YTHDC2 control of gametogenesis requires helicase activity but not m(6)A binding

In this study, Saito et al. sought to understand how the N-6-methyladenosine (m(6)A) reader and RNA helicase YTHDC2 switches cells from mitotic to meiotic gene expression programs. Their findings provide insight into YTHDC2's mechanism, and they propose a model in which YTHDC2 binds transcripts independent of m(6)A status and regulates gene expression during multiple stages of meiosis by distinct mechanisms. Mechanisms regulating meiotic progression in mammals are poorly understood. The N-6-methyladenosine (m(6)A) reader and 3 ' -> 5 ' RNA helicase YTHDC2 switches cells from mitotic to meiotic gene expression programs and is essential for meiotic entry, but how this critical cell fate change is accomplished is unknown. Here, we provide insight into its mechanism and implicate YTHDC2 in having a broad role in gene regulation during multiple meiotic stages. Unexpectedly, mutation of the m(6)A-binding pocket of YTHDC2 had no detectable effect on gametogenesis and mouse fertility, suggesting that YTHDC2 function is m(6)A-independent. Supporting this conclusion, CLIP data defined YTHDC2-binding sites on mRNA as U-rich and UG-rich motif-containing regions within 3 ' UTRs and coding sequences, distinct from the sites that contain m(6)A during spermatogenesis. Complete loss of YTHDC2 during meiotic entry did not substantially alter translation of its mRNA binding targets in whole-testis ribosome profiling assays but did modestly affect their steady-state levels. Mutation of the ATPase motif in the helicase domain of YTHDC2 did not affect meiotic entry, but it blocked meiotic prophase I progression, causing sterility. Our findings inform a model in which YTHDC2 binds transcripts independent of m(6)A status and regulates gene expression during multiple stages of meiosis by distinct mechanisms.