Meiosis is the first stage of spermatogenesis in which a spermatogonial cell embarks on the process of halving its DNA content in preparation for fertilization. The goal of this proposal isto investigate the onset of meiosis as a possible intervention point for male contraceptive therapies. Using a novel high-throughput CRISPR/Cas9-based mutagenesis method, we will develop an in vitro spermatogonial stem cell (SSC) culture system to identify genes required for entry into meiosis, at the same time establishing this method as a platform for testing drugs that interfere with this transition.