A micronucleus assay in sea urchin embryos

We have developed a micronucleus assay for use in sea urchin embryos. The embryos at the early blastula stage (about 256 cells) were exposed to genotoxic chemicals overnight until control embryos have reached the gastrula stage. Then all embryos were suspended in 1 M urea, dissociated by pipetting, and fixed with methanol:acetic acid (9:1). The preparations were air-dried and stained with acridine orange. The test chemicals (mitomycin C [MMC], vinblastine and 1-β- d-arabinofuranosylcytosine [Ara C]) induced clear micronuclei dose-dependently. The maximum frequency induced with MMC was 2–3% in Clypeaster japonicus and 1–2% in Hemicentrotus pulcherrimus.