Worm Breeder's Gazette 12(3): 95 (June 15, 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.
Cold-sensitive (cs) mutations in C. elegans have been classified as having phenotypes that are stronger at 15°C than at 25°C. Extragenic suppressors to cs mutations may have an independent temperature (heat) -sensitive (ts) phenotype in the absence of the original mutation. This type of genetic analysis has been used to identify interacting genes in phage and yeast (Botstein). we are interested in isolating cs mutants for use in a suppressor analysis of genes important for development and neuromuscular function in C. elegans.
Ts mutations in C. elegans were isolated at the stringent temperature of 25°C, where the progeny produced per hermaphrodite falls from ~300 to ~100 (Hirsh). An analogous restrictive condition for the isolation of cs mutants was required. We found that at ~11°C fecundity was compromised to the same extent observed at 25°C and development was slowed by a factor of two as compared with that at 16°C. This more stringent temperature was used to screen for cs mutations that affect movement and development in the nematode.
Mutagenized and synchronized populations of nematodes were enriched for slow-moving and unc phenotypes by using a gradient of bacteria as a chemoattractant. The screen consisted of 167 independent 'race track' experiments which represented an excess of one million ethylmethane sulfonate (EMS) mutagenized gametes. Out of 3182 slow-moving individuals, 14 independent isolates were found to be true cold-sensitives, i.e., they behaved in an uncoordinated fashion at 11°C but moved normally at permissive temperature ( ~23°C ) . Nine of the 14 cs unc mutants that expressed the 'kinker' phenotype mapped to the X chromosome. Based on initial two-factor crosses and complementation tests, they appear to represent a minimum of three different loci.
A recent screen for mutants that arrest development at 11°C yielded more than twenty independent cs lethal mutations from 1740 EMS mutagenized F2 individuals. The phenotypic distribution of these cs lethals appears to be similar to that previously reported for ts lethals, though they appear to be half as frequent.
To ultimately identify and characterize interacting genes that affect development and neuro-muscular function, we will isolate extragenic suppressors to these cs mutations and test whether they gain an independent ts phenotype.