Gamete formation constitutes the foundation of sexual reproduction. In the embryonic ovary, primordial germ cells must successively cease proliferating, exit the pluripotent state, differentiate into oogonia, and then enter meiosis. This transition follows an intrinsic clock—that is, one independent of the number of cell divisions—whose molecular basis remained largely unknown. Identifying this mechanism represents a major challenge in reproductive biology, since each individual's fertility depends on it. Until now, attention had focused chiefly on retinoic acid, long regarded as the trigger of meiotic entry, but whose role recent work has called into question.
Using murine loss-of-function and gain-of-function models generated by tamoxifen-inducible conditional recombination, the team specifically examined WNT/β-catenin signaling within the germ cells themselves. This approach made it possible to distinguish the pathway's intrinsic action in gonocytes from its indirect effects via the somatic cells of the gonad, a distinction previously impossible. The analyses combined quantification of gene expression by qRT-PCR, immunostaining of pluripotency factors and meiotic markers, and assessment of chromatin accessibility, in ovaries collected between 11.5 and 14.5 days post-coitum.
The results establish that β-catenin activity, intrinsic to germ cells, maintains the pluripotent state and that its repression conditions differentiation and timely entry into meiosis. In the loss-of-function model, germ cells enter meiosis prematurely; conversely, sustained activation of the pathway arrests them in the pluripotent state. The authors further show that the nuclear interaction between β-catenin and the pluripotency factor POU5F1 is associated with the maintenance of pluripotency, whereas the exit of this complex from the nucleus accompanies differentiation. This switch is promoted by increased expression of Znrf3, a negative regulator of WNT/β-catenin signaling. The team also observes that β-catenin modulates chromatin accessibility in gonocytes, bringing its action closer to epigenetic mechanisms already described, such as those of the Polycomb PRC1 complex.
The authors thus propose that the WNT/β-catenin pathway acts as a central checkpoint: it coordinates the timing of somatic cell differentiation and enables gonocytes to become oogonia capable of supporting gametogenesis. Once the pathway is repressed in gonocytes, factors produced under the influence of somatic WNT/β-catenin activity, such as BMP2, permit progression toward meiosis. Beyond advancing our understanding of gametogenesis, this work could shed light on certain causes of infertility as well as the etiology of germ cell tumors, which frequently express pluripotency markers and β-catenin.