PPP6R3-mediated dephosphorylation regulates mRNA translation during spermatogonial differentiation

Protein dephosphorylation mediated by phosphatases regulates spermatogenesis. However, which proteins are dephosphorylated and how they regulate spermatogenesis are largely unknown. Here, we show that germline-specific deletion of protein phosphatase 6 regulatory subunit 3 (PPP6R3), which determines substrate specificity of protein phosphatase 6 catalytic subunit, causes abnormal spermatogonial differentiation and male infertility, accompanied by translation inhibition. PPP6R3 directly interacts with EIF3C and EIF4G1 in KIT+ spermatogonia. Decreased levels of non-phosphorylated EIF3C and EIF4G1 after PPP6R3 deletion attenuate their enrichment for mRNAs associated with spermatogonial differentiation, and increased phosphorylation levels promote their degradation. Specifically, the phosphorylation status both of EIF3CS39 and EIF4G1S1217 are significantly upregulated in mutant mice. Overexpression of EIF3CS39A and EIF4G1S1217A mutants in Ppp6r3-cKO spermatogonial progenitor cells compensates for their differentiation efficiency by upregulating the translation rates of differentiation-associated mRNAs. Our findings demonstrate that dephosphorylation of EIF3C and EIF4G1 mediated by PPP6R3 is critical for translation activation during spermatogonial differentiation.