Tulp3 deficiency results in ciliopathy phenotypes during zebrafish embryogenesis.

Ciliopathies, caused by defective cilia biogenesis or function, comprise a genetically and clinically diverse group of diseases. Primary cilia play pivotal roles in the regulation of a multitude of signalling pathways during development and tissue homeostasis. Cilia assembly, maintenance and signalling depend on intraflagellar transport (IFT). Tubby-like protein 3 (TULP3) functions as an adapter protein for the ciliary trafficking of diverse membrane cargos via an interaction with the IFT-A complex. Recently, we and others have shown that individuals carrying pathogenic TULP3 variants suffer from progressive liver, kidney and heart disease. In line with these findings, adult Tulp3 knockout zebrafish displayed liver fibrosis and kidney cyst phenotypes. In the present study, we analysed the functional consequences of Tulp3 deficiency during zebrafish embryogenesis. Tulp3 deficiency resulted in well-known ciliopathy-associated phenotypes including pronephric cysts, body curvature and altered left-right asymmetry. Our analysis of urotensin 2-related peptide (Urp) signalling, which is required for proper spine morphogenesis, revealed reduced expression of urp1 in Tulp3 knockout embryos. We also observed scoliosis in a significant number of adult Tulp3 knockout zebrafish. Analysis of ciliogenesis revealed a reduced cilia number and ciliary length in Tulp3 deficient embryos. In addition, Tulp3 deficiency resulted in upregulation of cilia-dependent profibrotic Wnt and Jak/Stat signalling components. Furthermore, we demonstrate that loss of Tulp3 causes upregulation of genes related to liver fibrosis. In conclusion, our data highlights a role of Tulp3 in proper cilia formation and function to maintain healthy tissue architecture during zebrafish embryogenesis, and provides further insight into the spectrum of cilia-related phenotypes in adult zebrafish depleted for Tulp3 functions.