Biochemical Consequences of Ethidium Bromide Treatment of Sea Urchin Embryos

Abstract

ETHIDIUM bromide (EB) forms complexes with DNA by intercalation between adjacent bases¹ and this property makes it a useful agent for developmental studies. Some effects of EB on amphibian and echinoderm development and on regeneration in Acetabularia have already been described². We have also reported that EB, at relatively high concentrations (50–100 µg/ml.) and short exposure intervals, stops the prophase condensation of the chromatin of sea urchin eggs and inhibits amino-acid incorporation and DNA synthesis³. These observations led to a more-detailed biochemical study of the effects of EB on developing sea urchin embryos. We now report that continuous exposure to low concentrations of EB (15 µg/ml.), which blocks the development of sea urchin embryos at the beginning of gastrulation², reduces the incorporation of amino-acids into acid insoluble material during the formation of the blastula and almost completely inhibits the synthesis of ribosomal RNA; no formation of poly-ribosomes can be demonstrated in treated embryos.