In vitro spermatogenesis: A long journey to get tails

The generation of functional sperm in vitro has been a goal for almost a century. Until recently, researchers have only succeeded in reproducing the early steps of spermatogenesis. This is not surprising given that spermatogenesis is a complicated process that requires the coordinated efforts of germ cells and several somatic cells within the tubular structure of the testis. Finally—last year—Sato et al. reported the successful in vitro production of functional sperm, thereby potentially opening up a new era of reproductive biology. Here, we summarize the history of research directed toward reproducing steps of spermatogenesis in vitro, detail the seminal findings of Sato et al., and suggest ways that their approach can be applied toward clinical applications and addressing fundamental questions about the underlying mechanism of spermatogenesis.