Evolutionarily Distinctive Transcriptional and Signaling Programs Drive Human Germ Cell Lineage Specification from Pluripotent Stem Cells

Germline specification underlies human reproduction and evolution, but it has proven difficult to study in humans since it occurs shortly after blastocyst implantation. This process can be modeled with human induced pluripotent stem cells (hiPSCs) by differentiating them into primordial germ cell-like cells (hPGCLCs) through an incipient mesoderm-like cell (iMeLC) state. Here, we elucidate the key transcription factors and their interactions with important signaling pathways in driving hPGCLC differentiation from iPSCs. Germline competence of iMeLCs is dictated by the duration and dosage of WNT signaling, which induces expression of EOMES to activate SOX17, a key driver of hPGCLC specification. Upon hPGCLC induction, BMP signaling activates TFAP2C in a SOX17-independent manner. SOX17 and TFAP2C then cooperatively instate an hPGCLC transcriptional program, including BLIMP1 expression. This specification program diverges from its mouse counterpart regarding key transcription factors and their hierarchies, and it provides a foundation for further study of human germ cell development. [Display omitted] •WNT signaling activates EOMES to induce SOX17 expression for hPGCLC specification•The duration of WNT signaling and EOMES expression determines germ cell competence•SOX17 and TFAP2C establish the hPGCLC program in an interdependent fashion•hPGCLC specification exhibits substantial evolutionary divergence from mouse PGCs The mechanisms driving human germ cell specification are largely unknown. Kojima et al. define the signaling and transcriptional programs that drive human germ cell specification in vitro, which show substantial evolutionary divergence from mouse programs. These findings serve as a foundation for further reconstitution of human germ cell development.