Nucleic Acid Chemistry of theIlyanassaEmbryo

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Abstract
A morphological study of Ilyanassa embryogenesis was made from sections of several stages and the nucleic acid content was measured throughout the course of development. The kinetics of uptake and incorporation of radioactive precursors into RNA was determined. The RNAs synthesized at different stages of embryogenesis were fractionated by methylated albumin kieselguhr chromatography, and the polyadenylation of RNA during development was measured. From these studies it was concluded that the Ilyanassa embryo, beginning with the 4-cell stage, synthesizes dRNA, rRNA, 4S RNA, and 5S RNA throughout all stages of development. The extensive synthesis of dRNA and the higher proportion of RNAs polyadenylated by the pregastrula embryo was considered to be of particular significance. The localization of nucleic acids and nucleic acid precursors in the polar lobe and the effect of removing the polar lobe on nucleic synthesis was reviewed. Recent work on the ultrastructure of the Ilyanassa egg was reviewed in relation to the problem of ooplasmic segregation. The discovery of a new cytoplasmic organelle in the Ilyanassa oocyte was reviewed.

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