Scientists Yoshino et al. developed stem cells from pluripotent cells that mimic a functional mouse testis and support the development of germ cell nails.[1] These cells generate populations of Sertoli cells, Leydig cells, and germ cells.[1] Modulation of BMP and WNT signals exclusively induced SOX9-positive supporting cells from XY cells, accompanied by the formation of seminiferous tubule-like structures containing Sertoli and interstitial cells.[2] Transcriptome analyzes at the single-cell level have shown that differentiation in vitro corresponds to the process of sex determination in vivo, with a male-specific population enriched in Sry, Sox9, Amh, and Dmrt1 genes.[2] The reconstituted testis tissue promoted the differentiation of pluripotent germ cells into spermatogonial stem cells, which produced functional sperm after transplantation into the testis.[2] Sertoli and Leydig-like cells restored testicular function in mice lacking these cell types.[1] The model reconstructs sex determination and the testicular niche without using embryonic tissue.[2]