Multivalent BBSome-IFT proximities support IFT-A-IFT-B coordination in vivo

Multivalent BBSome–IFT proximities in intact cilia of Caenorhabditis elegans and mammalian cells support IFT-A–IFT-B coordination, with FLIM-FRET mapping placing IFT144 near IFT172 and IFT88.

• Why it matters: Coordinated IFT-A and IFT-B movement is required for ciliary transport, but the in vivo mechanism that keeps these assemblies coupled during dynamic trafficking is unclear.
• What they did: Using endogenous fluorescent knock-in tagging plus quantitative in vivo FLIM-FRET, the study mapped proximity networks within IFT-B and tested BBSome effects with BBSome loss, split-GFP complementation, structural modeling, and charge-reversal mutagenesis.
• The result: BBSome loss is associated with weaker IFT-A–IFT-B proximity signals and divergent subcomplex transport dynamics, and charge-reversal mutations impair BBSome recruitment and functional rescue, supporting the proposed multivalent coordination model.

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