonlyinPcells,anditsabsenceleadstothedifferentiationofp1-p4intosomaticcells.Theeffectmaybetoinhibitgenetranscriptionactivityingermcells.Maintainthepropertiesofreproductivestemcells.1.1OriginofthePGCsinCaenorhabditiselegansPGCsRNA-bindingproteins:PGL1,PGL3,GLH1,GHL-41.2OriginofthePGCsinfliesUltravioletIrradiationandCytoplasmTransplantationPoleplasmTransplantation极质PoleplasmcontainstheproteinsandmRNAoftheposteriorgroupgenes(suchasOskar,gcl,Nanos,Tudor,Vasa,Valoisetc.).1.2OriginofthePGCsinfliesOskar,gcl,Nanos,Tudor,Vasa,Valoisetc.PoleplasmPolecellsPGCs1.3OriginofthePGCsinfrogGermplasmThegermplasmislocatedneartheplantpoleandisaspecialcytoplasmrichinRNAandprotein.Thefunctionofthemaincomponentsistoinhibittheexpressionofsomaticgenesintranscriptionandtranslationlevels.爪蟾1.4OriginofthePGCsinMouseGermcellspecificationinthemouseinvolvescell-cellinteractions.Inmice,thegermcellsformattheposteriorregionoftheepiblast,atthejunctionoftheepiblast,primitivestreak,andallantois.尿囊1.Germcelldevelopment2.Fertilization3.Cleavage4.GastrulationContents:Fertilizationistheprocesswherebythegametes(spermandegg)fusetogethertobeginthecreationofaneworganism.Thefertilizationgenerallyconsistsoffourmajorevents:1.Contactandrecognitionbetweenspermandegg.Thisensuresthatthespermandeggareofthesamespecies.2.Regulationofspermentryintotheegg.Onlyonespermnucleuscanultimatelyunitewiththeeggnucleus.Thisisusuallyaccomplishedbyallowingonlyonespermtoentertheeggandinhibitinganyothersfromentering.3.Fusionofthegeneticmaterialofspermandegg.4.Activationofeggmetabolismtostartdevelopment.Fertilization2.2.1StructureoftheGametes–HumanSperm•Almostallofthecell’scytoplasmiseliminatedduringspermmaturation,leavingonlycertainorganellesthataremodifiedforspermaticfunction.Eachspermcellconsistsofahaploidnucleus.Fertilization2.2.1StructureoftheGametes—HumanEggFertilization2.Stagesofeggmaturationatthetimeofspermentryindifferentanimalspecies.Inmostspecies,spermentryoccursbeforetheeggnucleushascompletedmeiosisThegerminalvesiclecontainthelargediploidnucleusoftheprimaryoocyte.Thepolarbodiesarenonfunctionalcellsproducedbymeiosis.Fertilization2.2.2TheprocessoffertilizationFertilization2.2.3ThecorticalreactionFertilization2.ThecorticalreactionoccursonceaspermhassuccessfullypenetratedanegginordertopreventpolyspermyOtherbarrierspreventpolyspermy2019identicaltwinsdizygotictwinsMMP1P1P2P2MMP1P1P2P2MP1MP2P1P2Chickenandzebrafincheggsrequiremultiplesperm1.Germcelldevelopment2.Fertilization3.Cleavage4.GastrulationContents:DevelopmentalBiology3CleavageCleavageCleavageisaseriesofextremelyrapidmitoticdivisionsthatimmediatelyfollowfertilization.Duringcleavage,theenormousvolumeofzygotecytoplasmisdividedintonumeroussmallercellscalledblastomeres.Concepts:ShortdivisioncycleBlastomeresizedecreasessharplyMostearlyzygotegeneareinactivatedFeatures：3CleavageMeridionalcleavage(经裂):cleavageplaneparalleltothea-vaxis.Equatorialcleavage(纬裂):cleavageplaneisperpendiculartothea-vaxis.Theorientationofcleavage:AnimalpoleVegetalpoleEquatorialcleavage3CleavageThecontentanddistributionofyolkinegg.Determinethelocationofthecleavageandthesizeoftheblastomeres,thespeedofcleavageattheanimalpole(fewyolk)isfasterthanplantpole(moreyolk).Theyolkinhibitthecleavage.Orientationofspindledeterminecleavageplane.3CleavageDeterminationofcleavageplane:Thepatternofcleavageisinfluencedbytheamountofyolkintheegg.Ineggswithlessyolk,cleavagesareequal,andtheresultingblastomeresareofsimilarsize(a).Iftheyolkislocalized,suchasinfrogeggs,thencleavagesareunequal-thecellsderivedfrom