發(fā)育生物學(xué)體軸與胚層課件

發(fā)育生物學(xué)體軸與胚層

VertebrateembryosshowdifferencesinformbeforegastrulationAftergastrulation,rathersimilaratPhylotypicstage(種系型期):headstructure,neuraltube,notochord,somitesLifecycleofthemouse

9weeksfertilizationintheoviduct,meioisIIcompletedclevagemorula卵裂蛙的早期卵裂。A第一次卵裂，B第二次卵裂，C第四次卵裂，動物極和植物極細(xì)胞出現(xiàn)差異。卵裂期是指受精卵開始有絲分裂并產(chǎn)生由較小的細(xì)胞構(gòu)成的囊胚(blastula)的過程。主要特點包括：分裂周期短;分裂球的體積下降：海膽胚胎的質(zhì)/核比由550降至6;早期卵裂中合子基因大多處于休眠狀態(tài)；卵裂常經(jīng)歷由均等裂向不均等裂變化。3.hatching1.compaction2.blastocystcavityformationgeneexpressionstarts128cellDay7-humanDay5.5-mouse哺乳動物的早期卵裂發(fā)生在輸卵管中Mousepre-implantationstages:cleavage,compaction,blastocystcavityformationCompactionatthelate8-cellstage,Withapical-basalpolarizationofcells128-cellblastocystcompaction128-cellblastocyst

緊密化(Compaction):8細(xì)胞分裂后不久，卵裂球突然擠在一起，卵裂球之間的接觸面增大，形成一個緊密的細(xì)胞球體。哺乳動物卵裂球的compaction:發(fā)生第三次卵裂后不久小鼠8細(xì)胞胚胎compaction前后小鼠桑椹胚的壓縮現(xiàn)象8細(xì)胞時期，小鼠細(xì)胞表面光滑，微絨毛均勻分布，壓縮后微絨毛僅分布于細(xì)胞的外表面，細(xì)胞之間的聯(lián)系加強了。未壓縮的和壓縮的8細(xì)胞小鼠胚胎的比較Compaction的機制:

8細(xì)胞胚胎的外層胞間形成致密連接(tightjunctions)，可將球內(nèi)部的細(xì)胞與外環(huán)境隔絕，起穩(wěn)定細(xì)胞球的作用。而內(nèi)層胞間形成縫隙連接

