The CNOT4 Subunit of the CCR4‐NOT Complex is Involved in mRNA Degradation, Efficient DNA Damage Repair, and XY Chromosome Crossover during Male Germ Cell Meiosis

The CCR4‐NOT complex is a major mRNA deadenylase in eukaryotes, comprising the catalytic subunits CNOT6/6L and CNOT7/8, as well as CNOT4, a regulatory subunit with previously undetermined functions. These subunits have been hypothesized to play synergistic biochemical functions during development. Cnot7 knockout male mice have been reported to be infertile. In this study, viable Cnot6/6l double knockout mice are constructed, and the males are fertile. These results indicate that CNOT7 has CNOT6/6L‐independent functions in vivo. It is also demonstrated that CNOT4 is required for post‐implantation embryo development and meiosis progression during spermatogenesis. Conditional knockout of Cnot4 in male germ cells leads to defective DNA damage repair and homologous crossover between X and Y chromosomes. CNOT4 functions as a previously unrecognized mRNA adaptor of CCR4‐NOT by targeting mRNAs to CNOT7 for deadenylation of poly(A) tails, thereby mediating the degradation of a subset of transcripts from the zygotene to pachytene stage. The mRNA removal promoted by the CNOT4‐regulated CCR4‐NOT complex during the zygotene‐to‐pachytene transition is crucial for the appropriate expression of genes involved in the subsequent events of spermatogenesis, normal DNA double‐strand break repair during meiosis, efficient crossover between X and Y chromosomes, and ultimately, male fertility.