The CCR4-NOT complex suppresses untimely translational activation of maternal mRNAs.

Control of mRNA poly(A) tails is essential for regulation of mRNA metabolism, specifically translation efficiency and mRNA stability. Gene expression in maturing oocytes relies largely on post-transcriptional regulation, as genes are transcriptionally silent during oocyte maturation. The CCR4-NOT complex is a major mammalian deadenylase, which regulates poly(A) tails of maternal mRNAs; however, the function of the CCR4-NOT complex in translational regulation has not been well understood. Here we show that this complex suppresses translational activity of maternal mRNAs during oocyte maturation. Oocytes that lack all CCR4-NOT deadenylase activity due to genetic deletion of its catalytic subunits, Cnot7 and Cnot8, showed a large-scale gene expression change caused by increased translational activity during oocyte maturation. Developmental arrest during meiosis I in these oocytes results in sterility of oocyte-specific Cnot7- and Cnot8-knockout female mice. We further showed that recruitment of CCR4-NOT to maternal mRNAs is mediated by the 3'UTR element, CPE, which suppresses translational activation of maternal mRNAs. We propose that suppression of untimely translational activation of maternal mRNAs via deadenylation by CCR4-NOT is essential for proper oocyte maturation.