Embryonic elongation of C. elegans involves cooperation of the epidermal cytoskeleton, muscle tissue, and the extracellular matrix. In screens for elongation-defective mutants we identified
pxn-2, a member of the peroxidasin family of extracellular matrix peroxidases (Ref. 1). Null alleles of
pxn-2 cause 100% lethality at embryonic or early larval stages. PXN-2 is also required postembryonically for maintenance of basement membrane integrity. Peroxidasins are extracellular peroxidases thought to catalyze cross-linking of as-yet unknown substrates in the basement membrane. To identify genes that interact with
pxn-2 we have analyzed a spontaneous extragenic
pxn-2 suppressor,
ju958. In parallel, we are examining basement membrane proteins as candidate substrates for PXN-2-dependent crosslinking. The
ju958 suppressor arose spontaneously during passage of a
pxn-2(
ju358) stock.
ju358 is a viable partial loss of function allele of
pxn-2.
ju958 behaves as a recessive autosomal suppressor. We find that
ju958 can suppress
pxn-2(
tm3464) null mutants to partial (45%) viability, suggesting
ju958 partially bypasses the requirement for PXN-2. We used SNP mapping to localize
ju958 to a 1.3 Mb region on chromosome I. Whole genome sequencing of
ju958 strains (kindly performed by Alex Boyanov and Oliver Hobert) revealed a single missense change in this region, affecting the
vab-10 locus.
vab-10 encodes large cytoskeletal cross-linking proteins known as spectraplakins (Ref. 2). The
vab-10 mutation in suppressed
ju958 strains causes a D to N change in a linker region between the spectrin repeats, common to all
vab-10 isoforms. The affected residue is conserved in other nematodes and Drosophila but not in mammals. Preliminary analysis suggests that
vab-10(
ju958) does not cause elongation defects in a
pxn-2(+) background. We are currently testing whether
vab-10(
ju958) can suppress other elongation-defective mutants. As
vab-10 is itself essential for epidermal elongation it is unclear why a mutation in
vab-10 should suppress the elongation defect in
pxn-2 mutants. Basement membrane function is important for transduction of muscle contractions essential for elongation (Ref. 3).
vab-10(
ju958) may cause an altered function of
vab-10 that allows epidermal cell shape changes to occur despite reduced muscle tension.
1. Gotenstein JR, et al. (2010) Development. 137, 3603-3613.
2. Bosher JM, et al. (2003) J Cell Biol. 161, 757-68.
3. Zhang H, et al. (2011) Nature. 471, 99-103.