ReviewCoordinating the uncoordinated: UNC119 trafficking in cilia

- IFT alone is not sufficient to construct the compositionally distinct ciliary environment.
- UNC119 proteins interact with known molecular switches to traffic proteins to and within the cilium.
- Despite a role for UNC119 in cilia, mutations in unc119 genes in vertebrates only result in retinal disease.
- UNC119 proteins also have other cellular roles in non-cilia contexts.

Constructing the distinct subcellular environment of the cilium relies in a large part upon intraflagellar transport (IFT) proteins, which traffic cargo both to and within the cilium. However, evidence from the last 10 years suggests that IFT alone is not sufficient to generate the ciliary environment. One essential factor is UNC119, which interacts with known IFT molecular switches to transport ciliary cargos. Despite its apparent importance in ciliary trafficking though, human UNC119 mutations have only rarely been associated with diseases commonly linked with ciliopathies. This review will outline the trafficking pathways required for constructing the cilium by highlighting UNC119's role and the complexities involved in ciliary trafficking. Finally, despite important roles for UNC119 in cilia, UNC119 proteins also interact with non-ciliary proteins to affect other cellular processes.