Piecing together a ciliome

Cilia are slender microtubule-based appendages that emanate from the surfaces of a large proportion of eukaryotic cells. The motile and non-motile forms of cilia represent bona fide organelles comprising distinct repertoires of proteins that serve specific roles in locomotion or fluid movement, and sense chemical or physical extracellular cues. Owing in part to the growing number of genes associated with ciliary disorders, such as polycystic kidney disease and Bardet-Biedl syndrome, there has been a recent profusion of studies aimed at unveiling the protein makeup of cilia. The approaches used are complementary, involving several different organisms and spanning the fields of bioinformatics, genomics and proteomics. Here we review these studies and assess the various data sets to help define a comprehensive ciliary proteome, or 'ciliome'. We have compiled a cilia protein database that includes known cilia-associated proteins and numerous putative ciliary proteins including RAB-like small GTPases, which might be implicated in vesicular trafficking, and the microtubule-binding protein MIP-T3, some of which might be associated with ciliopathies.