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.

Tagging Dauer-defective Genes

Wen-Hui Yeh and Donald L. Riddle

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).