NUCLEIC ACID SYNTHESIS IN PREIMPLANTATION RABBIT EMBRYOS .1. QUANTITATIVE ASPECTS, RELATIONSHIP TO EARLY MORPHOGENESIS AND PROTEIN SYNTHESIS

The ability of rabbit embryos to incorporate tritiated uridine and thymidine into acid‐insoluble material in vitro has been quantitated by liquid scintillation counting at daily intervals throughout the preimplantation period. The ribonucleic acid content of the embryos has been determined by the orcinol reaction. It is shown that, in spite of a low level of Actinomycin D‐sensitive uridine incorporation during cleavage, there is no net synthesis of ribonucleic acid until immediately prior to blastocyst formation. The acceleration of ribonucleic acid synthesis which occurs at that time precedes, by some 36 hours, the acceleration of protein synthesis. This finding is discussed from the standpoint of genetic expression in the preimplantation rabbit embryo, and with reference to the possibilities for post‐transcriptional control of protein synthesis. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company