The dendritic ends of most C. elegans sensory neurons terminate with primary cilia, microtubule-based structures critical for the sensory functions of these cells. Though primary cilia occur in various cell types in animals, little is known about specific tubulins that determine their characteristic architecture and function. We carried out a microarray-based screen for genes expressed in male tail sensory rays, each of which contains two ciliated neurons. This approach identified the beta-tubulin
tbb-4, one of six beta-tubulins in the C. elegans genome. Other bioinformatics approaches have suggested two potential alpha-tubulin partners,
tba-6 and
tba-9. To study the expression of these tubulins, we have created and analyzed transcriptional and translational YFP fusions. A
tbb-4 transcriptional fusion is expressed in ciliated neurons, including amphid, phasmid and labial neurons in both sexes, and ray neurons in males. The TBB-4 translational fusion is specifically localized to the tips of dendrites in these neurons, indicating that TBB-4 is likely to be a component of ciliary microtubules. The
tba-6 transcriptional fusion is expressed in labial neurons and bodywall muscles in both sexes, the HSN, and male tail rays. We are currently constructing translational YFP fusions with
tba-6 and
tba-9. To determine the role of these tubulins in vivo, we have created single and double mutant combinations of
tbb-4(
ok1461) and
tba-6(cxTi4018) in a background containing OSM-6::GFP. Single
tbb-4 and
tba-6 mutations do not disrupt OSM-6::GFP localization along cilia, nor does the double mutant. We are currently using RNAi to reduce expression of
tba-9 in these genetic backgrounds. The
tbb-4 promoter contains a putative X-box, suggesting that it could be directly regulated by the RFX transcription factor DAF-19. A recognizable X-box does not appear in the promoter of either
tba-6 or
tba-9. To determine if the X-box is necessary to drive expression of
tbb-4 in ciliated neurons, we constructed a
tbb-4promoter::YFP fusion in which the X-box was deleted. Preliminary observations suggest that the X-box is required for high levels of
tbb-4 expression. In addition, to determine if DAF-19 is required for
tbb-4 expression, we plan to analyze the expression of our tubulin promoter::YFP constructs in a
daf-19 mutant