Worm Breeder's Gazette 14(5): 42 (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 I

Dewey Royal, Mary Anne Royal , Monica Driscoll

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

     mec-4 encodes a candidate subunit of a mechanosensitive ion channel
that plays a key role in touch transduction. Unusual dominant mec-4(d)
alleles cause the swelling and necrotic-like death of the six touch
receptor neurons. Neurodegeneration is thought to be initiated by
elevated ion influx allowed by the mutant MEC-4 channel. A time course
study of mec-4(d)-inducedneurodegeneration revealed that remarkable
infoldings of the plasma membrane occurs, membranous whorls are
internalized, vacuoles appear and the chromatin clumps (Hall et al.,
     To learn more about mechanosensory ion channel function and about
mechanisms of degenerative cell death, we are isolating suppressor
mutations that block mec-4(d) mediated neurodegeneration. The
mutagenesis scheme involves the expression of the green fluorescent
protein in the touch receptor neurons under the control of the mec-4
promoter. ZB134, a strain in which a pmec-4GFP construct is integrated
into a mec-4(+) background, exhibits 6 brightly fluorescent touch
receptor neurons. When a mec-4(d) allele, mec-4(u231), is crossed into
this background (strain ZB137), fluorescent touch cells are no longer
evident as they have undergone cell death. We mutagenize strain ZB137
and screen for rare animals that have glowing touch cells and thus bear
candidate suppressor mutations. 
     To date we have mutagenized and screened 12,000 haploid genomes for
death suppressing mutations. Our preliminary screen has resulted in
seventeen non-mec-4 alleles that suppress touch cell death.
Surprisingly, many of these exert dominant effects. Mapping and
determination of linkage groups of the suppressors is underway. We are
also testing the three recessive suppressors to determine whether they
fall into distinct complementation groups. The recessive suppressors are
being tested for complementation with mec-6 (mec-6 is the only known
suppressor of mec-4(d)-induced degeneration) and a combinatorial matrix
is being constructed to determine which alleles, if any, possess
discernible epistatic or synergistic effects. We will also determine the
touch sensitivity of the suppressor alleles in the absence of mec-4(d). 
     We are further testing the suppressors for the ability to block the
formation of vacuoles induced by expression of human Ab4 peptide (we
thank C. Link for providing this strain) in order to help distinguish
between general necrotic-like death disrupters and mec-4 channel
disrupters. We are optimistic that our suppressors will identify new
genes that affect channel function, cellular osmotic balance and
necrotic-like cell death.