Qilin is essential for cilia assembly and normal kidney development in zebrafish

Defects in the cilium, a once thought vestigial organelle, have recently been implicated in many human diseases, including a number of cystic kidney diseases such as polycystic kidney disease (PKD), Bardet Bieldl Syndrome, and Meckel-Gruber Syndrome. In a forward genetic screen, qilin was identified as a novel gene important in the pathogenesis of kidney cysts in zebrafish. In this paper we characterized qilin(hi3959A) mutant's phenotypes in detail, investigated cilia formation in this mutant and performed structural and functional analysis of the Qilin protein. Results reveal Qilin's essential role in cilia assembly and maintenance in multiple organs, including the kidney, the lateral line organ, and the outer segment of the photoreceptor cell. In addition, rescue experiments suggest that defective pronephric cilia correlate with the formation of kidney cysts in qilin(hi3959A) mutants. Further, genetic analysis suggests that qilin interacts with multiple intraflagellar transport (IFT) complex B genes, which is supported by the striking phenotypic similarities between qilin(hi3959A) and IFT complex B mutants. Finally, through deletion analysis we provide evidence that the well-conserved N-terminus and the coiled-coil domain of Qilin are both essential and sufficient for its function. Taken all the observations together, we propose that Qilin acts in a similar role as IFT complex B proteins in cilia assembly, maintenance and kidney development in zebrafish.