This proposal is a continuation of ongoing studies on the regulation of expression of mRNAs during mouse oocyte maturation and early embryogenesis, and the role of small RNAs. mRNAs for actin and HPRT are known to undergo opposite transitions during meiotic maturation: actin mRNA is deadenylated and its translation greatly decreased; HPRT mRNA undergoes adenylation and its translation is activated. By injecting hybrid or truncated mRNAs into mouse oocytes and following their fate, we will attempt to determine the sequences within the mRNAs that signal their respective deadenylation or adenylation. Several lines of evidence suggest an important role for a long (>30A's) poly(A) tail in promoting translation in this system. Translation of injected mRNAs with and without a long poly(A) tail will be compared in full-grown oocytes or eggs. We will also inject such RNAs into growing oocytes to determine the signal for storage or translation at the time of synthesis. We will test the effect of injected poly(A) , and we will compare the length of the poly(A) tails on translated and nontranslated poly(A)+ molecules in full-grown oocytes. A survey for the presence of mRNAs coding for growth factors or cell cycle proteins detectable on Northern blots will be carried out; for those mRNAs showing translational control, experiments to locate sequence specific signals will be undertaken. The second major aspect of this proposal deals with the role of small RNAs. We will attempt to determine whether small B2 RNAs, which are usually abundant in eggs and early embryos, play a role in translation. We have found that they are associated with polysomes in full-grown oocytes, but in eggs or in somatic tissue. The association will be explored further, and the effect of injecting antisense B2 RNAs into growing or full-grown oocytes on translation and on maturation assessed. A survey of small B1 RNAs and of total poly(A)+ RNAs will be carried out.
