A Signaling and Transcription Architecture for the Specification of Human Germ Cell Lineage. Homo sapiens

The mechanism for human germ-cell specification, which sets out a complex program generating spermatozoa or oocytes, remains largely unknown. We established a system for inducing human primordial germ cell-like cells (hPGCLCs) from induced pluripotent stem cells (hiPSCs) via incipient mesoderm-like cells (iMeLCs). Here, we show that EOMESODERMIN (EOMES) elevates in iMeLCs through WNT signaling and is essential for activating SOX17, a key driver for hPGC(LC) specification, with the duration/dosage of the WNT signaling/EOMES expression dictating the germ-cell competence. Upon hPGCLC induction, BMP signaling activates TFAP2C independently from SOX17, and SOX17 and TFAP2C instate the hPGCLC program, including BLIMP1 expression, in an interdependent fashion. The hPGC(LC) specification program is highly consistent with the monkey program, but is divergent from the mouse one regarding key transcription factors and their hierarchy of actions. These findings delineate evolutionary divergence of mammalian germ-cell specification, providing a foundation for further human germ-cell development in vitro. Overall design: RNAseq analysis of hiPSCs, iMeLCs and hPGCLCs in multiple knockout/rescued lines