Activation of embryonic genes during preimplantation rat development

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Abstract
Expression of the embryonic genome has been examined during preimplantation rat development. Proteins synthesized at different stages of embryogenesis were labelled with [35S]methionine and then separated by one‐dimensional gel electrophoresis. A major transformation in the pattern of protein synthesis has been observed between the two‐ and the four‐cell stages of embryonic development. Also the culture of embryos with an inhibitor of transcription (α‐amanitin) has shown that the first α‐amanitin‐sensitive events take place during the late two‐cell stage. However, inhibition of transcription does not arrest the embryo development up to the four‐cell stage. Taken together, the results indicate that in rats the initiation of embryonic gene activation occurs at the late two‐cell stage. However, the first two cleavage divisions can occur in the absence of transcription.