Sequential enhancer state remodelling defines human germline competence and specification

Abstract

Germline-soma segregation is a fundamental event during mammalian embryonic development. Here, we establish the epigenetic principles of human primordial germ cell (hPGC) development using in vivo hPGCs and stem cell models recapitulating gastrulation. We show that morphogen-induced remodelling of mesendoderm enhancers transiently confers the competence for hPGC fate, but further activation favours mesoderm and endoderm fates. Consistently, reducing the expression of the mesendodermal transcription factor (TF) OTX2 promotes the PGC fate. In hPGCs, SOX17 and TFAP2C initiate activation of enhancers to establish a core germline program, including the transcriptional repressor PRDM1 and pluripotency factors POU5F1 and NANOG. We demonstrate that SOX17 enhancers are the critical components in the regulatory circuitry of germline competence. Furthermore, activation of upstream cis -regulatory elements by an optimised CRISPR activation system is sufficient for hPGC specification. We reveal an enhancer-linked germline TF network that provides the basis for the evolutionary divergence of mammalian germlines.

Origin and segregation of the human germline

“…Furthermore, we observed upregulation of NANOG (p < 9.26e -48 /1.62e -6 ) and concomitant downregulation of OTX2 (p < 6.48e -10 /0.045) in subcluster 3 compared to non-competent clusters 1 and 22 respectively. Notably, OTX2 negatively regulates PGCLC competence in mice (Zhang et al, 2018) and we recently found that OTX2 has a similar function in the human germline (Tang et al, 2022)…”

“…We investigate how the precursor PreME cells gain competence for PGC-fate to address this. We also analysed the PGC-competent 4i cells against the non-competent populations (PSCs and ME) (Tang et al, 2022).…”

The functional diversity of the POUV-class proteins across vertebrates

“…As it was pointed above, the Sox17-Oct4 complex occupies compressed motifs, which are 1 bp shorter that the canonical Sox2-Oct4 motif [ 121 ]. Analyses of open chromatin during hPGC maturation have revealed the compressed Sox-Oct motif occurs across active DNA elements [ 146 , 147 ]. As Sox17 is associated with endoderm specification, the rationale for Oct4 partner switching from Sox2 to Sox17 in human PGC development remains unclear.…”

Mapping developmental paths of monkey primordial germ-like cells differentiation from pluripotent stem cells by single cell ribonucleic acid sequencing analysis

“…We found that in addition to germ cell fate, the mesoderm and endoderm lineages were induced in the current differentiation system. A study in human PSCs revealed that predifferentiation through premesendoderm intermediate activates mesendoderm enhancers and endows human PSCs with competence for PGCLCs differentiation [ 41 ] and further activation induces mesoderm and endoderm lineage specification, whereas downregulation of mesendodermal marker gene OTX2 promotes the PGC’s fate. Moreover, the synergist interaction of SOX17 and TFAP2C guarantees the PGCLCs’ differentiation [ 41 ].…”

“…A study in human PSCs revealed that predifferentiation through premesendoderm intermediate activates mesendoderm enhancers and endows human PSCs with competence for PGCLCs differentiation [ 41 ] and further activation induces mesoderm and endoderm lineage specification, whereas downregulation of mesendodermal marker gene OTX2 promotes the PGC’s fate. Moreover, the synergist interaction of SOX17 and TFAP2C guarantees the PGCLCs’ differentiation [ 41 ]. Taken together, it is worthy to test whether the same mechanism is used to induce mPGCLCs and the inhibition of the mesoderm and endoderm cell fates using small molecules could further improve the frequency of PGCLC differentiation from primate PSCs.…”