The cilia of C. elegans'' amphid channel neurons can be divided into a middle and distal segment. Anterograde intraflagellar transport (IFT) in these cilia is mediated by two kinesin-2 complexes, kinesin II and OSM-3. In the middle segment OSM-3 and kinesin II move together at a speed of 0.7 mm/s, and in the distal segments OSM-3 moves alone at 1.2 mm/s. In the absence of
osm-3 kinesin II moves alone at 0.5 mm/s. The architecture of C. elegans'' cilia suggests that cilia length and function can be dynamically regulated. To investigate whether sensory signals can modulate cilia or IFT we examined the cilia of
gpa-3 mutant animals. GPA3 is a sensory Ga protein that is expressed in all amphid neurons and involved in various sensory processes. Loss of
gpa-3 (lf) does not affect cilia morphology, while a dominant active (gpa-3QL) mutation results in shortened cilia. In addition, we examined animals exposed to dauer pheromone, since previous studies have shown that dauer formation changes in the morphology of some cilia. Furthermore, mutations of
gpa-3 affect dauer formation. We found that in both
gpa-3 (lf) and gpa-3QL mutants, as well as in animals exposed to dauer pheromone, kinesin II and OSM-3 are at least partially uncoupled, while structural IFT particle proteins move at speeds intermediate to the two kinesins. This suggests that the cilia of
gpa-3 mutant animals contain two, possibly three, types of IFT particles: particles transported by OSM-3 or kinesin II alone, and perhaps a small subset transported by both kinesins. We propose a model in which GPA-3 regulated docking of either kinesin II, OSM-3 or both, determines entry of IFT particles into the cilia subdomains. This mechanism would allow plasticity of cilia structure and function. We performed a genetic screen for suppressors of gpa-3QL and identified
sql-1, which encodes the homologue of the mammalian Golgi protein GMAP-210.
sql-1(lf) suppresses the effect of gpa-3QL on cilia length, but does not seem to affect cilia morphology by itself. Speed measurements showed that in the middle segment of
sql-1(lf) animals OSM-3 moves faster (0,85 mm/s) and kinesin II moves slower (0,6 mm/s), suggesting that the two kinesins are at least partially uncoupled. However, both complex A and B proteins move at the same speed as OSM-3. This suggests that in
sql-1(lf) animals IFT is predominantly mediated by OSM-3 kinesin.