RNA complexity in developing sea urchin oocytes

Nuclear and cytoplasmic RNAs extracted from previtellogenic and vitellogenic oocytes of the sea urchin Strongylocentrotus purpuratus were characterized by hybridization reactions with radioactively labeled single-copy sea urchin DNA. The complexity of nuclear RNA from previtellogenic oocytes was 1.6 × 10^8 nucleotides. The previtellogenic nuclear RNA sequence set is included in the hnRNA of gastrula stage embryos. The nulcear RNA of vitellogenic oocytes may also contain a class of more prevalent transcripts. A single-copy [^3H]DNA tracer enriched for the sequences of mature egg RNA was reacted with cytoplasmic RNA of previtellogenic oocytes. This experiment showed that less than half of the mature egg RNA sequence set is accumulated before the onset of vitellogenesis. Therefore, a large fraction of the maternal message sequences appears in the egg during the last several weeks of oocyte development