Nucleic Acid Chemistry of the Ilyanassa Embryo

A morphological study of Ilyanassa embryogenesis was made fromsections of several stages and the nucleic acid content wasmeasured throughout the course of development. The kineticsof uptake and incorporation of radioactive precursors into RNAwas determined. The RNAs synthesized at different stages ofembryogenesis were fractionated by methylated albumin kieselguhrchromatography, and the polyadenylation of RNA during developmentwas measured. From these studies it was concluded that the Ilyanassa embryo,beginning with the 4-cell stage, synthesizes dRNA, rRNA, 4SRNA, and 5S RNA throughout all stages of development. The extensivesynthesis of dRNA and the higher proportion of RNAs polyadenylatedby the pregastrula embryo was considered to be of particularsignificance. The localization of nucleic acids and nucleic acid precursorsin the polar lobe and the effect of removing the polar lobeon nucleic synthesis was reviewed. Recent work on the ultrastructure of the Ilyanassa egg was reviewedin relation to the problem of ooplasmic segregation. The discoveryof a new cytoplasmic organelle in the Ilyanassa oocyte was reviewed.