Primary cilia are present on all sensory neurons and are critical for their functions. The organization of neurons and their processes within neuropils has been shown to be important for their functions in multiple organisms. However, whether the organization of cilia within a sense organ is similarly important for sensory neuron function is unclear. In C. elegans, the cilia of eight chemosensory neurons of the head amphid sense organs are present within a channel formed by surrounding glia. Previous work from the Sengupta lab showed that these cilia are stereotypically arranged within this channel and form specific contacts with one another. We found that
sax-7 mutants, which have altered amphid neuron dendrite order, retain stereotypical cilia organization within this channel, suggesting cilia arrangement is not a consequence of dendrite order. Cilia-cilia contact appears to be dependent on the presence of ciliary distal segments. Because flagella adhesion during Chlamydomonas mating is mediated by glycoproteins, we asked whether glycoproteins might control ciliary organization and cilia-cilia contact in C. elegans. Our preliminary results indicate that mutations in an enzyme involved in synthesizing N-linked glycoproteins alters ciliary organization and cilia-cilia contact. In a screen of candidate regulators of cilia organization, we identified the conserved phogrin homolog IDA-1. Mutations in
ida-1 alter cilia position within the amphid channel. IDA-1 localizes to the ciliary base; however, mutations in the BBSome protein BBS-7 mislocalize IDA-1 to the cilia. To determine whether IDA-1 localization is critical for regulating ciliary position, we examined the cilia of
bbs-7 mutants. Our preliminary results indicate that cilia in these animals are also disorganized. Additionally, the cilia-cilia contacts typically seen in wild-type animals may be altered in
bbs-7 mutants. IDA-1 is a transmembrane protein localized to the membrane of dense-core vesicles (DCVs) and is implicated in regulating DCV cargo release. Mutations in
unc-31 disrupt DCV exocytosis, however, the cilia of
unc-31 mutants appear largely wild-type, suggesting that
ida-1 control of ciliary organization is independent of its role in DCV signaling. Our current experiments are aimed at further exploring the molecular mechanisms underlying ciliary organization and establishing the contribution of cilia-cilia contact for regulating sensory neuron functions.