Regulation of Polypeptide Synthesis During Early Embryogenesis of Ilyanassa obsoleta

Abstract

We have shown by two-dimensional electrophoresis of in vivo labeled polypeptides that stage-specific changes in polypeptide synthesis occurred during the early embryogenesis of the Ilyanassa embryo, and that more than 98% of the 350 polypeptides synthesized during this time were translated from maternal mRNAs. The removal of the polar lobe had no effect on polypeptide synthesis during early cleavage, but by the mesentoblast-stage there had occurred in the lobeless embryo a change in the rate of accumulation of 11 polypeptides, all of which were translated from maternal mRNAs. We have found no unequivocal evidence for the differential localization of mRNAs in the polar lobe. Our observations on polypeptide synthesis in the isolated polar lobe have indicated that the cytoplasm of the polar lobe contains both repressors of translation and activators of mRNPs. In embryos treated with actinomycin D we have observed an increased rate of accumulation of 14 polypeptides at the mesentoblast-stage of development. We have interpreted this as an example of ‘superinduction’ that resulted from transcriptionally dependent events repressed by actinomycin D. We have postulated that this actinomycin D-sensitivity indicates the transcription of regulatory genes. These genes produce translational repressors that decrease the rate of translation of these 14 polypeptides in the normal embryo. Because the synthesis of six of these polypeptides is also increased by removing the polar lobe, we suggest that the transcription of the regulatory genes controlling the translation of these six peptides is induced by the polar lobe cytoplasm.