Worm Breeder's Gazette 14(4): 71 (October 1, 1996)
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.
| 1 | NYU School of Medicine, 550 First Avenue,, New York, NY 10016 |
| 2 | Rutgers University, Center for Advanced Biotechnology, and Medicine, Piscataway NJ 08854 |
unc-8 is a member of the degenerin/ENaC superfamily of ion channel proteins that acts in motor neurons (Shreffler, et al. 1995; Tavernarakis, et al. submitted). Characterized members of this gene family in mammals function in regulation of blood volume through epithelial Na+ reabsorption. And well characterized family members in C. elegans, including mec-4 and mec-10 function in mechanotransduction. These divergent functions may share a common mechanism -- the perception of membrane stretch. unc-8 may also function as a stretch receptor in motor neurons to maintain normal sinusoidal motion as unc-8 null mutants have a previously unappreciated phenotype of reduced path wave amplitude (Tavernarakis, et al. submitted; see also abstract by Tavernarakis et al.). Such a role in stretch sensitivity has also been recently suggested for a muscle-specific member of this gene family, unc-105 (Liu, et al. 1996).
Eve Wolinsky's lab initiated a large suppressor screen of unc-8 dominant mutants in order to identify other potential channel constituents or regulators. One suppressor locus identified was sup-40 LGI (Shreffler, et al. 1995). Two alleles of sup-40 have been identified, both are dominant suppressors of unc-8(d) and both confer recessive sterility due to an apparent defect in osmoregulation of oocytes. In addition, homozygous sup-40 mutants have a swollen hypodermis and are highly resistant to lethality from exposure to the lipoxygenase inhibitor, NDG (Shreffler, et al. 1995).
sup-40(lb130) has now been shown to also be a suppressor of mec-4(u231)-induced vacuolation. Approximately 50% of lb130; u231 double mutant L1's exhibit no vacuolated cells, while the remainder typically contain one or two dying PLMs or ALMs (u231 alone exhibit multiple cell deaths in nearly 100% of L1's). In addition, the mechanism of suppression appears to be post-transcriptional as inferred from the following experiment. sup-40(lb130) strains were constructed with two integrated mec-4 reporter constructs: one containing only the mec-4 promoter fused to GFP (pmec-4GFP) the other containing the nearly full-length protein upstream of lacZ (mec-4::lacZ). lb130 has no effect on the expression of pmec-4GFP. However, expression of mec-4::lacZ is substantially reduced by lb130. mec-6(u450) affects the expression of these constructs in a similar manner (Gong and Driscoll, 1994). sup-40 may encode a channel subunit that is needed to prevent rapid turnover of UNC-8 and MEC-4 or perhaps it plays a direct role in protein trafficking or processing. It is interesting to note that dominant mutations in human ENaCs map to a motif that is responsible for normal cellular trafficking (Snyder, et al. 1995).
sup-40 was originally mapped to the right of dpy-5
on LGI. Three factor crosses have now placed it to the left of
unc-87 and dpy-14. Mapping with respect to rearrangements
in the region is underway. hDf8 and sDf16 both complement
the recessive sterility of lb130 and hDp72 appears
to cover this locus. ORF's with homology to the deg/ENaC gene
family have not been reported in this region, which is almost
completely sequenced. Experiments to rescue the sterility of lb130
with cosmid DNAs from this region are in progress.
References:
Gong, L., Driscoll, M. Worm Breeder's Gazette 13(2): 72 (1994).
Liu, J., Schrank, B., Waterston, R.H. Science 273: 361-364 (1996).
Shreffler, W, Margardino, T., Shekdar K, Wolinsky, E. Genetics 139: 1261-1272 (1995).
Snyder, P.M., Price, M.P., McDonald, F.J., et al. Cell 83:969-978 (1995).
Tavernarakis, N., Shreffler, W., Wang, S., Driscoll, M. submitted.