RNA-binding proteins DND1 and NANOS3 coordinately suppress SOX4 in processing bodies for restricting the entry of germ cell lineage

Specification of germ cell fate establishes the germline development during early embryogenesis, yet the underlying mechanisms remain largely unknown in humans. Here we focus on the functional roles of the RNA-binding protein (RBP) DND1 in human germline specification. We deleted the whole genomic region of DND1 in human embryonic stem cells (hESCs), based on which we generated human primordial germ cell-like cells (hPGCLCs). Interestingly, we discovered an increased percentage of hPGCLCs induced from DND1 deleted hESCs, suggesting that DND1 may restrict the specification of human germ cell lineage. Mechanistic investigation reveals that DND1 forms a complex with another RBP NANOS3, in which DND1 facilitates the binding of NANOS3 to their target mRNAs. Furthermore, by analyzing the mRNAs bound by DND1 and NANOS3, we identified SOX4 mRNAs as the key downstream factor for DND1 and NANOS3 complex to restrict the induction of hPGCLCs. Interestingly, DND1 and NANOS3 function in processing bodies (P-bodies) to repress the translation of SOX4 mRNAs, where NANOS3 bridges the interaction between DND1 and the translational repressor 4E-T. Altogether, these findings identify the RBPs DND1 and NANOS3 as “break system” to restrict the entry of germ cell fate in humans.