OOCYTE DEVELOPMENT AND INCORPORATION OF H³- THYMIDINE AND H³-URIDINE IN PECTINARIA (CISTENIDES) GOULDII

¹ Department of Biology, University of Notre Dame, Notre Dame, Indiana 46556, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. The development and growth of the primary oocytes in the coelomic fluid are described. Oocytes progress from a packet stage to a single oocyte stage accompanied by vegetative growth of the germinal vesicle. Evidence presented indicates that the germinal vesicle breaks down and the oocyte reaches the first maturation division prior to shedding under natural conditions.

2. Nuclear uptake of H³-thymidine is confined to the ovarian cells following the last oogonial division in the premeiotic phase. There is evidence that free coelomic oocyte packets incorporate H³-thymidine directly into the cytoplasm. The cytoplasmic label is removed by treatment with DNase.

3. Short pulses of H³-uridine are taken up diffusely by the ovarian oocytes while small packets and single oocytes incorporate H³-uridine primarily in the nucleus and in the nucleolus. Extended exposure from 4 to 48 hours indicates that some of the nuclear uridine moves into the cytoplasm in the packet oocytes. Individual oocytes show strong nuclear labeling up to 72 hours after injection. Particularly long exposures of 6 days indicate that the uridine accumulates in the cytoplasm in the largest oocytes.

4. Treatment with RNase removes most of the nuclear and cytoplasmic H³- uridine label. Some of the nuclear label is resistant and is not removed by RNase or DNase.