(gapjunction)，可以交換小分子和離子。

注射E-Cadherin抗體的胚胎不能夠致密化。在4細(xì)胞期激活蛋白激酶C導(dǎo)致compaction發(fā)生。因此，Compaction可能始于蛋白激酶C的活化，它引起細(xì)胞骨架的重排，在膜上均勻分布的E-Cadherin重新定位在胞間相交處。哺乳動物囊胚細(xì)胞命運的早期分化－位置決定論16細(xì)胞期桑椹胚(morula):位于內(nèi)部的少數(shù)細(xì)胞產(chǎn)生的子細(xì)胞將組成內(nèi)細(xì)胞團(innercellmass)，而位于外部的細(xì)胞產(chǎn)生的子細(xì)胞大多構(gòu)成滋養(yǎng)外胚層(trophoblast)。32細(xì)胞期胚泡(blastocyst):位于囊胚腔一端的內(nèi)細(xì)胞團(約10個細(xì)胞)將發(fā)育胚胎的本體及與其相連的卵黃囊、尿囊和羊膜；外層的滋胚層生成絨毛膜，為胎兒從母體攝取營養(yǎng)物質(zhì)和氧，并產(chǎn)生激素以避免母體的排斥反應(yīng)。內(nèi)細(xì)胞團的產(chǎn)生是哺乳動物早期發(fā)育的關(guān)鍵步驟之一。通過對活體胚胎的觀察研究，發(fā)現(xiàn)這種重要決定作用僅僅依賴于細(xì)胞于某一正確時間出現(xiàn)在某一正確的位置。壓縮后位于外層的細(xì)胞將形成滋養(yǎng)層細(xì)胞，而內(nèi)部的細(xì)胞將發(fā)育成胚胎。一個細(xì)胞是否成為胚胎或滋養(yǎng)層細(xì)胞，完全取決于壓縮作用后細(xì)胞所處的位置是位于外周還是內(nèi)部。哺乳動物胚泡的著床胚泡在向子宮移動過程中體積增大，是由定位于滋胚層細(xì)胞膜囊胚腔一側(cè)的Na－K泵將外部Na+泵入腔中，最后通過滲透作用吸水使囊胚腔增大。隨著囊胚腔內(nèi)離子濃度的增加，水分就通過滲透作用進(jìn)入進(jìn)入囊胚腔內(nèi)。囊胚腔內(nèi)液體的積累對囊胚腔壁造成一個向外的壓力，這種靜水壓是參與形成和維持囊胚為球形的一個重要作用力。哺乳動物胚泡的著床胚胎外的透明帶阻止了胚泡與輸卵管壁的粘連-異位妊娠。胚泡到達(dá)子宮時，胚胎細(xì)胞分泌Strypsin（一種類胰蛋白酶)，它使透明帶穿孔，胚泡從孔中“孵化”(hatch)出與子宮壁接觸，通過一系列反應(yīng)而著床。人類的同卵雙生的發(fā)生(占出生總數(shù)的0.25%)分離發(fā)生在滋胚層形成前(約受精后5天前)的分割，有獨立的絨毛膜和羊膜。占同卵雙生的33%。發(fā)生在滋胚層形成后但羊膜形成前(約受精后5－9天)的分割，共用絨毛膜，有獨立的羊膜。占同卵雙生的66%發(fā)生在羊膜形成后(約受精9天后)的分割，共用絨毛膜和羊膜，易出現(xiàn)連體兒。人類的連體嬰兒嵌合胚：早期卵裂球有同等的發(fā)育潛力。自然人群中也出現(xiàn)過同時有XX型和XY型細(xì)胞的人，異卵雙生的兩個胚胎融合形成的單一混合個體。。胚胎干細(xì)胞：保持了分化為胚胎本體的潛能的、可在體外增殖的胚胎細(xì)胞。在基因功能研究和疾病治療方面有重要的作用。哺乳動物中的嵌合胚、胚胎干細(xì)胞人工受精：如主要用于治療不育癥、保存和運輸優(yōu)良個體。胚胎切割：在2－4細(xì)胞期分割胚胎細(xì)胞，用于繁殖優(yōu)良家畜個體。哺乳動物中的人工受精和胚胎切割原腸作用Gastrulation原腸作用是指囊胚細(xì)胞有規(guī)則的移動，使細(xì)胞重新排列，用來形成內(nèi)胚層和中胚層器官的細(xì)胞遷入胚胎內(nèi)部，而要形成外胚層的細(xì)胞鋪展在胚胎表面。原腸作用期的胚胎叫原腸胚(gastrula)。通過原腸作用，胚胎首先建立起三個胚層，即外胚層、中胚層和內(nèi)胚層；其次為重新占有新位置的胚胎細(xì)胞之間的相互作用奠定了基礎(chǔ)。因此，原腸作用是從尚未分化到分化為三個胚層和器官原基決定的關(guān)鍵時期。

動物身體的主軸（包括前后軸、背腹軸和左右軸）也會在卵裂和原腸作用期間建立起來，胚胎各部分的細(xì)胞會獲得各自的發(fā)育潛能。人類的原腸作用上胚層和下胚層的形成：在原腸作用開始時，內(nèi)細(xì)胞團分裂為兩層。與囊胚腔接觸的一層為下胚層，將用于形成yolksac；另一層為上胚層。上胚層細(xì)胞間的縫隙將合并、擴大成為羊膜腔，腔中的液體可防止胚胎脫水和保護(hù)胚胎受振蕩。上胚層將發(fā)育為胚胎的本體。原腸作用前的胚泡，示內(nèi)細(xì)胞團和滋養(yǎng)層細(xì)胞。下胚層細(xì)胞從內(nèi)細(xì)胞團中分離出來形成卵黃囊，滋養(yǎng)層細(xì)胞分裂形成細(xì)胞滋養(yǎng)層和合胞體滋養(yǎng)層；細(xì)胞滋養(yǎng)層形成絨毛，合胞體滋養(yǎng)層融入子宮組織。上胚層分裂形成羊膜外胚層（包繞羊膜腔）和胚胎上胚層，哺乳類胚胎由胚胎上胚層形成。胚外內(nèi)胚層形成卵黃囊人體胚胎三胚層的建立及其命運人類原腸作用過程中，羊膜結(jié)構(gòu)的形成和細(xì)胞的運動。Note:thehumanepiblastisaflatdisc.Themouseepiblastiscup-shaped--hardertovisualize.40天妊娠后人類的胚胎被羊膜包裹，外面再被絨毛膜包被。血管已深入到絨毛膜內(nèi)，絨毛膜上的微絨毛最大限度地與母體血液接觸。人類胚胎與母體間的物質(zhì)交流人體胚胎細(xì)胞的分化路線Earlypost-implantationdevelopmentofthemouseembryoInnercellmass:primitiveendoderm(extra-embryonicmembrane)andprimitiveectodermorepiblast(embryoproperandsomeextra-embryoniccomponents)

