CNOT6L Couples Selective Maternal Transcript Degradation to Meiotic Cell Cycle Progression in Oocyte

Meiotic resumption-coupled degradation of maternal transcripts occurs during oocyte maturation in the absence of mRNA transcription. The CCR4-NOT complex has been identified as the main eukaryotic mRNA deadenylase. In vivo functional and mechanistic information regarding its multiple subunits remains insufficient. Cnot6l, one of four genes encoding CCR4-NOT catalytic subunits, is preferentially expressed in mouse oocytes. Genetic deletion of Cnot6l impaired deadenylation and degradation of a subset of maternal mRNAs during oocyte maturation. Overtranslation of these undegraded mRNAs caused microtubule-chromosome organization defects, which led to activation of spindle assembly checkpoint and meiotic cell cycle arrest at prometaphase. Consequently, Cnot6l-/- female mice were severely subfertile. The function of CNOT6L in maturing oocytes is mediated by RNA-binding protein ZFP36L2, not maternal-zygotic transition licensing factor BTG4, which interacts with catalytic subunits CNOT7 and -8 of CCR4-NOT. Thus, recruitment of different adaptors by different catalytic subunits ensures stage-specific degradation of maternal mRNAs by CCR4-NOT. This study provides the first direct genetic evidence that CCR4-NOT-dependent and particularly CNOT6L-dependent decay of selective maternal mRNAs is a prerequisite for meiotic maturation of oocytes.