A WDR35-dependent coatomer transports ciliary membrane proteins from the Golgi to the 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 and across the diffusion barrier 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 IFT-A peripheral components are degraded and core components accumulate at the transition zone. We reveal deep sequence homology and structural similarity of WDR35 and other IFT-As to the coatomer COPI proteins α and β ′, and demonstrate an accumulation of coat-less vesicles which fail to fuse with Wdr35 mutant cilia. Our data provides the first in-situ evidence of a novel coatomer function for WDR35 likely with other IFT-A proteins in delivering ciliary membrane cargo from the Golgi necessary for cilia elongation.

Phylogenetic profiling and cellular analyses of ARL16 reveal roles in traffic of IFT140 and INPP5E

“…We also examined effects of Arl16 KO on core components of the IFT-B complex, which consists of two core complexes (B1-1 and B1-2) and a peripheral complex (Quidwai et al, 2021; Wang et al, 2021; Yang and Huang, 2019). IFT81 (B1-1) and IFT88 (B1-2) localize along the length of the cilium and are often enriched at the base and tip in MEFs (Quidwai et al, 2021). We observed no differences in the localization of either IFT88 or IFT81 in cilia of Arl16 KO cells (Fig.…”

“…Some exclusive pathways transport specific cargos from the Golgi to the cilium, including rhodopsin and PKD2 (Kim et al, 2014; Ward et al, 2011). Furthermore, recent work has highlighted a Golgi to cilium traffic pathway for ciliary membrane proteins that is regulated by IFT-A (Quidwai et al, 2021).…”

“…These multi-subunit complexes are required for the regulated entry and export of proteins from cilia, acting in concert with another protein complex, the BBSome, at the base of cilia in the transition zone. IFT-A is also required for efficient traffic of ciliary membrane cargos to the cilium, acting as a vesicle coat complex between the Golgi and cilia (Quidwai et al, 2021). While the core and peripheral protein components of IFT-A and IFT-B have been established (e.g., IFT-A is comprised of Ciliary protein content is further regulated by targeting of newly synthesized proteins from the ER to the Golgi to the cilium and recycling of membrane proteins from the plasma membrane to the ciliary membrane either through lateral diffusion or recycling through endosomes, though these pathways are less well understood than traffic within the cilium itself (Carter and Blacque, 2019; Nachury, 2018).…”