POLY(A)+ RNA-METABOLISM DURING OOGENESIS IN XENOPUS-LAEVIS

In this study, we have measured the synthesis and turnover of oligo(dT)cellulose-bound RNA [poly(A)+ RNA] in Xenopus laevis oocytes at the maximal lampbrush chromosome stage (stage 3) and at the completion of oocyte growth (stage 6). Oocytes at both stages are shown to be active in the synthesis of poly(A)+ RNA. In stage 6 oocytes, the mean rate of synthesis of stable poly(A)+ RNA is 15% the instantaneous rate of synthesis, while the mean half-life of the unstable component is 1.6 hr. In contrast, the instantaneous rate of synthesis in stage 3 oocytes is about one-third that seen in stage 6, and most of it is devoted to the production of unstable species with an average half-life of 5 hr. Studies on the nuclear versus the cytoplasmic distribution of the newly synthesized poly(A)+ RNA demonstrated that by the end of a 12-hr labeling period for stage 3 oocytes and a 24-hr labeling period for stage 6 oocytes, approximately half of the material was cytoplasmic. This cytoplasmic material had the same electrophoretic mobility as bulk poly(A)+ RNA. Similarly, as with bulk poly(A)+ RNA, little, if any, of the newly synthesized material was found to be polysomal. Also, poly(A) labeling studies indicated that the newly synthesized poly(A)+ RNA was associated with the synthesis of poly(A) of the same length as that appearing on bulk poly(A)+ RNA. Studies on the content of bulk oligo(dT)cellulose-bound RNA indicated that about 86 ng is present in both stage 3 and stage 6 oocytes. The continual synthesis of poly(A)+ RNA throughout oogenesis in the absence of its accumulation led to the conclusion that it must be turning over. These data are discussed in relation to the hypothesis that bulk levels of poly(A)+ RNA are maintained by continually changing rates of synthesis and degradation. © 1979.