Functional redundancy of WDR31 with GTPase-activating proteins ELMOD and RP2 in regulating IFT trains via BBSome

The correct intraflagellar transport (IFT) assembly at the ciliary base and the IFT turnaround at the ciliary tip are key for the IFT to perform its function, but we still have poor understanding about how these processes are regulated. Here, we identify WDR31 as a new ciliary protein, and analysis from zebrafish andCaenorhabditis elegansreveals the role ofWDR31in regulating the cilia morphology. We find that loss of WDR-31 together with RP-2 and ELMD-1 (the sole ortholog ELMOD1-3) results in ciliary accumulations of IFT Complex B components and KIF17 kinesin, with fewer IFT/BBSome particles traveling along cilia in both anterograde and retrograde directions, suggesting that the IFT/BBSome entry into cilia and exit from cilia are impacted. Furthermore, anterograde IFT in the middle segment travel at increased speed inwdr-31;rpi-2;elmd-1. Remarkably, a non-ciliary protein leaks into cilia ofwdr-31;rpi-2;elmd-1possible due to IFT defects. This work reveals WDR31-RP-2-ELMD-1 as IFT and BBSome trafficking regulators.