Worm Breeder's Gazette 12(4): 59 (October 1, 1992)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
C. elegans can form an alternative developmental stage called the dauer larva when exposed to high levels of dauer-inducing pheromone. Many genes have been identified that are involved in the formation of a dauer. Mutations in most of these genes are either dauer constitutive (Daf-c) or dauer defective (Daf-d). The genes have been placed in a regulatory pathway based on gene interactions (see Thomas and Birnby, this issue). Although Daf-d mutations in the part of the pathway downstream of daf-7 have been screened for intensively, screens that might identify Daf-d genes just downstream of daf-11 have been very limited. Nearly all such mutations have been discovered fortuitously in other screens.
To identify Daf-d genes that lie just downstream of daf-11 ,we screened for EMS-induced suppressors of the Daf-c phenotype of daf-11 ( m87 ).The screen identified 47 independent mutations. Of these, 16 conferred an FITC-filling and osmoticavoidance defect, indicating that they probably affected amphid and phasmid cilium structure. These were sent to C. Kari and R. Herman, who have shown that they include 3 osm-1 mutations, 2 osm-3 mutations, 2 osm-5 mutations, 1 osm-6 mutation, and 1 che-2 mutation. The remaining 31 mutants were normal for either FITC-filling or osmotic-avoidance or both. Tentative double mutants between daf7 ( e1372 )and these 31 suppressor mutations were constructed in an attempt to determine where in the pathway the new mutations act. Only one mutation could suppress the Daf-c phenotype of daf-7 ,and it proved to be a new allele of daf-12 .This result suggests that the remaining 30 mutations may affect previously unidentified genes involved in the dauer formation pathway.
The remaining 30 suppressor isolates have been tested for response to dauer pheromone. Response was assessed by setting synchronous egg lays (approximately 50-150 eggs) on pheromone-containing plates and M9 -controlplates. The plates were placed at 25° C and scored 55 hours later for the percentage of dauer formation. Nineteen of the mutants were pheromone non-responsive under our assay conditions, one was responsive, and the remaining ten gave inconclusive results.
Many of these 30 suppressor mutants have been mapped to a chromosome, and a few have been placed into complementation groups. Sixteen of the mutants have been tentatively mapped to chromosomes using 2-factor crosses. Five appear to map to chromosome I, one to chromosome II, six to chromosome V, and four to the X chromosome. Limited complementation tests have been performed for the mutations that are located on chromosomes I and V. There appear to be at least two complementation groups on chromosome I and at least 3 complementation groups on chromosome V.
One of the 30 mutations, sa177 ,is dominant for its suppressor activity. This mutation appears to be closely linked to daf-11 . The suppressor isolate is pheromone responsive, and unlike daf-11 ( m87 ),has a normal response to odorants. Therefore, sa177 appears to be G strong candidate for an intragenic revertant of daf-11 ( m87 ).