Worm Breeder's Gazette 14(1): 96 (October 1, 1995)
|1||Dept. of Pathology,, Robert Wood Johnson Medical School,, Piscataway NJ 08854|
|2||Rutgers University, Centre for Advanced Biotechnology and Medicine, Piscataway NJ 08854|
We have detected genetic interactions between two degenerins and laminin beta, a major component of the basement membrane (BM) that is characterized by a single non-null allele, lam-1(rh219). Preliminary analysis of this interaction has been reported at the last International C. elegans meeting. The mec-4 and mec-10 degenerin genes encode ion channel subunits related to the mammalian epithelial Na+ channel. MEC-4 and MEC-10 are hypothesized to be components of a mechanosensory ion channel in the touch receptor neurons. The molecular mechanism of action of mechanically gated channels is not understood since few members of this channel class have been cloned. However, biophysical studies in several systems suggest that mechanically-gated channels require that tension be exerted across gating domains to trigger channel opening and closing. Tension-generating associations may involve interaction of channel subunits with the extracellular matrix and with cytoskeletal proteins. Indeed, mec-5 encodes a collagen family member that is needed for touch receptor function that could participate in such an interaction (see Gu and Chalfie WBG 13.4 p85). To ask whether other basement membrane components could influence degenerin function, we constructed a lam-1(rh219); mec-4(u231d) double mutant and scored for vacuolar cell deaths. In a lam-1(+); mec-4(u231) strain, degenerating touch receptor neurons disappear by the L2 stage. In contrast, at a low frequency commensurate with the penetrance of the rh219 mutation, the lam-1(rh219); mec-4(u231d) double mutant adults exhibited swollen cells characteristic of the mec-4(d) defect. Thus, disruption of extracellular matrix interferes with the efficiency of degeneration. We also tested for the influence of lam-1 on mec-4(d)-induced cell death by scoring for the viability of the tail touch receptors in a transgenic lines that harbored an integrated mec-4::GFP fusion gene. This fusion causes the touch receptors to fluoresce in an otherwise wild type background. In a mec-4::gfp; mec-4(u231) strain no fluorescence is observed because the toxic mec-4 protein kills the touch cells before they are competent to express mec-4::gfp. In the presence of rh219, fluorescing cells are seen, indicating that cells have time to express detectable mec-4::gfp before they die. This effect of rh219 is not limited to mec-4(d) since lam-1(rh219); deg-1(u38d) animals show a similar phenotype (deg-1 is another member of the degenerin family that can mutate to induce neurodegeneration). Adult lam-1(rh219); deg-1(u38) double mutants are observed to have swollen cells whereas most swollen cells disappear earlier in u38. Our results suggest that lam-1 is important for efficient degenerin-induced cell death. This may reflect a requirement for the integrity of the basement membrane for channel activity. Alternatively, delayed onset and persistent vacuoles may be required for timely removal of degenerative cell death corpses (see abstract by Chung and Driscoll, this volume).