Knockdown of Bardet-Biedl Syndrome Gene BBS9 Leads to Primary Cilia Defects and Retinal Degeneration in the Zebrafish

Abstract

Purpose: : To investigate the role of BBS9 in primary cilia and retinal development in the zebrafish. Bardet-Biedl Syndrome (BBS; MIM#209900) is a genetically heterogeneous disorder with pleiotropic phenotypes that include retinopathy, mental retardation, obesity, polydactyly, and renal abnormalities. Of the 15 genes identified so far, seven encode core proteins that form a stable complex called BBSome, which is implicated in cilia biogenesis. Though BBS9 is a component of BBSome complex, it’s function has not yet been delineated.

Methods: : Knockdown of BBS9 was done using either shRNAi in IMCD3 cells or anti-sense morpholino in the zebrafish. Rescue experiments were done in zebrafish using human wild type or missense mutant mRNA.

Results: : Knockdown of BBS9 in mouse IMCD3 cells resulted in absence of cilia. In the zebrafish, anti-sense morpholinos against bbs9 led to developmental abnormalities in the eye, consistent with the phenotypes observed in syndromic ciliopathies. Knockdown of bbs9 also caused reduced number and length of cilia in Kupffer’s vesicle. Furthermore, an orthologous human BBS9 mRNA but not a missense mutant rescued the bbs9 morphant phenotype, confirming the evolutionary conservation between zebrafish and human.

Conclusions: : Our data demonstrate a key role for BBS9 in photoreceptor development of zebrafish due to its functions associated with primary cilia.

Keywords: retinal degenerations: hereditary • retinal development • retinal degenerations: cell biology