Worm Breeder's Gazette 15(1): 54 (October 1, 1997)
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 Medical Genetics, University of British Columbia, Vancouver, BC V6T 1Z3
bli-4 was originally identified by a single viable allele,
e937, which results in blistering of the adult cuticle. Our
laboratory has since shown that bli-4 is an essential gene that
encodes at least four serine endoproteinases that belong to the
kex2/subtilisin-like (kexin) family of proprotein convertases (1).
e937 is a 3250 bp deletion that results in loss of expression of one
bli-4 isoform called blisterase A.
In order to understand the role of bli-4 we have been trying
to identify genes that may encode potential substrates. Candidates
include several Dpy genes that are suppressors of blistering. dpy-5
is a dominant suppressor of the blistered allele e937 (2),
suggesting that DPY-5 may be a substrate for BLI-4. Heidi Browning
in Susan Strome's laboratory has been able to rescue dpy-5 using the
cosmid B0342 (3). Thanks to data generated by the genome sequencing
consortium we were able to examine the corresponding genomic
sequence for predicted gene products that contain the Arg-X-X-Arg
cleavage motif that is recognized by members of the kexin family.
One candidate, F27C1.8, encodes a cuticle collagen composed of 284
amino acids. We sequenced the F27C1.8 coding region from three dpy-5
mutant strains including e61 and two alleles isolated in Dave
Baillie's laboratory, and found lesions for all three mutants. The
e61 and s102 mutations are lesions at the same nucleotide in which a
glycine codon (Gly202) of a typical collagen Gly-X-Y motif is
changed to an opal stop codon, which would lead to the loss of 81
carboxy-terminal amino acids. The nonsense mutation is consistent
with the demonstration by Hodgkin and colleagues that e61 is smg-
suppressible (4). The allele s111 is the result of a 54 bp deletion
within the run of Gly-X-Y motifs yet leaves the protein in-frame.
Interestingly, s111 homozygotes are not as severely Dpy as other
dpy-5 mutants examined, suggesting that the truncated protein is not
as disruptive to the normal morphology of the animal as compared to
other dpy-5 mutations. The 32P induced mutation e907 is a deletion
that completely removes the cuticle collagen gene and flanking
sequences. The most severe Dpy-5 phenotype is caused by e565:
homozygotes are slow growing and smaller than all other dpy-5 mutant
animals. Although we have not fully characterized e565, it appears
that the molecular lesion is an intragenic insertion.
Based on the sequencing of the mutations, we have shown that
dpy-5 (F27C1.8) encodes a cuticle collagen. dpy-13 is also a
dominant suppressor of e937 (2), and like dpy-5 encodes a cuticle
collagen which contains the Arg-X-X-Arg cleavage motif (5). These data
are compatible with the proposal that blisterase A processing activity
is required for the production or maintenance of the adult cuticle.
(1). Thacker et al., (1995) Genes Dev. 9: 956-971.
(2). Peters et al., (1991) Genetics 129: 95-102.
(3). Browning et al., (1996) Genetics 144: 609-619
(4). Hodgkin et al., (1989) Genetics 123: 301-313
(5). von Mende et al., (1988) Cell 55: 567-576.