Molecular and cellular design of ovotestis development

Ovotestis often occurs in intersex individuals under certain pathological and physiological conditions. However, how ovotestis is formed remains unknown. Here, we report the first comprehensive single-cell developmental atlas of the model fish ovotestis. We provide an overview of ovotestis cell identities and a roadmap of germline, niche, and stem cell development in ovotestis by cell lineage reconstruction and a uniform manifold approximation and projection. We identify common progenitors of germline stem cells with two states, which reveal their bipotential nature to differentiate into both spermatogonial stem cells and female germline stem cells. Moreover, we found that ovotestis infertility was caused by developmental defects in oogenesis owing to dynamic autophagic degradation in female germline cells, and in spermatogenesis due to deficiency of histone-to-protamine replacement in spermatid differentiation. Notably, signaling pathways in gonadal niche cells and their interaction with germline cells synergistically determined cell fates of both male and female germlines in ovotestis. Overall, we reveal a cellular fate map of germline and niche cell development that shapes cell differentiation directions of ovotestis, and provide novel insights into ovotestis development.