Changes in RNA titers and polyadenylation during oogenesis and oocyte maturation in Xenopus laevis.

The titers of over 90 sequences isolated by cDNA cloning of oocyte poly(A)+RNA were examined during oogenesis in Xenopus laevis. The relative titers of most sequences in unfertilized eggs are established in pre-lamp brush oocytes and persist throughout oogenesis. We have identified several sequences whose titers decrease significantly during the growth phase of oogenesis as well as a few sequences whose titers increase slightly during this period. Among 21 sequences analyzed by RNA gel blots, all remained unchanged in titer during oocyte maturation. A significant fraction of early oocyte RNA does not bind to oligo(dT)cellulose, but by the end of oogenesis transcripts for many RNA species examined are detected exclusively in the poly(A)+RNA fraction. During oocyte maturation a slight size shift or a broadening of the hybridizing band can be seen for many sequences, indicative of poly(A) elongation or degradation.