YTHDC2 serves a distinct late role in spermatocytes during germ cell differentiation

Post-transcriptional regulation of gene expression by RNA-binding proteins can enhance the speed and robustness of cell state transitions by controlling RNA stability, localization, or if, when or where mRNAs are translated. The RNA helicase YTHDC2 is required to shut down components of the mitotic program to facilitate a proper switch from mitosis to meiosis in mouse germ cells. Here we show that YTHDC2 has a second essential role in promoting meiotic progression in late spermatocytes. Inducing conditional knockout of Ythdc2 during the first wave of spermatogenesis, after initiation of meiotic prophase, allowed Ythdc2-deficient germ cells to advance to the pachytene stage and properly express many meiotic markers. However, the Ythdc2-deficient spermatocytes mis-expressed a number of genes, some up-regulated and some down-regulated, failed to transition to the diplotene stage, then quickly died. Co-immunoprecipitation experiments revealed that YTHDC2 interacts with several RNA-binding proteins in early or late spermatocytes, with many of the interacting proteins, including MEIOC, localizing to granules, similar to YTHDC2. Our findings suggest that YTHDC2 collaborates with other RNA granule components to facilitate proper progression of germ cells through multiple steps of meiosis via mechanisms influencing post-transcriptional regulation of RNAs. SIGNIFICANCE STATEMENTAn effective, robust switch from mitosis to meiosis is essential for the production of gametes in sexually reproducing organisms. The RNA helicase YTHDC2 is required for germ cells to shut down aspects of the mitotic program as they initiate meiotic prophase in the mouse male germline. Here we utilize a timed conditional knockout strategy to show that, in addition to its conserved function in the mitosis-to-meiosis transition, YTHDC2 has a second critical role in promoting the pachytene-to-diplotene transition late in male meiotic prophase. YTHDC2 interacts with several proteins that are also present in RNA granules, including MEIOC, suggesting that YTHDC2 collaborates with RNA granule components to regulate RNAs as germ cells progress from one cell state to the next.