Role of protein synthesis in the development of a transcriptionally permissive state in one-cell stage mouse embryos.

The time of onset of gene transcription in the mouse embryo is temporally regulated. A prominent feature of this regulation is a change during the one-cell stage from a transcriptionally nonpermissive state to a transcriptionally permissive state. During the early one-cell stage, the cytoplasm is either inadequate or suppressive for nuclear gene transcription, but by the late one-cell stage, the cytoplasm acquires the ability to support gene transcription either in endogenous nuclei or exogenous nuclei introduced microsurgically. We have investigated the role of protein synthesis in this cytoplasmic transition. Nuclei from two-cell stage embryos treated with alpha-amanitin were used to evaluate the transcriptional permissiveness of late one-cell stage cytoplasm, as indicated by the production of transcripts from four genes that are specifically transcribed at elevated rates during the two-cell stage. Two of these genes were transcribed following nuclear transfer to late one-cell stage cytoplasm, and two were not transcribed. Treatment of the recipient cytoplasm with cycloheximide to inhibit protein synthesis from the early to the late one-cell stage inhibited the transcription of the two genes that were transcribed in the untreated, late one-cell stage recipients. These results indicate that acquisition of the transcriptionally permissive state during the one-cell stage is facilitated by protein synthesis, and that the transcriptional permissiveness in the late one-cell stage cytoplasm is limited to certain genes.