Effect of 5-bromodeoxyuridine on the size distribution of DNAs isolated from sea urchin embryos

Abstract

5-BROMODEOXYURIDINE (BUdR), an analogue of thymidine, has been shown to selectively inhibit cell differentiation in various cell types and development of embryos, without affecting cell maintenance capabilities¹. Gontcharoff and Mazia² demonstrated that exposure of newly fertilised sea urchin eggs or early cleavage stage embryos to BUdR resulted in embryos which did not gastrulate or produce echinochrome pigment. From this laboratory evidence has been reported³ for a BUdR-induced modification of DNA replication in developing sea urchin embyros. Pulse-chase experiments in sea urchin gastrulae demonstrated that newly synthesised low molecular weight (8-15S) nuclear DNA labelled with ³H-BUdR was not readily chased by unlabelled BUdR into higher molecular weight DNA. In contrast, 8-15S DNA labelled with ³H-thymidine was converted into higher molecular weight DNA during a relatively short chase period with unlabelled thymidine. This data suggested the incorporation of BUdR into newly synthesised low molecular weight DNA molecules in embryos might prevent or slow the rate of normal linkage of such molecules into higher molecular weight DNA.