Stereotypical interciliary contacts in a C. elegans sense organ

Physical interactions among cells and their processes are critical for intercellular communication and the generation of ordered tissue patterns. Primary cilia projecting from the cell surface have recently been shown to form contacts with the processes of diverse cell types, as well as with other cilia, in the brain and other organs. Whether these ciliary contacts are established in an instructive manner or are formed passively due to physical proximity is unclear. Ultrastructural analyses previously showed that the cilia of a subset of sensory neurons in the head amphid organs of C. elegans exhibit interciliary contacts within a glia-defined channel. Here we show that these ciliary contact patterns are stereotyped and can be re-established in the adult in the absence of neighboring cilia, indicating that these associations may not simply reflect relative positioning within the amphid channel. We show that mutations in a subset of genes implicated in ciliary protein trafficking, ciliary membrane phospholipid composition, and cilia-cell interactions disrupt both cilia structure and interciliary contacts. However, in a subset of mutants, cilia with altered morphologies can nevertheless establish correct contacts, implying that these contacts may be established via a regulated process. Together, our findings suggest that cilia-cilia interactions within a sense organ are established via defined mechanisms and raise the possibility that cilia-mediated intercellular communication may modulate cellular functions.