Abstract
Purpose: :
Mutations in genes that encode cilia proteins are increasingly recognized as common causes of disease. Cilia defects are also seen as the underlying cause of a number of inherited disorders which affect multiple organ systems, known as ciliopathies such as Bardet-Biedl syndrome, (BBS), in which RP is found in association with multiple cilia-related disorders, including cystic renal disease, polydactyly, mental retardation, obesity and diabetes, gonadal malformations, and situs inversus. Using both in vitro and in vivo approaches, we modeled a ciliopathy by knocking down the novel cilia gene TTC26 and characterizing the resultant phenotypes in renal epithelial cells, zebrafish eyes and pronephoric kidneys.
Methods: :
Mouse Ttc26 was cloned in a V5-N-terminal fusion expression vector which was transfected in mIMCD3 cells and the location was revealed by anti-V5 tag antibody. Fusion protein location in rodent photoreceptor cells was detected by in vivo electrophoration in neonatal rat and followed by immunocytochemistry. Phenotypes of ttc26-morpholino knockdown zebrafish were characterized by histology and EM.
Results: :
Ttc26 localized to the transition zone of photoreceptor cells and the transition zone and cilia in cultured mIMCD3 renal cells. Knockdown of Ttc26 in mIMCD3 cell produced shortened and defect primary cilia, revealed by immunofluorescence and scanning EM respectively. To study its function in sensory cilia in vivo, we utilized a vertebrate model of zebrafish with morphalino knockdown. We observed a motile cilia defect in the pronephric kidney at 27 hpf and a kidney cyst formation with edema at later stages. In the eyes, retinal lamination in the morphants was normal at P5, but photoreceptor outer segments were shortened or absent, indicating that the loss of ttc26 function disrupts ciliogenesis in photoreceptor cells.
Conclusions: :
These data indicate TTC26 is a component of photoreceptor and renal cilia, and suggest that TTC26 is required for normal cilia development and differentiation in the retina and pronephros. These results support screening the TTC26 gene for mutations in human ciliopathies.
Keywords: photoreceptors • visual development • differentiation