A comparison of the rates of accumulation of nonpolyadenylated and polyadenylated RNA in normal and delayed implanting mouse embryos

Abstract

Two experiments were done to examine changes in the rates of accumulation of RNA by mouse blastocysts entering and leaving the metabolically quiescent phase associated with delayed implantation. In both cases, normal embryos were labeled with [ 14C]uridine while delayed implanting embryos were labeled with [ 3H]uridine. The differentially labeled blastocysts were mixed together and their RNA was extracted. The overall rates of accumulation of both rRNA and mRNA were determined in delayed implanting embryos and expressed as percentages of normal. In the first experiment, delay of implantation was caused by removing the maternal ovaries at noon on the fourth day of pregnancy. The rates of accumulation of both rRNA and mRNA were found to decrease steadily over the subsequent 3–12 hr as the blastocysts entered the metabolically quiescent phase. In the second experiment, dormant embryos were reactivated by injecting ovariectomized females with estradiol. A slow but steady increase was observed in the rate of accumulation of rRNA in the following 18–21 hr; by contrast, a sharp increase was found in the accumulation of mRNA within the first 3 hr. Interestingly, this early burst was transient and subsequently the rate of accumulation of mRNA increased only slowly along with rRNA. Although the significance of the rapid increase in accumulation of mRNA during reactivation was not determined, it seems likely that it is involved with the regulation of metabolism and is part of the mechanism responsible for controlling embryonic diapause.