Appearance and persistence of maternal RNA sequences in sea urchin development

Abstract

This paper deals with the relationship between the single copy transcripts represented in mature oocytes of the sea urchin and the RNA sequences present in immature oocytes and embryos. We term the oocyte transcripts from single copy DNA the maternal single copy sequence set. A single copy [^3H]DNA fraction ([^3H]oDNA) enriched for sequences complementary to the maternal single copy sequence set was prepared and reacted with the different RNA preparations. The complexity of the mature oocyte RNA is estimated to be 37 × 10^6 nucleotides. At kinetic termination, [3H]oDNA reacted with the polysomal mRNA of 16-cell embryos to 73% of the reaction with mature oocyte RNA, indicating that 27 × 10^6 nucleotides of the maternal sequence set are present. With blastula mRNA the reaction equals about 56%, a complexity of 21 × 10^6 nucleotides; with gastrula mRNA, 53%, a complexity of 19 × 10^6 nucleotides. The relative amount of hybridization of [^3H]oDNA was 100% with cytoplasmic RNA of the 16-cell stage and became progressively less with the cytoplasmic RNAs of later stages. The total RNA of immature oocytes was found to include about 26 × 10^6 nucleotides of the maternal sequence set. Results of these experiments are discussed, and an interpretation of the pattern of utilization of structural genes during oocyte and embryo development is suggested.