Based on the details explained below, several of the phenotypes previously attributed to
flp-1 mutants are more likely to be caused by loss of
daf-10 . These include defects in osmotic avoidance (Osm), thermal avoidance (Tav), nose-touch response (Not), wandering behavior, regulation of dauer formation, and possibly regulation of egg-laying behavior in response to food signals. Defects in these behaviors are characteristic of cilium-structure mutants, and could be easily accounted for by loss of
daf-10 . In surveying a variety of behavioral mutants for a dauer phenotype at 27deg, we found that both
flp-1 deletion mutants,
yn2 and
yn4 , have a moderate Daf-c phenotype at 27deg and poor dauer recovery. Since many 27deg Daf-c mutants are hypersensitive to dauer pheromone, we tested
flp-1(
yn2) for response to pheromone at 25deg. Surprisingly, it formed no dauers in response to pheromone. Mutations in the dyf genes similarly lead to a Daf-d phenotype at 25deg and a Daf-c phenotype at 27deg. These mutants have defects in the structure of the ciliated endings of sensory neurons, a defect which can be assayed by the failure of these neurons to fill with fluorescent dyes. Thus, we performed FITC dye-filling assays on
flp-1(
yn2 ) and
flp-1(
yn4) and found that both mutants failed to exhibit dye-filling of any of the amphid or phasmid neurons.
flp-1 is not expressed in any of the amphid sensory neurons. Thus, we suspected that the
flp-1 Dyf phenotype was due to a background mutation present in both
flp-1 strains. The two alleles are not independent since they were isolated as deletions from the same parent strain which carries a Tc1 insertion just upstream of
flp-1 . We mapped the Dyf phenotype and found that it mapped to the right of
unc-5 and was not separable from
flp-1 (based on
flp-1 movement phenotypes). The only candidate dyf mutant in this region is
daf-10 . We found that
flp-1(
yn2) failed to complement
daf-10(
e1387) for the Dyf phenotype, indicating that the
flp-1 mutant strain also carries a mutation in
daf-10 . The
flp-1 strains exhibit a more severe dye-filling defect than
daf-10(
e1387) , indicating that they are stronger alleles.
daf-10 is encoded by F23B2.4 (Steve Stone and Jocelyn Shaw, personal communication), the gene immediately upstream of
flp-1 . Further inspection of the
flp-1 deletions indicates that
yn2 and
yn4 both delete the
daf-10 promoter and from two to four exons of the predicted
daf-10 coding sequence. The original Tc1 used to isolate the
flp-1 deletions appears to reside in the
daf-10 gene, and both
flp-1 deletion alleles are likely null for both genes. Although several of the sensory phenotypes of
flp-1 mutants can be explained by loss of
daf-10 , it is likely that several other phenotypes previously ascribed to
flp-1 are bona fide
flp-1 phenotypes. Specifically,
flp-1 mutants have defects in movement and regulation of the active state of egg-laying that are not easily explained by loss of
daf-10 . Furthermore, both of these phenotypes were rescued by
flp-1(+) transgenes.