Anti-Müllerian hormone (AMH/Amh) plays an important role in gonadal function. Amh deficiency caused severe gonadal dysgenesis and dysfunction in zebrafish with gonadal hypertrophy in both sexes. However, its action mechanism 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 Amh actions via modulating gonadotropin signaling on both germ cell proliferation and differentiation. The gonadal hypertrophy in amh mutants was abolished in the absence of FSH receptor (Fshr) in females or Fshr/LH receptor (Lhcgr) in males. Furthermore, we demonstrated that knockout of bone morphogenetic protein (BMP) type II receptor A (bmpr2a), but not bmpr2b, phenocopied all phenotypes of amh mutant in both sexes, including gonadal hypertrophy, hyper-proliferation 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.

Hippo signaling pathway is a kinase cascade which plays an important role in organ size control. As the main effectors of the Hippo pathway, transcription coactivators Yap1/Wwtr1 are regulated by the upstream kinase Stk3. Recent studies in mammals have implicated Hippo pathway in kidney development and kidney diseases. To further illustrate its roles in vertebrate kidney, we generated a series of zebrafish mutants targeting stk3, yap1 and wwtr1 genes. The stk3−/- mutant exhibited edema, formation of glomerular cysts and pronephric tubule dilation during larval stage. Interestingly, disruption of wwtr1 but not yap1 significantly alleviated the renal phenotypes of the stk3−/- mutant, and overexpression of Wwtr1 with CMV promoter also induced pronephric phenotypes during larval stage, similar to those of the stk3−/- mutant. Notably, adult fish with Wwtr1 overexpression developed phenotypes similar to those of human polycystic kidney disease (PKD). Overall, our studies revealed roles of Stk3 and Wwtr1 in renal cyst formation. Using pharmacological approach, we further demonstrated that Stk3-deficient zebrafish could serve as a PKD model for drug development.