Worm Breeder's Gazette 16(2): 33
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.
Department of Zoology, University of British Columbia, Vancouver, B.C. Canada
Embryos homozygous for mutations in the unc-52, pat-3 and unc-112 genes
of C. elegans exhibit a similar Pat phenotype. Myosin and actin are not
organized into sarcomeres in the body wall muscle cells of these
mutants, and dense body and M-line components fail to assemble (Williams
and Waterston, 1994, JCB 124:475). The unc-52 (perlecan) and pat-3
(b-integrin) genes encode ECM or transmembrane proteins found at the
cell-matrix adhesion sites of both dense bodies and M-lines. We have
determined that the unc-112 gene encodes a novel, membrane-associated,
intracellular protein that co-localizes with integrin at cell-matrix
adhesion complexes.
The 720 amino acid UNC-112 protein is most similar to a human
protein of unknown function called Mig-2 (Wick et al. 1994, J. Cell
Sci.107:227), and shares a region of homology with talin and other
members of the FERM superfamily of proteins. A functional UNC-112::GFP
protein is expressed in the body-wall muscle of embryos, and in the
body-wall, vulval, spermathecal, uterine, and anal sphincter/depressor
muscle cells of adult hermaphrodites. In body wall muscle, UNC-112::GFP
co-localizes with PAT-3/b-integrin at dense bodies, M-lines and adhesion
plaques.
We have identified the sequence alterations corresponding to the
four known unc-112 alleles. The EMS-induced st562 and st581 mutations
are single nucleotide alterations that introduce stop codons into the
unc-112 coding sequence. The formaldehyde-induced gk1 allele obtained
from the C. elegans Reverse Genetics Core Facility is a 2.18 kb
deletion. Embryos homozygous for these three null mutations exhibit a
Pat terminal phenotype. They arrest at the two-fold stage of
embryogenesis and have severely disorganized body wall muscle. In
contrast, animals carrying the r367 allele of unc-112 are viable,
although they do have disorganized body wall muscle and are paralyzed as
adults. The r367 lesion is a missense mutation in the amino-terminal
region of the protein that results in a Thr to Ile change.
Our analysis of unc-112(st581) mutant embryos using the MH2, MH24
and MH25 mAbs (Francis and Waterston, 1985, JCB 101:1532) has revealed
that UNC-112 is required to spatially organize PAT-3/b-integrin clusters
after they are integrated into the basal cell membrane, but is not
required to organize UNC-52/perlecan in the basement membrane nor for
DEB-1/vinculin to associate with PAT-3/b-integrin. We also have
determined that UNC-112 requires the presence of UNC-52/perlecan and
PAT-3/b-integrin, but not DEB-1/vinculin for its proper localization in
the muscle cell membrane.
In summary, we have identified a new component of cell-matrix
adhesion structures, the ~80 kD UNC-112 protein. We have shown that
UNC-112 co-localizes with PAT-3/b-integrin, and that each of these
proteins is required for the correct distribution of the other in the
muscle cell membrane. We expect that the human ortholog of UNC-112, the
Mig-2 protein, will also be associated with adhesion complexes.