Bardet-Biedl syndrome (BBS) is an archetypal ciliopathy caused by dysfunction of primary cilia. BBS affects multiple tissues, including the kidney, eye and hypothalamic satiety response. Understanding pan-tissue mechanisms of pathogenesis versus those which are tissue-specific, as well as gauging their associated inter-individual variation owing to genetic background and stochastic processes, is of paramount importance in syndromology. The BBSome is a membrane-trafficking and intraflagellar transport (IFT) adaptor protein complex formed by eight BBS proteins, including BBS1, which is the most commonly mutated gene in BBS. To investigate disease pathogenesis, we generated a series of clonal renal collecting duct IMCD3 cell lines carrying defined biallelic nonsense or frameshift mutations in Bbs1, as well as a panel of matching wild-type CRISPR control clones. Using a phenotypic screen and an unbiased multi-omics approach, we note significant clonal variability for all assays, emphasising the importance of analysing panels of genetically defined clones. Our results suggest that BBS1 is required for the suppression of mesenchymal cell identities as the IMCD3 cell passage number increases. This was associated with a failure to express epithelial cell markers and tight junction formation, which was variable amongst clones. Transcriptomic analysis of hypothalamic preparations from BBS mutant mice, as well as BBS patient fibroblasts, suggested that dysregulation of epithelial-to-mesenchymal transition (EMT) genes is a general predisposing feature of BBS across tissues. Collectively, this work suggests that the dynamic stability of the BBSome is essential for the suppression of mesenchymal cell identities as epithelial cells differentiate.

Biochemistry Center University of Heidelberg Im Neuenheimer Feld 328 69120 Heidelberg Germany

BioQuant University of Heidelberg Im Neuenheimer Feld 267 69120 Heidelberg Germany

Great Ormond Street Institute of Child Health University College London London WC1N 1EH UK

Institute for Ophthalmic Research Center for Ophthalmology University of Tübingen Elfriede Aulhorn Strasse 7 72076 Tübingen Germany

Laboratory of Adaptive Immunity Institute of Molecular Genetics of the Czech Academy of Sciences 14220 Prague Czech Republic

Life Sciences Department CHMLS Brunel University London Kingston Lane Uxbridge UB8 3PH UK

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