The embryonic ontogeny of the gonadal somatic cells in mice and monkeys

In the early fetal stage, the gonads are bipotent and only later become the ovary or testis, depending on the genetic sex. Despite many studies examining how sex determination occurs from biopotential gonads, the spatial and temporal organization of bipotential gonads and their progenitors is poorly understood. Here, using lineage tracing in mice, we find that the gonads originate from a T+ primitive streak through WT1+ posterior intermediate mesoderm and appear to share origins anteriorly with the adrenal glands and posteriorly with the metanephric mesenchyme. Comparative single-cell transcriptomic analyses in mouse and cynomolgus monkey embryos reveal the convergence of the lineage trajectory and genetic programs accompanying the specification of biopotential gonadal progenitor cells. This process involves sustained expression of epithelial genes and upregulation of mesenchymal genes, thereby conferring an epithelial-mesenchymal hybrid state. Our study provides key resources for understanding early gonadogenesis in mice and primates. [Display omitted] •Ontogeny of the gonads in mice and monkeys defined by single-cell transcriptomics•Temporally distinct contribution of T+ descendants to the gonads and related organs•The gonads originate from the T+ primitive streak through posterior intermediate mesoderm•The gonads acquire an epithelial-mesenchymal hybrid state upon specification Sasaki et al. map the ontogenic ancestries of the gonads in mice and monkeys. Remarkably, the gonads originate from a T+ primitive streak through WT1+ posterior intermediate mesoderm, and this process involves sustained expression of epithelial genes and upregulation of mesenchymal genes, thereby conferring an epithelial-mesenchymal hybrid state.