Worm Breeder's Gazette 14(5): 43 (February 1, 1997)

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.

Death Defying Acts II

Keli Xu, Nektarios Tavernarakis , Monica Driscoll

Department of Molecular Biology and Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway NJ 08854

     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

     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