Genetic evidence for Amh modulation of gonadotropin actions to control gonadal homeostasis and gametogenesis in zebrafish and its noncanonical signaling through Bmpr2a receptor.

Anti-Müllerian hormone (Amh) plays an important role in gonadal function. Amh deficiency causes severe gonadal dysgenesis and dysfunction in zebrafish, with gonadal hypertrophy in both sexes. However, its mechanism of action remains unknown. Intriguingly, the Amh cognate type II receptor (Amhr2) is missing in the zebrafish genome, in sharp contrast to other species. Using a series of zebrafish mutants (amh, fshb, fshr and lhcgr), we provided unequivocal evidence for actions of Amh, via modulation of gonadotropin signaling, on both germ cell proliferation and differentiation. The gonadal hypertrophy in amh mutants was abolished in the absence of Fshr in females or Fshr/Lhcgr in males. Furthermore, we demonstrated that knockout of bmpr2a, but not bmpr2b, phenocopied all phenotypes of the amh mutant in both sexes, including gonadal hypertrophy, hyperproliferation of germ cells, retarded gametogenesis and reduced fshb expression. In summary, the present study provided comprehensive genetic evidence for an intimate interaction of gonadotropin and Amh pathways in gonadal homeostasis and gametogenesis and for Bmpr2a as the possible missing link for Amh signaling in zebrafish.

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