Cilia are microtubule-based organelles that can be found on the surface of almost all eukaryotic cells. They are assembled and maintained by intraflagellar transport (IFT), which uses microtubule-dependent motor proteins to move IFT particles bi-directionally along the axoneme of the cilium. We study this process in C. elegans. The cilia of C. elegans. amphid channel neurons can be divided into a middle and distal segment. Anterograde 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 .m/s, and in the distal segments OSM-3 moves alone at 1.2 .m/s. In the absence of
osm-3 kinesin II moves alone at 0.5 .m/s. We recently showed that the sensory G. protein GPA-3 plays a role in regulating IFT, and that a dominant active mutant of
gpa-3 (gpa-3QL) affect cilia morphology, resulting in a dye filling defect (see abstract Suzanne Rademakers). To identify new genes in the same pathway we performed a genetic screen for mutants that suppress the gpa-3QL Dyf phenotype. In this screen we found
sql-1 (suppressor of gpa-3QL), which encodes the homologue of the mammalian Golgi protein GMAP-210. Loss of
sql-1 does not affect cilia length, but does partially suppress the effect of gpa-3QL on cilia length. Speed measurements showed that in the middle segment of
sql-1(lf) animals OSM-3 moves faster (0.85 .m/s) and kinesin II moves slower (0.6 .m/s), suggesting that the two kinesins are at least partially uncoupled. Interestingly, IFT complex proteins move at the same speed as OSM-3. This suggests that in
sql-1(lf) animals IFT is predominantly mediated by OSM-3. We are currently investigating how
gpa-3 and
sql-1 interact in the regulation of IFT. Our preliminary results suggest that in the middle segment the
sql-1 mutation is epistatic to
gpa-3(lf) and gpa-3QL, which is in line with the suppression of gpa-3QL. Surprisingly, in the distal segment of gpa-3QL;
sql-1 double mutants OSM-3::GFP speed is significantly reduced.