The in vitro generation of germ cells from pluripotent stem cells (PSCs) can have a substantial effect on future reproductive medicine and animal breeding. A decade ago, in vitro gametogenesis was established in the mouse. However, induction of primordial germ cell–like cells (PGCLCs) to produce gametes has not been achieved in any other species. Here, we demonstrate the induction of functional PGCLCs from rat PSCs. We show that epiblast-like cells in floating aggregates form rat PGCLCs. The gonadal somatic cells support maturation and epigenetic reprogramming of the PGCLCs. When rat PGCLCs are transplanted into the seminiferous tubules of germline-less rats, functional spermatids—that is, those capable of siring viable offspring—are generated. Insights from our rat model will elucidate conserved and divergent mechanisms essential for the broad applicability of in vitro gametogenesis.

Primordial germ cells (PGCs), the founder cells of the germline, are specified in pre-gastrulating embryos in mammals, and subsequently migrate towards gonads to mature into functional gametes. Here, we investigated PGC development in rats, by genetically modifying Prdm14, a unique marker and a critical PGC transcriptional regulator. We trace PGC development in rats, for the first time, from specification until sex determination stage in fetal gonads using Prdm14 H2BVenus knock-in rats. We uncover that Prdm14’s crucial role in PGC specification is conserved between rat and mice, by analyzing Prdm14 deficient rat embryos. Notably, loss of Prdm14 completely abrogates the PGC program: failure in maintenance and/or activation of germ cell markers and pluripotency genes. Finally, we profile the transcriptome of the postimplantation epiblast and all PGC stages in rat, to reveal enrichment of distinct gene sets at each transition point, thereby providing an accurate transcriptional time-line for rat PGC development. Thus, the novel genetically modified rats and data sets obtained in this study will advance our knowledge on conserved vs species-specific features for germline development in mammals.

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Epigenetic signatures of germline cells are dynamically reprogrammed to induce appropriate differentiation, development and sex specification. We investigated sex-specific epigenetic changes in mouse fetal germ cells (FGCs) and neonatal germ cells. Materials & methods: Six histone marks in mouse E13.5 FGCs and P1 neonatal germ cells were analyzed by chromatin immunoprecipitation and sequencing. These datasets were compared with transposase-accessible chromatin sites, DNA methylation and transcriptome. Results: Different patterns of each histone mark were detected in female and male FGCs, and H3K4me3/H3K27me3 bivalent marks were enriched in different chromosomal regions of female and male FGCs. Conclusion: Our results suggest that histone modifications may affect FGC gene expression following DNA methylation erasure, contributing to the differentiation into female and male germ cells.