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Cutting off ciliary protein import: Intraflagellar transport after dendritic femtosecond-laser ablation

    Published Online:https://doi.org/10.1091/mbc.E18-06-0399

    Primary cilia, organelles protruding from the surface of eukaryotic cells, act as cellular antennae to detect and transmit signals from the extracellular environment. They are built and maintained by continuous cycles of intraflagellar transport (IFT), where ciliary proteins are transported between the ciliary base and tip. These proteins originate from the cell body since cilia lack protein synthesis machinery. How input from the cell body affects IFT and ciliary function is not well understood. Here, we use femtosecond laser ablation to perturb the dendritic input of proteins to chemosensory cilia in living C. elegans. Using fluorescence microscopy, we visualize and quantify the real-time response of ciliary proteins to dendritic ablation. We find that the response occurs in three distinct stages. First, IFT dynein is activated within seconds redistributing IFT components towards the ciliary base; second, the ciliary axoneme shortens and motors slow down; and third, motors leave the cilium. Depletion of ATP by adding azide also results in IFT slow-down and IFT components leaving the cilium, but not in activation of retrograde IFT. These results indicate that laser ablation triggers a specific mechanism important for IFT regulation that allows the cilium to rapidly adapt to changes in the outside environment.

    Movie S1: IFT-dynein redistribution and slow-down. Fluorescence movie of pair of phasmid cilia (XBX-1::EGFP strain) pre and post-ablation. Time and scale bar are indicated. Same data as in Figure 2.
    Movie S2: IFT dynein and OSM-3 distribution and dynamics in C. elegans phasmid cilia (strain EJP212) before and after low-concentration azide treatment. Sodium azide is added at t = 0 s. Scale bar, 2 um. Video plays at 5x real time (time indicated). Video corresponds to Figure 4A, third horizontal panel, and Supplemental Figure 2A, third horizontal panel.