Worm Breeder's Gazette 10(2): 44
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.
Using mutator strains such as RW7097, several dauer-constitutive genes have been tagged with the Tc1 element. The cloning and initial molecular analysis of daf-1 was reported in the last issue (Georgi and Riddle, WBG 10:32, 1987). In an effort to tag certain dauer-defective genes, we have used two positive selections for new mutants. The first selection takes advantage of the fact that most dauer-defective mutants do not respond to the dauer-inducing pheromone (Golden and Riddle, Proc. Nat. Acad. Sci. 81: 819-823, 1984). Addition of exogenous, partially purified pheromone to a synchronously growing culture of L1 larvae can induce all the normal worms to arrest development at the dauer stage, whereas mutants that fail to respond to the pheromone grow to maturity. Using this selection, 23 independent dauer-defective mutants have been isolated. To our shock and horror, all but three of these are also defective in chemotaxis to Na+, as determined by orientation assays. (We have not yet looked at FITC uptake by amphids.) This is a higher proportion of pleiotropic sensory mutants than was obtained by brute-force screening of F2 clones after EMS mutagenesis of N2. Only about half the mutants obtained in the latter screen were chemotaxis-defective. Hence, we can recommend the pheromone selection to those interested in chemosensory mutants. The second selection involves reversion of a temperature-sensitive dauer-constitutive mutant. Thus far, one of the spontaneous revertants of a daf::Tc1 mutant has been found to retain the daf-1 mutation, and also carry an epistatic dauer-defective mutation ( defining a later step in the genetic pathway). This mutant is normal in chemotaxis as are all other dauer-defectives that are epistatic to daf-1. Since our goal is to clone a dauer-defective gene that acts late in the pathway, our analysis will concentrate on the mutants that are normal in chemotaxis. As a byproduct, we seem to have assembled a collection of spontaneous mutants that are presumably affected in amphid development and function, by analogy with similar mutants that we have studied in the past (Albert, Brown and Riddle, J. Comp. Neurol. 198: 435-451, 1981).