Genetic interaction between Bardet-Biedl syndrome genes and implications for limb patterning

Abstract

Bardet-Biedl syndrome (BBS) is a pleiotropic, genetically heterogeneous disorder characterized by obesity, retinopathy, polydactyly, cognitive impairment, renal and cardiac anomalies, as well as hypertension and diabetes. Multiple genes are known to independently cause BBS. These genes do not appear to code for the same functional category of proteins; yet, mutation of each results in a similar phenotype. Gene knockdown of different BBS genes in zebrafish shows strikingly overlapping phenotypes including defective melanosome transport and disruption of the ciliated Kupffer's vesicle. Here, we demonstrate that individual knockdown of bbs1 and bbs3 results in the same prototypical phenotypes as reported previously for other BBS genes. We utilize the zebrafish system to comprehensively determine whether simultaneous pair-wise knockdown of BBS genes reveals genetic interactions between BBS genes. Using this approach, we demonstrate eight genetic interactions between a subset of BBS genes. The synergistic relationships between distinct combinations are not due to functional redundancy but indicate specific interactions within a multi-subunit BBS complex. In addition, we utilize the zebrafish model system to investigate limb development. Human polydactyly is a cardinal feature of BBS not reproduced in BBS-mouse models. We evaluated zebrafish fin bud patterning and observed altered Sonic hedgehog (shh) expression and subsequent changes to fin skeletal elements. The SHH fin bud phenotype was also used to confirm specific genetic interactions between BBS genes. This study reveals an in vivo requirement for BBS function in limb bud patterning. Our results provide important new insights into the mechanism and biological significance of BBS.

BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family chaperonins and mediate BBSome assembly

“…Size exclusion chromatography was performed using Superose-6 10/300 GL column (GE Healthcare). MO injection and analysis of KV and melanosome transport in zebrafish was performed as previously described (14,15). For details, please see SI Materials and Methods.…”

“…We previously demonstrated that knockdown of BBS genes results in the reduction or loss of Kupffer's vesicle (KV) and delays in melanosome transport. These phenotypes are shared among all BBS genes tested (14,15,31). To test whether knockdown of cct genes in zebrafish results in these BBS phenotypes, we designed anti-sense morpholino oligonucleotides (MOs) directed against the cct1, cct2 and cct3 transcription start sites.…”

“…At the molecular level, BBS proteins are involved in protein/vesicle trafficking along microtubules. For example, knockdown of BBS genes in zebrafish results in delay in retrograde melanosome transport, which is mediated by dynein motor proteins along the microtubule (14,15). In C. elegans, mutations in bbs1, bbs7, or bbs8 cause defects in the movement of the intraflagellar transport (IFT) subcomplexes inside the cilium (16).…”

Small organelle, big responsibility: the role of centrosomes in development and disease

“…Laterality defects are also present owing to shorter motile primary cilia in the Kupffer vesicle, an embryonic organ required for left-right asymmetry [129]. Such defects also occur in CEP290-and BBS4-depleted zebrafish, with the former exhibiting additional retinal anomalies [130,131]. Ofd1 is located on the X chromosome both in mice and humans.…”

End Stage Renal Disease, Differential Diagnosis, A Rare Genetic Disorder: Bardet–Biedl Syndrome: Case Report and Review

“…Post axial Polydactyly: Polydactyly may involve all the four limbs, the hands or the feet alone approximately in 21% of cases. Aberrant Sonic-hedgehog signalling has been suggested to account for features of polydactyly of BBS [11]. 3.…”