Polartrophectoderm:theectoplacentalconeandtheplacentaMuraltrophectoderm:trophoblastgiantcellsEarlypost-implantationdevelopmentofthemouseembryoEggcylinder:aninternalcavity(proaminoticcavity)forms,U-shaped

Onsetofgastrulation:theappearanceofprimitivestreak小鼠胚胎上胚層細(xì)胞的程序性死亡導(dǎo)致囊胚腔的形成。Gastrulationinthemouseembryo6.5d:

beginningofgastrulation,theappearanceofprimitivestreak;antero-posterioraxis

7.5d:primitivestreakelongatesuntilthebottomofthecup,formingnotochord(headprocess)Gastrulationandneurulationinthemouseembryo7d:thenodeformation,anteriorectoderm→neurectoderm(brainandspinalcord)

Theanteriorpartoftheembryogrowsinsizeandheadfoldappears,definitiveendodermreplacevisceralendodermtoformanouterlayerontheventralsurfaceoftheembryo.Thenotochordbeginstoform.Gastrulationandneurulationinthemouseembryo8d:headisdistinct,neuralfoldshaveformed,guthaveclosed,somitesbeginstoformoneithersideofthenotochord.10.5d:thecompleteofgastrulationandneurulationafterturning.TuninginthemouseembryoTurning:adevelopmentalquirkpeculiartorodents:humanembryosaresurroundedbytheirextra-embryonicmembranesfromthebeginning.8.5-9.5d:themouseembryobecomesentirelyenclosedintheprotectiveamnionandamnioticfluid.Thevisceralyolksac,amajorsourceofnutrition,surroundstheaminon,theumbilicalcordconnectstotheplacenta.胚軸形成胚胎細(xì)胞形成不同組織、器官，構(gòu)成有序空間結(jié)構(gòu)的過程稱為圖式形成（patternformation）。在動物胚胎發(fā)育中，最初的圖式形成主要涉及胚軸（embryonicaxes）形成及其一系列相關(guān)的細(xì)胞分化過程。胚軸指胚胎的前－后軸（anterior-posterioraxis）和背–腹軸（dorsal-ventralaxis）。胚軸的形成是在一系列基因的多層次、網(wǎng)絡(luò)性調(diào)控下完成的。Bodyaxesformation：小鼠胚胎發(fā)育的早期無法辨認(rèn)體軸Thespecificationoftheinnercellmassofamouseembryodependsontherelativepositionofthecellswithrespecttotheinsideandoutsideoftheembryos.Transcriptionfactors:Cdx2(滋養(yǎng)層細(xì)胞的分化)andOct/4(內(nèi)細(xì)胞團的分化)TheaxesoftheearlymouseembryoBlastocyststage:4d:innercellmassisconfinedtoembryonicregionandthisdefinesanembryonic-abembryonicaxis(geometrically,notcellfate)5.5d:theantero-posterioraxisvisible,withtheformationofprimitivestreakattheposteriorend.Thesymmetry-breakingeventisthespecificationoftheanteriorvisceralendoderm(前端內(nèi)臟內(nèi)胚層,AVE)

5.5d:

Asmallregionofvisceralendodermatthedistal-mostendofthecupisspecifiesasAVEinducedbyNodalsignalingfromtheepiblastandbeginstoproliferateandextendtoonesideofepiblast.Theanteriorfateisrestrictedtothedistalregionbyinhibitorysignalsfromtheextra-embryonicectodermtotheproximalvisceralendoderm;inducesanteriorectodermThesymmetry-breakingeventisthespecificationoftheanteriorvisceralendoderm(前端內(nèi)臟內(nèi)胚層,AVE)

6.5d:

