RNA-and protein-synthesizing capacity of isolated oocytes of the sea urchin Lytechinus pictus.

Abstract Uridine- 14 C and valine- 14 C incorporation into macromolecules by suspensions of eggs of Lytechinus pictus containing varying proportions of oocytes were measured by scintillation counting and were localized within the cells by autoradiography. Mature eggs incorporated almost no uridine- 14 C while oocytes incorporated appreciable amounts. Valine- 14 C incorporation by suspensions of mature eggs in 9 experiments, ranged from 1.91 μμmoles to 3.39 μμmoles, and averaged 2.37 μμmoles per 10 4 eggs in 15 minutes. The corresponding values obtained in 10 experiments with suspensions containing various amounts of oocytes ranged from 6.12 μμmoles to 97.8 μμmoles and averaged 37.9 μμmoles, namely, approximately 16 times that of the mature eggs. Dactinomycin significantly inhibited uridine- 14 C incorporation but did not suppress valine- 14 C incorporation by the mature eggs or the oocytes. In four of the experiments (one with a mature egg suspension) dactinomycin stimulated valine- 14 C incorporation by three- to fourfold but in 10 others (two with mature egg suspensions) there was no significant difference from the control. Additional evidence that the incorporation of valine- 14 C represents synthesis rather than exchange or absorptive processes was provided by a demonstration that it takes place on polyribosomes. Autoradiographs confirmed that the mature eggs did not incorporate uridine- 14 C and incorporated only slight quantities of valine- 14 C, even in the mixed suspensions with oocytes. The oocytes incorporated uridine- 14 C primarily in the nucleolus, and this was prevented by dactinomycin. Valine- 14 C was incorporated, by the oocytes, principally in the cytoplasm and nucleolus. In sea urchins then, the oocytes appear to undergo a considerable amount of intrinsic protein and RNA synthesis. This is in contrast to the situation in many other organisms in which the oocyte apparently obtains much material from other tissues.