Embryonic Expression of
unc-8 suppressor
sup-42 Wayne Shreffler and Eve Wolinsky Dept. Biochemistry, NYU Medical School, *0 First Ave., NY 10012 Strong
unc-8 (IV) dominant mutations produce ventral motorneuron swelling, coiling, and inability to back. These phenotypes are suppressed by
mec-6 mutations (WBG13(3):77, Genetics, in press), suggesting afunctional similarity to members of the
deg-1 ion channel family. The strong
unc-8 phenotype allows ready isolation of suppressor mutations that restore the ability to move backwards. One such mutation,
sup-42(
lb88) X, obtained after EMS mutagenesis of
unc-8(
n491), recessively restores backing ability and largely suppresses the motorneuron swelling phenotypes of
unc-8 strong dominant mutations, although it does not restore fully wild-type locomotion. Cultures of
unc-8(
n491);
sup-42(
lb88) double mutants also grow surprisingly slowly despite this amelioration of the Unc-8 phenotype.
sup-42(
lb88) in the absence of other mutations confers an extremely mild sluggish Unc phenotype. The slow growth of the double mutant, may, however, be explained by embryonic lethality of
sup-42(
lb88). 25 percent of
sup-42(
lb88) eggs and 44percent of
unc-8(
n491);sup 42
(lb88) eggs fail to hatch, as compared to 1percent of wild-type strain N2 and 8percent of
unc-8(
n491) single mutant eggs. At least 10percentof both early and late sup 42
(lb88) and
unc-8(
n491);
sup-42(
lb88) embryos contain large swollen cells. These embryonic swellings could be due to an osmotic defect or reflect secondary leakiness of cells dying from other causes. Larval lethality is comparable to wild-type; with the exception of unusual sickly newly-hatched animals, cell swel!ing is not observed in larvae or adults. Thus,
sup-42 appears to function during embryogenesis, as well as interacting with
unc-8 in the nervous system after hatching.
sup-42(
lb88) suppression of
unc-8(
n491) in a
mec-6(+) background argues against functional redundancy with
mec-6.
sup-42 might be a functional homolog of the
deg-1 family, in which case suppression of
sup-42(
lb88) embryonic lethality by
mec-6 is predicted. Interactions of
sup-42 with other
deg-1 family members and
unc-8 suppressor mutations are being tested. Perhaps
sup-42(
lb88) will prove to identify a novel channel regulator. In order to clone
unc-8 and its hypodermally-active suppressor gene sup 40 (I), we have been injecting nearby cosmids. Both genes are identified by dominant mutations with deleterious effects, therefore a multi-copy array of wild type DNA may be harmful. It has proven, in fact, extremely difficult to obtain any transformants (as marked by coinjected antisense Roller plasmid), and no stably transmitting arrays have yet been obtained from either the LGI or LGIV cosmids injected as a group. We are currently trying to identify an individual "killer" cosmid from each group (which may, however, encode a harmful sequence unrelated to
sup-40 or
unc-8).