A novel xeno-organoid approach: exploring the crosstalk between human iPSC-derived PGC-like and rat testicular cells.

Specification of germ cell-like cells from induced pluripotent stem cells has become a clinically relevant tool for research. Research on initial embryonic processes is often limited by the access to foetal tissue, and in humans, the molecular events resulting in primordial germ cell (PGC) specification and sex determination remain to be elucidated. A deeper understanding of the underlying processes is crucial to describe pathomechanisms leading to impaired reproductive function. Several protocols have been established for the specification of human pluripotent stem cell towards early PGC-like cells (PGCLC), currently representing the best model to mimic early human germline developmental processes in vitro. Further sex determination towards the male lineage depends on somatic gonadal cells providing the necessary molecular cues. By establishing a culture system characterized by the re-organization of somatic cells from postnatal rat testes into cord-like structures and optimizing efficient PGCLC specification protocols, we facilitated the co-culture of human germ cell-like cells within a surrogate testicular microenvironment. Specified conditions allowed the survival of rat somatic testicular and human PGCLCs for 14 days. Human cells maintained the characteristic expression of octamer-binding transcription factor 4, SRY-box transcription factor 17, and transcription factor AP-2 gamma and were recovered from the xeno-organoids by cell sorting. This novel xeno-organoid approach will allow the in vitro exploration of early sex determination of human PGCLCs.