Quantitative changes in total RNA, total poly(A), and ribosomes in early mouse embryos☆

[摘要] ToobtaininformationontheamountsandmajorclassesofRNAstoredinthemouseeggandaccumulatedduringcleavage,wedeterminedthecontentsoftotalRNA,totalpoly(A),andribosomesfromthe1-cellstagetoblastocyst.UsingpurifiedRNAforassay,weobtainedanRNAcontentof0.35ngintheunfertilizedegg,0.24ngin2-cell,0.69ngin8-to16-cell,and1.47nginearlybastocyst(32cells).AsderivedfromEMmorphometry,thenumberofribosomesaccountsfor60–70%ofthetotalRNAcontentatallthesestages;themarkedincreaseinribosomalnumberduringcleavageisattributableentirelytonewsynthesis.Hybridizationwith[3H]poly(U)insolutionyieldedapoly(A)contentof0.7pgfortheunfertilizedeggand0.83pgforthe1-cellembryo.Thepoly(A)contentdroppedsharply,to0.26pgperembryo,bythelate2-cellstageandincreasedto0.44pgin8-to16-cellembryosand1.42pginearlyblastocysts.Hybridizationinsitugaveasimilarpatternandalsorevealedaheavylabelingofembryonucleifromthe2-cellonwardbutverylittle,ifany,labelingofthepronucleiof1-cellembryos,suggestinganabsence,orlowlevel,ofpoly(A)+RNAsynthesisatthe1-cellbutanactivesynthesisatthe2-cellandlaterstages.Thesefindingsandotheravailableevidence(e.g.,R.BachvarovaandV.DeLeon,1980,Develop.Biol.74,1–8)suggestthatthemouseembryoinheritsalargesupplyofmaternalmRNAbutthatthebulkofthisRNAiseliminatedinthe2-cellembryo.Insituhybridizationwasusedtostudytherelativeconcentrationofpoly(A)inovarianoocytes.Ingrowingoocytes,thecytoplasmicconcentrationofpoly(A)remainsaboutthesame,suggestingthattheaccumulationofpoly(A)+RNAisproportionaltooocytegrowth.Thepoly(A)contentdeclinesabouttwofoldbetweenthetimeofcompletionofoocytegrowthandfertilization.Thegerminalvesiclecontinuestobelabeleduptothetimeofovulation,raisingthepossibilitythatpoly(A)+RNAsynthesis(andpresumablyturnover)occursinfullygrownoocytes.

[学科分类] 生物科学（综合）