Worm Breeder's Gazette 14(1): 44 (October 1, 1995)

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.

Genes Controlling Ion Permeability in C. elegans

Wayne Shreffler, Eve Wolinsky

Dept. Biochemistry, NYU Medical School, 550 First Ave., New York, NY 10016

        Genetic data suggest that unc-8 IV encodes a subunit of a Na+
channel homologous to the passive leak Na+ channels subserving
transepithelial salt and water transport in mammals.  Physiological,
biochemical, and genetic experiments indicate that the ion channel is a
multi-subunit structure, of which two mammalian components have been
molecularly identified: ENaC's and CFTR (Stutts et. al., Science
269:847).  To identify other genes encoding proteins with important
roles in ion channel function, extragenic unc-8 suppressor and enhancer
mutations were sought.  Two unc-8 suppressor loci, sup-40 I and sup-41
IV were described previously (Shreffler et. al. Genetics 139:1261).  We
describe here gene interactions of  two new unc-8 supressor loci,
sup-42(lb88) X and sup-43(lb141) II, and an enhancer locus,
enu-2(lb140).  Sup-43(lb141) is an unusual allele specific suppressor of
unc-8(e49).  Single mutants of either sup-43(lb141) or unc-8(e49)
express a coiler Unc phenotype, while the double mutant
sup-43(lb141);unc-8(e49) behaves as wild-type.
        These three mutations were initially isolated by the sole
criterion of amelioration or exacerbation of  unc-8 locomotion defects,
however, each displays unselected cell swelling phenotypes which further
suggest an effect on membrane permeability:  sup-42(lb88) causes
swelling of embryonic cells, while sup-43(lb141) and  enu-2(lb140) cause
vacuoles within body wall muscle, similar in appearance to those caused
by unc-105(n490).  Waterston et. al. have shown that unc-105 is a member
of the ENaC gene family.  The phenotypic similarities between
sup-43(lb141), enu-2(lb140) and unc-105(n490) are underscored by the
observation that each exhibits striking synthetic lethality in
combination with a fourth mutation, ndg-4(lb108).  Ndg-4(lb108) confers
strong resistance to nordihydroguairetic acid (NDG), a non-specific
lipoxygenase inhibitor; dominant unc-8 mutations are moderately NDG
resistant.  Strikingly, many unc-105(n490);ndg-4(lb108) mutant embryos
are severely vacuolated, while embryonic vacuoles are not observed in
either single mutant.  While the biochemical basis of ndg-4(lb108) drug
resistance is not yet understood, interactions between ndg-4(lb108) and
mutations in three different genes causing vacuoles within body wall
muscle strongly suggest some commonality of action.  Interactions with
ndg-4 are particularly intriguing in the light of reports of effects of
lipo- and epoxygenase inhibitors on CFTR (e.g., Kersting et. al. PNAS
90:4047).  We speculate that unc-8 suppressor mutations may act by
up-regulating an endogenous eicosanoid inhibitor of ENaC activity.  We
are currently analysing a novel unc-8 suppressor strain which expresses
a pale egg phenotype identical to that of ndg-4.  The gene expression
patterns inferred from single and double mutant phenotypes in this and
previous work suggest that overlapping sets of gene products are
available for construction of  Na+ leak channels in motorneurons, and
body wall muscle, and early development.  Phenotypic effects are exerted
in motorneurons by unc-8(dom.), sup-40-43, and mec-6(l-o-f), in body
wall muscle by unc-8(dom. or null), sup-43(lb141), enu-2(lb140),
unc-105(n490), and ndg-4(lb108), and in developing eggs or embryos by
sup-40(lb130), sup-42(lb88), sup-43(lb141), enu-2(lb140), unc-105(n490),
and ndg-4(lb108).