Cap 2′-O-methyltransferase CMTR2 regulates male meiosis independent of its methyltransferase activity

Non-obstructive azoospermia represents one of the most intractable forms of male infertility, with its onset frequently associated with meiotic abnormalities. To date, the pivotal molecular mechanisms governing meiosis remain incompletely understood. This study demonstrates that CMTR2 (Cap methyltransferase 2) exerts a critical regulatory function in male germ cell meiosis through a mechanism independent of its methyltransferase activity. Germ cell-specific Cmtr2 knockout mice (Ddx4-GcKO) exhibited meiotic prophase I zygotene arrest and male sterility. Ddx4-GcKO spermatocytes displayed phenotypic abnormalities, including defective DNA double-strand break repair and compromised crossover formation and recombination. Subsequent investigations revealed a marked reduction in the messenger RNA (mRNA) stability of key meiotic genes, Speedy/RINGO cell cycle regulator family member A (Spdya) and moloney leukemia virus 10 Like 1 (Mov10l1), in Ddx4-GcKO testes. Mechanistic studies indicated that CMTR2 directly interacts with the 5' untranslated regions of these genes. Importantly, CMTR2 selectively mediates 2'-O-methylation of Spdya mRNA, whereas its regulation of Mov10l1 mRNA stability is independent of its enzymatic activity. This study is the first to uncover the non-canonical role of CMTR2 in meiotic regulation, enhancing our comprehension of meiotic molecular mechanisms and offering novel insights into the etiology of male sterility.