Regulation of zygotic gene activation in mammals.

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The aim of this study is to examine the involvement of poly(A) tail elongation of maternal mRNA in the regulation of zygotic gene activation after fertilization. The experiments were conducted that the effect of 3'-deoxiadenosine (3'-dA) on gene activation in mouse 1-cell embryos. After incorporated into the embryos, 3'-dA is expected to be metabolized into 3'-dATP, which inhibits the addition of adenosine to poly(A) tail, working as a chain terminator.The inhibitory effect of 3'-dA on poly(A) tail elongation was confirmed by examining the cyclin A mRNA ; the poly(A) tail of cyclin A mRNA is elongated and its translation starts after fertilization, The results showed that 3'-dA inhibited the elongation of poly(A) tail and translation of cyclin A mRNA. Such an inhibition of translation was specific for cyclin A, since total protein synthesis estimated by [ィイD135ィエD1S] methionine incorporation into macro molecule was not changed by 3'-dA.Embryos were incubated with 3'-dA and the transcriptional activity was measured by in vitro transcription assay 14 h after fertilization. Two mM 3'-dA almost completely inhibited the transcriptional activity. 3'-dG examined as a control did not show any effect.These results suggest that poly(A) tail elongation of maternal mRNA triggers the zygotic gene activation after fertilization.