DNA synthesis turned on in unfertilized sea urchin eggs by treatment with NH 4OH

Abstract

DNA synthesis is initiated in unfertilized sea urchin eggs ( Strongylocentrotus purpuratus and Lytechinus pictus) by exposing them to NH 4OH-sea water (ordinary sea water titrated to pH 9–9.1 with NH 4OH). The eggs are considered to be unfertilized eggs by visual and electro-biological criteria and because they can later be fertilized and then do give visible and electrobiological fertilization reactions. The incorporation of 3H-thymidine proceeds in rounds, the magnitude increasing in successive rounds. It is also reported that the treatment with NH 4OH activates the uptake of thymidine by the eggs, although the internal thymidine builds up more slowly in unfertilized eggs treated with NH 4OH than it does in fertilized eggs. The magnitude of the incorporation of exogenously supplied labelled thymidine into DNA is lower in the NH 4OH-treated unfertilized eggs than in normal fertilized eggs. This difference is not attributed to differences in the amount of DNA synthesized and the explanation is sought in thymidine uptake and nucleotide pathways.