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 and comprise CNOT6/6L and CNOT7/8, both of which are two types of catalytic subunits, as well as CNOT4, which is a regulatory subunit with previously undetermined functions. These subunits are previously hypothesized to play synergistic biochemical functions; however, their in vivo functions have remained poorly investigated. In this study, we constructed viable Cnot6/6l double knockout mice and the males were fertile, whereas Cnot7–/– male mice have been reported to be infertile. These results are against canonical viewpoints and indicate that CNOT7 has CNOT6/6L-independent functions in vivo. We also demonstrate that the mouse testis has an endogenous complex that contains CNOT7 and CNOT4, but not CNOT6/6L. CNOT4 is required for post-implantation embryo development and meiosis progression during spermatogenesis. Selective knockout of Cnot4 in male germ cells leads to defective DNA damage repair and homologous crossover formation between X and Y chromosomes in a cell autonomous manner. CNOT4 functions as a previously unrecognized mRNA adaptor of CCR4-NOT by targeting mRNAs to CNOT7 for deadenylation of the poly(A) tails, thereby mediating the degradation of a subset of transcripts from the zygotene to pachytene stage. Therefore, the mRNA removal promoted by CNOT4-regulated CCR4-NOT complex during the zygotene to pachytene transition is crucial for the selection of DNA repair pathways, subsequent activation of meiosis-related genes, sex chromosome paring, and ultimately, male fertility.