Figure 6

Figure 6

A proposed model. Stc1a plays dual roles in ionocytes. Stc1a suppresses local IGF signaling and inhibits NaR cell proliferation by inhibiting Papp-aa-mediated Igfbp5a degradation. Stc1a also inhibits Trpv6 expression and activities. These two functions are linked. Trpv6-mediated calcium signaling inhibits IGF signaling, while IGF signaling upregulates Trpv6 expression. A loss of Stc1a reactivates IGF-PI3 kinase-Akt-Tor signaling in NaR cells and increased NaR cell proliferation. In addition, Trpv6 expression and Trpv6-mediated calcium uptake in each NaR cell are elevated in the stc1a^-/- mutant fish. These changes contribute to abnormal calcium deposits in the yolk sac region and kidney and to the developemnt of cardiac edema, body swelling, and premature death phenotypes.