A WDR35-dependent coat protein complex transports ciliary membrane cargo vesicles to cilia

Abstract

Intraflagellar transport (IFT) is a highly conserved mechanism for motor-driven transport of cargo within cilia, but how this cargo is selectively transported to cilia is unclear. WDR35/IFT121 is a component of the IFT-A complex best known for its role in ciliary retrograde transport. In the absence of WDR35, small mutant cilia form but fail to enrich in diverse classes of ciliary membrane proteins. In Wdr35 mouse mutants, the non-core IFT-A components are degraded and core components accumulate at the ciliary base. We reveal deep sequence homology of WDR35 and other IFT-A subunits to α and ß' COPI coatomer subunits, and demonstrate an accumulation of 'coat-less' vesicles which fail to fuse with Wdr35 mutant cilia. We determine that recombinant non-core IFT-As can bind directly to lipids and provide the first in-situ evidence of a novel coat function for WDR35, likely with other IFT-A proteins, in delivering ciliary membrane cargo necessary for cilia elongation.

Structure of the ciliogenesis-associated CPLANE complex

“…These vesicles could originate at PRE or another PI(3)P-rich compartment. This hypothesis is supported by the CPLANE interactome ( 19 ), which includes IFT-A subunits and proteins involved in vesicle transport and fusion; moreover, IFT-A proteins can associate with vesicles ( 51 ) and abnormal vesicle accumulation has been observed in mutants of CPLANE proteins or downstream effectors ( 21 , 26 ). The CPLANE complex could, for example, use its multiple PI(3)P binding sites to function as tether and bridge vesicles to target membranes before fusion ( 53 ).…”

“…A parsimonious hypothesis would be that aberrant PI(3)P binding may result in defective vesicle trafficking that perturbs BBS-related protein functions. Such defects could either compromise IFT-A complex assembly and subsequently result in abnormal IFT-B, and hence BBSome ciliary trafficking, or affect other BBS proteins that localize in the cilium transition zone ( 5 , 19 , 51 ). While the mechanistic details remain to be defined, this represents one of the first examples that link perturbed PIP binding with ciliopathies ( 5 ).…”

“…The CPLANE complex could, for example, use its multiple PI(3)P binding sites to function as tether and bridge vesicles to target membranes before fusion ( 53 ). An important prediction of this model would be that CPLANE operates on PI(3)P-rich vesicles with an IFT-A–dependent coat ( 51 ). The main CPLANE PI(3)P binding modules contain intrinsically disordered regions, and this presumably could contribute to the regulation of the CPLANE complex’s functions.…”

Centriolar satellites expedite mother centriole remodeling to promote ciliogenesis

“…Mouse embryonic fibroblasts (MEFs) were maintained as previously published ( Hall et al, 2013 ). SNAP labelling was performed as previously described ( Quidwai et al, 2021 ). Ependymal cells were isolated and cultured as published in ( Delgehyr et al, 2015 ), and imaged 14-20 days post serum withdrawal.…”

“…SNAP labelling was performed as previously described (Quidwai et al, 2021). Ependymal cells were isolated and cultured as published in (Delgehyr et al, 2015), and imaged 14-20 days post serum withdrawal.…”