Cfap300 regulates the transdifferentiation of Corpuscle of Stannius cells in zebrafish

Stanniocalcin 1 (Stc1) is a hormone secreted by the Corpuscle of Stannius (CS) gland in teleost fish, including zebrafish, where it regulates calcium homeostasis. The CS gland forms by transdifferentiation of pronephric tubule epithelial cells at the distal early (DE) and distal late (DL) boundary. Although transdifferentiation is known in development and disease, the underlying mechanisms remain unclear. Here, we show that cfap300, a DNAAF implicated in primary ciliary dyskinesia (PCD), is essential for CS gland formation. TALEN-generated cfap300 mutants develop normally and show no nephron segmentation defects, but exhibit impaired CS development, which could be partially rescued by cfap300 mRNA injection. Further, cfap300 mutants display increased expression of cdh17 driven by Hnf1ba, which blocks CS precursor transdifferentiation. Knockdown of cdh17 or hnf1ba restores CS formation. These results uncover a Cfap300-Hnf1ba-Cdh17 pathway that regulates epithelial-to-endocrine transdifferentiation, revealing a novel, lineage-specific role for a DNAAF protein in endocrine organogenesis.