primitivestreakbeginstoformontheoppositeside,markingtheposteriorendoftheaxisRoleoftheAVEinestablishingtheanterior-posterioraxisofthemouseembryoCylindricalSymmetryBilateralSymmetryAPCerberus(anti-Nodal)Dkk(anti-Wnt)Lefty(anti-Nodal)Otx2AnteriorneuralectodermNodal,Cripto(co-receptorForNodal)Endo-mesoderminductionDay5.25Day5.5Day6.25orhypoblastEndo-mesoderminduction,Primitivestreakwnt,brachyury,fgfexpressedEpiblastectodermTheleft-rightasymmetryWhilethevertebratebodyisoutwardlysymmetric,mostinternalorgansareinfactasymmetricwithrespecttotheleftandrightsides,calledleft-rightasymmetry,e.g.,theheart,therightlunghasmorelobesthantheleft.1/10,000inhumans,situsinversusmutationintheivgenecauses50%ofmicehaveheartsthatlooptotheright.Keyproteinsinestablishingleftness:extracellelarsignalproteinNodalandtranscriptionfactorPitx2Determinationofleft-rightasymmetryinthechickleft-rightsymmetryisbrokenatanearlystagebytheasymmetricactivityofaproton-potassiumpump(H+/K+-ATPase)ThereleaseofCa2+fromcellsintheleftsideaspartofthesymmetry-breakingprocess.Pitx2:leftness;Lefty(Nodalantagonist)providemidlinebarriertopreventNodalcrossingtotheright-handside;ActivininhibitShhactivityLeft-rightasymmetryinthemouseembryoCilia(纖毛)-directedflowgeneratesleft-rightasymmetryDirectedleftwardflowofextracellularfluidatthenodeataroundthelatehead-foldstageLeftwardflowoffluidpropagatesthereleaseofintracellularCa2+toupregulateNodalexpressionontheleftside胚層的來源和特化(specification)

Fatemap:telluswhichtissuesthedifferentregionsoftheembryogiverisetoThefatemapsandthegenesinvolvedingerm-layerspecificationaremoresimilarinallvertebratemodelsthanareinearlyaxisspecification

根據(jù)被標(biāo)記細(xì)胞的命運，構(gòu)建兩棲類早期囊胚的命運圖：labeledbyinjectionofhigh-molecular-weightmoleculessuchasrhodamine(cannotpassthroughcellmembranes),asrhodaminefluorescesredinUVlight,sodetectedunderaUVmicroscope.Thefluorescentproteingreenfluorescentprotein(GFP)isnowwidelyused.胚層的來源和特化(specification)FatemappingoftheearlyXenopusembryo:C3islabeledwithfluorescein(green)---tailbudstage,thecellsgiverisetomesodermcells胚層的來源和特化(specification)FatemapofalateXenopusblastula

Ectoderm:epidermis,nervoussystemAlongthedorso-ventralaxisthemesoderm:notochord,somites,heart,kidneyandbloodEndodermoverlyingthemesoderminthemarginalzoneFatemapofamouseatthelategastrulastageNode:exclusivelynotochordThemiddlepartofthestreak:mainlylateral-platemesodermTheposteriorpartofthestreak:tailbud,extra-embryonicmesodermthatformstheextra-embryonicmembranes-theamnion,visceralyolksac,allantois.不同脊椎動物的fatemap基于一個圖式的改變Similarities:thefuturenotochordmesodermoccupiesacentraldorsalposition;theneuralectodermliesadjacenttothenotochord,withtherestoftheectodermanteriortoit.Differences:mainlytotheyolkinessofthedifferenteggs,whichdeterminesthepatternsofcleavageandinfluencestheshapeoftheearlyembryo.EndodermoverlyingthemesoderminthemarginalzoneFatemapsofvertebrateembryosatalateblastulaorearlygastrula早期脊椎動物的胚胎細(xì)胞的命運并未決定，是可以調(diào)整的Fusionofmouseembryosgiverisetoachimera(micethataremosaicsofcellswith2differentgeneticconstitutions-byfusing2embryos):8-cellstageembryoofanunpigmentedstrainofmouseisfusedwithapigmentedstrainwillgiverisetoachimericanimalGraftingexperiments:transplantingthecellsorregionstoahostembryo,ifdetermined,theywilldevelopaccordingtotheiroriginalposition;ifnotyetdetermined,developinlinewiththenewpositionEarlymouseembryoscanregulatetoachievethecorrectsize:retainsconsiderablecapacitytoregulateuntillateingastrulation.Innercellmassremainpluripotentupto4.5daysafterfertilization-theycangiverisetomanycelltypes.CellsinICMcanbeculturedtoproduceembryonicstemcells(EScells)小鼠發(fā)育相關(guān)突變的產(chǎn)生Studyingtheroleofaparticulargeneindevelopment,tostudytheeffectsofamutationinthatgeneMice:transgenictechniques,overexpressorknock-outagivengeneIntroducingembryonicstemcells(EScells)carryingthemutationintotheblastocyst小鼠的中胚層誘導(dǎo)和模式建成發(fā)生在原條形成時期

6days:theAVEinduceanteriorcharacterintheunderlyingepiblastandearlymarkersofthefutureprimitivestreak(PS)arerestrictedtotheproximalepiblast

6.5days:

BMPactivatestheexpressionofmesodermmarkersandtheposteriormovementofcellsexpressingPSmarkersresultsinPSformation小鼠的中胚層誘導(dǎo)和模式建