A study of the effects of ethidium bromide on the ultrastructure of sea urchin embryos

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Abstract
This study describes the ultrastructural changes which result from treatment of sea urchin embryos (Paracentrotus lividus) with ethidium bromide, particularly in: the chromatin (formation of a network of materials of various densities or clumping), the nucleoli (no typical granular region), the mitochondria (swelling, reduction in the number of cristae, appearance of numerous dense granules or a dense mass in the matrix) and the heavy bodies (enlargement and prolonged existence).The experimental conditions were as follows: Treatment with different doses from ten minutes before fertilization continued for 90 minutes afterwards. Treatment with a high dose (100 μg/ml) for three hours at the young blastula stage. Treatment with a low dose (15 μg/ml) for 48 hours from fertilization onwards. Active nucleo‐cytoplasmic exchange visibly occurs across the nuclear membrane of control embryos throughout development: emission of multivesicular ergastoplasmic sacs into the cytoplasm up to the blastula stage and formation of ergastoplasmic diverticulae by its outer leaflet from the gastrula stage onwards. These signs of nuclear membrane activity are also observed in embryos treated with ethidium bromide.