AbstractmiRNAs play important roles during mammalian spermatogenesis. However, the function of most miRNAs in spermatogenesis and the underlying mechanisms remain unknown. Here, we report that miR-202 is highly expressed in mouse spermatogonial stem cells (SSCs), and is oppositely regulated by Glial cell-Derived Neurotrophic Factor (GDNF) and retinoic acid (RA), two key factors for SSC self-renewal and differentiation. We used inducible CRISPR-Cas9 to knockout miR-202 in cultured SSCs, and found that the knockout SSCs initiated premature differentiation accompanied by reduced stem cell activity and increased mitosis and apoptosis. Target genes were identified with iTRAQ-based proteomic analysis and RNA sequencing, and are enriched with cell cycle regulators and RNA-binding proteins. Rbfox2 and Cpeb1 were found to be direct targets of miR-202 and Rbfox2 but not Cpeb1, is essential for the differentiation of SSCs into meiotic cells. Accordingly, an SSC fate-regulatory network composed of signaling molecules of GDNF and RA, miR-202 and diverse downstream effectors has been identified.
SummaryMeiosis is the key step in gametogenesis. However, the mechanism of mammalian meiosis remains poorly understood due to the lack of an in vitro model. Here, we report that retinoic acid (RA) is sufficient for inducing leptotene/zygotene spermatocytes from cultured mouse spermatogonial stem cells. Multiple genes regulated by RA were identified by RNA sequencing. RA in combination with pup Sertoli cell co-culture resulted in a higher induction efficiency of 28%. Comparisons in the transcriptomic profiles of the induced spermatogenic cells and the isolated ones revealed the progressive induction of the germ cells. Using this model, we showed that Stra8, Agpat3, Fam57a, Wdr91, and Sox30 contributed to the proliferation and meiosis initiation differentially. In conclusion, we have efficiently generated spermatocytes using an RA/pup Sertoli cell-based in vitro model and provided proof-of-concept evidence for its application in identifying genes involved in mammalian meiosis.
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