Patterns of maternal messenger RNA accumulation and adenylation during oogenesis in Urechis caupo.

We have investigated the accumulation and adenylation of the maternal mRNA during oogenesis in the oocytes of the marine worm Urechis caupo. The analysis, using in vitro translation and cDNA probes to assay for specific mRNAs, demonstrates that different maternal mRNAs accumulate with different patterns during oogenesis. One class of maternal mRNAs accumulates throughout oogenesis and remains at a steady level in the full-grown oocyte. These mRNAs do not have a poly(A) tail long enough to mediate binding to oligo(dT)-cellulose in oocytes, but are rapidly adenylated immediately following fertilization. The other maternal mRNAs accumulate in growing oocytes as poly(A)+ RNA and undergo some deadenylation in full-grown oocytes and embryos. Some of these mRNAs attain their highest concentration fairly early in oogenesis, while others continue to accumulate during later stages. Many of the mRNAs that accumulate as poly(A)+ RNA in growing oocytes diminish dramatically in concentration in full-grown oocytes.