Scientists have developed a mouse pluripotent stem cell-based system that reconstitutes testicular somatic cells and the sex determination process in vitro[1]. This system generated the cell types that form the seminiferous tubules and adjacent interstitial tissues, thereby mimicking the development of the testes[1]. The reconstituted tissue promoted the differentiation of primordial germ cell-derived pluripotent stem cells into spermatogonial stem cells[1]. When transplanted into the testes of infertile recipient mice, these cells resumed spermatogenesis and produced mature sperm capable of fertilization, resulting in healthy and fertile offspring[1]. Differentiation of SOX9-positive cells required the presence of the Y chromosome, while FOXL2-positive cells also arose from XY cells and promoted oogenesis, demonstrating an asymmetry between the male and female sex-determination pathways[1]. The study thus created a model of testicular development without the use of embryonic tissue, allowing the analysis of gonadal development and interactions between germ and somatic cells[1].