Achromosomal Division of Early Starfish Embryos Cultured in the Presence of Actinomycin D

Abstract

Embryos of the starfish Asterina pectinifera were examined for their ability to undergo the early events of embryonic development in the presence of actinomycin D, a most widely used inhibitor of RNA synthesis. Fertilized eggs continued to divide eight or nine times in the presence of 25 p g ml-' actinomycin D, although delay of development was observed. Chromatin disintegrated in the blastomeres of actinomycin D-treated embryos specifically at the 32-cell stage and the nucleus was undetectable at later stages. Before the 32-cell stage, RNA synthesis was not affected by the presence of actinomycin D whereas DNA synthesis was severely inhibited. The stage when achrornosomal divisions cease and embryos begin to die corresponds to the period just before onset of blastulation, suggesting that the presence of the nucleus and chromosomes is a prerequisite for blastula formation and development beyond the 51 2-cell stage in this species.

Selective inhibition of gastrulation in the starfish embryo by albuside B, an inosine analogue

“…Treatments started after the onset of ciliary movement were ineffective in preventing gastrulation. It has been known that DNA replication and DNA strand separation after replication are also affected by actinomycin D [9]. We have shown previously that fertilized A. pectinifera eggs cultured in actinomycin D undergo cell division, despite an almost total absence of DNA synthesis from the 32-cell stage up to the 512-cell stage [9].…”