Development of Fertilized Starfish Eggs in Which Cytokinesis is Prevented by Iturin A–2

Abstract

Iturin A-2, a cyclic peptide obtained from cultures of Bacillus subtilis inhibited cell division but not nuclear divisions of fertilized eggs of the starfish Asterina pectinifera, resulting in the formation of non-cleaving eggs containing all the embryonic nuclei in a common cytoplasm. Fertilized eggs in which cleavage was prevented by iturin A-2 (50 .mu.g/ml) synthesized DNA, RNA and the protein at comparable rates to those of normal embryos up to the onset of blastulation. In single-cell embryos, however, elevation of the level of transcription, which is a characteristic marker of blastulation, did not take place and the chromatin masses eventually dispersed in the cytoplasm. Treatment of oocytes with iturin A-2 (50 .mu.g/ml) resulted in loss of their response to the maturation-inducing substance 1-methyladenine, whose receptors are located in the cell membrane or other components of the oocyte cortex. Furthermore, iturin A-2 bound to oocyte cortices quantitatively, suggesting that its site of action is the cortices of oocytes and eggs, and that its arrest of cleavage of fertilized eggs is due to loss of the ability of the cell membrane to form a cleavage furrow.