Vesicles clustering around Wdr35-/- cilia lack electron dense decorations although electron-dense clathrin coated vesicles are still observed budding from the mutant plasma membrane (Figure 7- source data 1)

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.