Worm Breeder's Gazette 14(1): 96 (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.

A mutation in the beta laminin gene appears to influence degenerin-induced cell death

Gautam Kao1, Monica Driscoll2, Bill Wadsworth1

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).