UTILIZATION OF ³H-THYMIDINE TRIPHOSPHATE BY DEVELOPING STAGES OF PECTINARIA GOULDII

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

1. Exposure of developing Pectinaria embryos to ³H-TTP results in immediate nuclear label over all postfertilization stages.

2. Intense nuclear label also occurs over preoocytes or oogonia within the ovary after in vivo ³H-TTP pulsing.

3. No nuclear uptake is obtained in either the packet or solitary vegetative oocyte with either ³H-TTP or ³H-TdR until after fertilization. There was no detection of mitochondrial DNA synthesis in oocytes but cytoplasmic labeling of a gregarine protozoan occurred in vivo with ³H-TTP.

4. The addition of complementary nucleosides or nucleotides has no effect on the quantitative uptake of either radioactive precursor into oocytes or developing embryos.

5. These experiments suggest that ³H-TTP is being utilized by dividing cells of Pectinaria embryos. Actual incorporation of ³H-TTP rather than degradation of TTP to TdR was implied from observations showing that no reduction of nuclear ³H-TTP occurred in the presence of excess unlabeled thymidine.