The germ cell-specific RNA binding protein RBM46 is essential for spermatogonial differentiation in mice

Author summaryMale fertility relies upon continuous daily production of millions of fertilization-competent sperm. These sperm are created in the testis during spermatogenesis, the developmental program founded upon spermatogonial stem cells (SSCs). SSCs divide to produce progeny spermatogonia that either remain in the stem cell pool or commit to differentiate and enter meiosis and ultimately form sperm. The balance between stem cell self-renewal and production of gametes is controlled by changes in the expression of a large complement of genes. An emerging concept in control over gene expression is the essential role of proteins that bind to mRNAs and regulate their stability, storage, and/or translation into proteins. Here, we identify such an RNA binding protein-RBM46 -that is only expressed in the male and female germline and required for gamete production and thus fertility in both sexes. In male mice with a specific deletion of Rbm46, spermatogenesis is arrested at spermatogonial differentiation. RBM46 binds a specific cohort of mRNAs encoding factors essential for differentiation and meiosis, and is thus positioned to play a critical role in post-transcriptional control over gene expression in mammalian spermatogonia. Control over gene expression is exerted, in multiple stages of spermatogenesis, at the post-transcriptional level by RNA binding proteins (RBPs). We identify here an essential role in mammalian spermatogenesis and male fertility for 'RNA binding protein 46' (RBM46). A highly evolutionarily conserved gene, Rbm46 is also essential for fertility in both flies and fish. We found Rbm46 expression was restricted to the mouse germline, detectable in males in the cytoplasm of premeiotic spermatogonia and meiotic spermatocytes. To define its requirement for spermatogenesis, we generated Rbm46 knockout (KO, Rbm46(-/-)) mice; although male Rbm46(-/-) mice were viable and appeared grossly normal, they were infertile. Testes from adult Rbm46(-/-) mice were small, with seminiferous tubules containing only Sertoli cells and few undifferentiated spermatogonia. Using genome-wide unbiased high throughput assays RNA-seq and 'enhanced crosslinking immunoprecipitation' coupled with RNA-seq (eCLIP-seq), we discovered RBM46 could bind, via a U-rich conserved consensus sequence, to a cohort of mRNAs encoding proteins required for completion of differentiation and subsequent meiotic initiation. In summary, our studies support an essential role for RBM46 in regulating target mRNAs during spermatogonia differentiation prior to the commitment to meiosis in mice.

Automated summary

Male fertility relies on the continuous production of sperm. Gene expression regulation plays a crucial role in controlling the balance between stem cell self-renewal and gamete production. In this study, an RNA binding protein-RBM46 was identified, which is essential for gamete production and fertility. It binds to specific mRNAs encoding proteins required for differentiation and meiosis during spermatogenesis.