mec-4 encodes a subunit of a touch receptor ion channel that is normally needed for mechanosensation. Dominant
mec-4 alleles induce swelling and degeneration of the touch cells via a mechanism proposed to involve increased ion import through this channel. Touch receptor degeneration is accompanied by an unusual sequence of subcellular events that includes striking apparent internalization of plasma membrane-like structures and unusual intracellular trafficking/degradative processes. We are interested in identifying genes involved in the degenerative process and in genes needed for function of members of the degenerin family. We have previously reported that ectopic expression of
mec-4(d) allele can induce degeneration in several cell types. For example, we have found that expression of
mec-4(d) from the
unc-8 promoter the toxic causes swelling and degeneration of some interneurons and many ventral cord neurons, resulting in severe paralysis. We are using this behavioral phenotype to identify suppressor mutations that block the deleterious effects of
mec-4(d)--suppressors restore normal or near normal locomotion by preventing cell death. We have constructed a strain that harbors an integrated array of
punc-8mec-4(d) on chromosome II. These animals are severely paralyzed and exhibit swollen neurons in the nerve ring and in the ventral cord. We have crossed
mec-6(
u450) into the background of this array to verify that the deleterious effects of ectopically expressed
mec-4(d) can be suppressed by a known suppressor mutation. We have mutagenized 20,000 haploid genomes with EMS and identified 16 independent candidate suppressor strains. All proved to retain the integrated
punc-8mec-4(d) array. Of these, 7 appear to be new
mec-6 alleles. Nine alleles complement
mec-6 both for touch insensitivity and death-suppressing defects, thus they may identify previously unknown means of genetically blocking degenerative cell death. Seven of these suppressor alleles have phenotypes independent of the toxic array (either weak Unc or Mec), two alleles do not have an obvious phenotype independent of death suppression. We are currently testing the new alleles to determine if they can suppress death of the touch receptor neurons as assayed in the Is[pmec-4GFP]
mec-4(d) background (described by Royal et al., this issue). Thus far, one of the suppressor alleles has been shown to also block
mec-4(d)-induced neurodegeneration. We are currently focusing on assigning the novel death-suppressor alleles to linkage groups. Encouraged by the success of this pilot mutagenesis we plan to mutagenize more extensively in the hope of identifying all non-lethal loss-of-function mutations that exhibit death suppressing mutations.