The mouse cytosine-5 RNA methyltransferase NSun2 is a component of the chromatoid body and required for testis differentiation

Post-transcriptional regulatory mechanisms are crucial for protein synthesis during spermatogenesis and often organized by the chromatoid body. Chromatoid bodies are large cytoplasmic ribonucleoprotein granules, whose precise function and composition remain unclear. Here, we identify NSun2 as a novel component of the chromatoid body, and further show that this RNA methylase is essential for germ cell differentiation in the mouse testis. Lack of NSun2 leads to down-regulation of genes controlling RNA processing and post-transcriptional repression pathways, including Ddx4, Mili, Piwil1 (Miwi) and Tudor domain containing (Tdrd) proteins. Germ cell differentiation was blocked specifically at the pachytene stage by lack of NSun2, as spermatogonial and Sertoli cells were unaffected in knockout mice. We observed the same phenotype when we simultaneously deleted NSun2 with Dnmt2, the only other characterized cytosine-5 RNA methyltransferase to date, indicating that Dnmt2 was not functionally redundant for NSun2 in spermatogonial stem cells or Sertoli cells. Thus, our data indicate that RNA methylation pathways play an essential role in male germ cell differentiation. Four sample groups: Testes from Wild-type and NSun2 knock out mice at 15 and 49 days; 6 samples in each group