RNA SYNTHESIS DURING ILYANASSA OOGENESIS: AN AUTORADIOGRAPHIC STUDY

Ovarian cells of the mud snail Ilyanassa obsoleta were studied by light microscopy and autoradiography of tritiated RNA precursors. Eight stages for ovarian oocytes were devised from morphological and functional criteria. Rates of incorporation of RNA precursors were determined for seven stages by cellular compartments - cytoplasm, nucleoplasm, and nucleolus. Comparison of rates of accumulation and times of first appearance of label among the cellular compartments of the various stages gave evidence of the times, extent, and source of RNA synthesis during oogenesis. These comparisons indicate a distinct change in the nuclear pattern of RNA synthesis between stages 3 and 4; the evidence supports a predominance of ribosomal RNA synthesis in stages 1-3, with chromatin transcription increasing at stage 4 and beyond.