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.

Intraflagellar transport（IFT）是纤毛内由马达驱动的货物转运的高度保守机制，但货物如何被选择性转运至纤毛尚不清楚。WDR35/IFT121是IFT-A复合物的组分，其最广为人知的作用是参与纤毛逆行转运。在缺乏WDR35的情况下，会形成小型突变纤毛，但无法富集各类纤毛膜蛋白。在Wdr35小鼠突变体中，非核心IFT-A组分发生降解，而核心组分则在纤毛基部积累。我们发现WDR35及其他IFT-A亚基与α和β' COPI衣被蛋白亚基具有深度序列同源性，并证实无衣被囊泡会在Wdr35突变纤毛处积累且无法与之融合。我们确定重组非核心IFT-A蛋白可直接结合脂质，并首次提供原位证据表明WDR35（可能与其他IFT-A蛋白协同）具有新型衣被功能，负责递送纤毛伸长所需的纤毛膜货物。