Changes in Synthesis of RNA and Protein During Reactivation of Delayed Implanting Mouse Blastocysts

Abstract

A series of experiments are reviewed that deal with various aspects of RNA and protein synthesis during the developmental diapause and reactivation associated with delayed implantation of mouse embryos. Results of these experiments demonstrate that rates of synthesis of RNA and protein are reduced during the quiescent period associated with delayed implantation and increase with reactivation of the embryos. The level of overall synthesis of RNA was found to increase slowly but steadily over a 24 hr period, reflecting primarily an increase in the rate of synthesis of ribosomal RNA, while there appeared to be a marked but transient burst in synthesis of mRNA within the first 3–4 hr. This increase in synthesis of mRNA was found to be linked temporally to an a-amanitin sensitive increase in protein synthesis. In addition, there appeared to be an even earlier increase in protein synthesis that was insensitive to a-amanitin. These results suggest that the overall mechanism responsible for the embryonic diapause and reactivation of delayed implanting mouse embryos has both transcriptional and translational components. It is speculated that the primary response to the maternal signal is at the level of translation of existing mRNA and that the remainder of the metabolic changes and the subsequent developmental arrest are a consequence of a reduction in necessary proteins. Further experimental approaches to test this hypothesis are suggested.