<i>RAD21L1</i> Is Sufficient and Effective for Reprogramming Human Sertoli Cells to Phenotypic Spermatogonial Stem Cells Through DNA Methylation and Essential for Male Fertility

It remains unknown about molecular mechanisms underlying the transition of somatic cells into male germ cells. It is observed that RAD21L1 transcript is upregulated during reprogramming of Sertoli cells into human spermatogonial stem cells (SSCs) by overexpressing DAZ family genes. Significantly, RAD21L1 overexpression transits Sertoli cells into phenotypic and functional human SSCs with high safety. RNA sequencing shows that DNMT1 is expressed at a higher level by RAD21L1 overexpression when Sertoli cells are reprogrammed to become human SSCs. Whole genome bisulfite sequencing elucidates that RAD21L1 modulates DNA methylation to reprogram Sertoli cells into human SSCs, and RAD21L1 interacts with DNMT1 in human SSCs generated from Sertoli cells. Intriguingly, RAD21L1 mutation results in the decreases in stemness maintenance of human SSCs and DNMT1 expression levels. Notably, RAD21L1 mutations are positively related to risk of non-obstructive azoospermia (NOA) and male infertility. Collectively, these results implicate that RAD21L1 is sufficient and effective for reprogramming human Sertoli cells to SSCs through modulating DNMT1 and RAD21L1 mutations leads to NOA. This study is of particular significance because it provides a novel molecular mechanism that reprograms human somatic cells into human SSCs and it could offer invaluable gametes for treating male infertility.