Dauer larva formation in C. elegans requires chemosensation of a dauer pheromone. Mutations in genes required for the dauer pheromone response cause either a dauer defective (Daf-d) or a dauer constitutive (Daf-c) phenotype. By epistasis analysis, these genes have been ordered into a negative regulatory pathway of gene action (Vowels and Thomas, 1992; Riddle, et al., 1981). In double mutants between the Daf-c gene,
daf-11 ,and a set of dauer defective mutants with structurally abnormal chemosensory cilia (e.g.
osm-1 ,
osm-3 ,
che-11 ,
che-13 ,
daf-6 and
daf-10 ,Perkins, et al., 1986, Albert, et al, 1981), the Daf-c phenotype of
daf-11 is suppressed (see Table 1 and Vowels and Thomas, 1992). These results suggest that
daf-11 is acting upstream of this class of chemosensory cilium mutants, and requires wild type chemosensory cilia for proper signal transduction. Therefore,
daf-11 is a good candidate for one of the proximal signal transduction components in the pheromone sensing pathway. The
unc-104 gene encodes a protein with homology to heavy chain kinesins, and appears to be involved in organelle transport (Otsuka, et al., 1991; Hall and Hedgecock, 1991). We have found that the partial loss-of-function
unc-104 (
e1265)mutant responds more weakly to dauer pheromone than the wild type, and makes fewer dauers than normal on starved plates. To test for possible interactions among
unc-104 ,
daf-11 ,and the cilium structure mutants
osm-1 and
osm-3 ,we constructed several double and triple mutant strains and tested for constitutive dauer formation at 25 C (Table 1). [See Figure 1] Two surprising results were observed. First, although an
osm-1 (
p808 )mutant is dauer defective, and an
unc-104 (
e1265)mutant is partially dauer defective, the double mutant between them is dauer constitutive. Double mutants between
unc-104 (
e1265)and other alleles of
osm-1 give similar results. In addition, we have constructed double mutants between
unc-104 (
e1265)and other mutations that affect amphid structure; the
che-13 (
e1124)and
che-11 (
e1810)double mutants show a low level of dauer constitutivity (<15%), while the
daf-6 (
e1377)and
daf-10 (
e1387)double mutants show no dauer constitutivity. Finally, this result is not dependent on the
unc-104 allele used, as
unc-104 (
rh1017);
osm-1 (
p808 )double mutants are slightly dauer constitutive. A formal interpretation of these results is that
unc-104 and
osm-1 encode functionally redundant proteins that are required to repress dauer formation in the absence of inducing conditions. The second surprising result is that although
daf-11 with
osm-3 or
osm-1 makes almost no dauers, and
unc-104 also makes no dauers under non-inducing conditions, the
daf-11 ;
unc-104 triple mutants with
osm-3 and
osm-1 are strongly dauer constitutive. This result suggests that in the absence of
unc-104 function, the
daf-11 mutant phenotype no longer requires wild type sensory cilia.