Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, but the underlying mechanism remains hypothetical and is generally proposed to be of neuroendocrine origin. In this study, we show that while the proliferating preadipocytes or mature adipocytes are nonciliated in culture, a typical primary cilium is present in differentiating preadipocytes. This transient cilium carries receptors for Wnt and Hedgehog pathways, linking this organelle to previously described regulatory pathways of adipogenesis. We also show that the BBS10 and BBS12 proteins are located within the basal body of this primary cilium and inhibition of their expression impairs ciliogenesis, activates the glycogen synthase kinase 3 pathway, and induces peroxisome proliferator-activated receptor nuclear accumulation, hence favoring adipogenesis. Moreover, adipocytes derived from BBSpatients' dermal fibroblasts in culture exhibit higher propensity for fat accumulation when compared to controls. This strongly suggests that a peripheral primary dysfunction of adipogenesis participates to the pathogenesis of obesity in BBS.adipogenesis ͉ primary cilium ͉ ciliopathy ͉ obesity

Bardet–Biedl syndrome (BBS), an emblematic disease in the rapidly evolving field of ciliopathies, is characterized by pleiotropic clinical features and extensive genetic heterogeneity. To date, 14 BBS genes have been identified, 3 of which have been found mutated only in a single BBS family each (BBS11/TRIM32, BBS13/MKS1 and BBS14/MKS4/NPHP6). Previous reports of systematic mutation detection in large cohorts of BBS families (n > 90) have dealt only with a single gene, or at most small subsets of the known BBS genes. Here we report extensive analysis of a cohort of 174 BBS families for 12/14 genes, leading to the identification of 28 novel mutations. Two pathogenic mutations in a single gene have been found in 117 families, and a single heterozygous mutation in 17 families (of which 8 involve the BBS1 recurrent mutation, M390R). We confirm that BBS1 and BBS10 are the most frequently mutated genes, followed by BBS12. No mutations have been found in BBS11/TRIM32, the identification of which as a BBS gene only relies on a single missense mutation in a single consanguineous family. While a third variant allele has been observed in a few families, they are in most cases missenses of uncertain pathogenicity, contrasting with the type of mutations observed as two alleles in a single gene. We discuss the various strategies for diagnostic mutation detection, including homozygosity mapping and targeted arrays for the detection of previously reported mutations.

We constructed a synthetic gene encoding the published amino acid sequence of DTx from Dendroaspis angusticeps, a ligand of voltagedependent postassium channels that facilitates neurotransmitter release. We expressed it in Escherichia coli as a fusion protein secreted in the culture medium. The recombinant DTx was generated in vitro by chemical treatment and recovered as two isoforms. One of them (rDTx), like the venom toxin, has an N-terminal pyroglutamate whereas the other (rQDTx) has a free N-terminal glutamine. Chromatographic differences between rDTx and natural DTx led us to re-examine the amino acid sequence of natural DTx. In contrast to what was previously published, position 12 was an Asp and not Asn. Despite this difference, rDTx and DTx had similar toxicity in mice and binding affinity to synaptosomes, suggesting that residue 12 is not important for DTx function. Nor is the N-terminal residue implicated in DTx function since rDTx and QDTx also had similar biological activities. We also synthesized and expressed a mutant of the DTx gene in which the lysine triplet 28-30 was changed into Ala-Ala-Gly. The two resulting recombinant isoforms exhibited only small decreases in biological activity, excluding the possibility that the positively charged lysine triplet 28-30 of DTx is directly involved in the toxin functional site.