Mutations in the alpha 2(IV) basement membrane collagen gene of Caenorhabditis elegans produce phenotypes of differing severities.

Abstract

Type IV collagen forms a network that provides the major structural support of basement membranes. We have determined the nucleotide alterations and phenotypes of 17 mutant alleles of the Caenorhabditis elegans alpha 2(IV) collagen gene let‐2. All 17 mutations are within the triple helical (Gly‐X‐Y) repeat domain of the molecule. Fifteen of the mutations are replacements of Gly‐X‐Y repeat glycines with aspartate, glutamate or arginine, and they cause a wide range of phenotypes. The mildest alleles are nearly wild‐type at 15 and 20 degrees C but embryonic lethal at 25 degrees C, while the most severe allele is embryonic lethal at all three temperatures. Mutations resulting in severe phenotypes are generally located in areas of lower calculated thermal stability of the type IV collagen molecule. An alanine to threonine substitution at position X of a Gly‐X‐Y triplet immediately following an interruption results in a severe phenotype. This mutation is unusual because substitutions at positions X or Y have not generally been found to cause strong phenotypes in C. elegans or human collagens. An intron splice acceptor mutation causes a strict embryonic lethal phenotype, but does not completely abolish gene function. Pairs of independent mutations affect each of three glycines, indicating a non‐random distribution of mutations in the molecule. It is suggested that this clustering results because many glycine substitutions may cause dominant lethal or sterile phenotypes.

MIG-17/ADAMTS controls cell migration by recruiting nidogen to the basement membrane in C. elegans

“…1 C, D, and F). let-2 encodes LET-2A and LET-2B, two spliced isoforms of the ␣2 chain of type IV collagen (12). The k193 and k196 mutants contained amino acid substitutions in the NC1 domain and Gly-X-Y repeats of LET-2, respectively [supporting information (SI) Fig.…”

“…Two ts lethal alleles, g25 and b246 (12), suppressed the DTC migration defects very weakly at 20°C (Table S2). When animals were shifted from 20°C to 22.5°C at the L2 stage, b246 and g25 partially suppressed the posterior gonadal defects of mig-17.…”

Basement membranes

“…Most emb-9 and let-2 mutations are missense alterations of Gly residues in the Gly-X-Y repeat domains (Figure 3; Guo et al, 1991;Gupta et al, 1997;Sibley et al, 1994). Such alterations are expected to inhibit folding/stability of the triple-helical structure and have been shown to inhibit secretion of the mutant collagen.…”

“…The major C. elegans basement membrane proteins and their receptors are listed in Tables 1 and 2. Collagen IV α1 emb-9 1 Emb (2-3X) Guo et al, 1991;Gupta et al, 1997 Collagen IV α2 let-2 2 Emb (2-3X) Sibley et al, 1993Sibley et al, , 1994 Collagen XVIII cle-1 4 Neuro, gonad morph Ackley et al, 2001Ackley et al, , 2003 Fibulin-1 fbl-1 2 Gonad morph Hesselson et al, 2004;Kubota et al, 2004 Hemicentin Osteonectin/SPARC ost-1 1 Acc (L1-L2) Fitzgerald and Schwarzbauer, 1998 Papilin ppn-1 3 Emb (hyp enclosure) Kramerova et al, 2000 Perlecan unc-52 >5 Pat Rogalski et al, 1993Rogalski et al, , 1995 In C. elegans, BMs surround all internal tissue surfaces, covering body wall muscles, pharynx, intestine, gonad and the pseudocoelomic face of the hypodermis. The BM covering the ventral and dorsal nerve cords interposes between motor neurons and muscles and forms part of the neuromuscular junctions, as is also the case in vertebrates.…”

The Basement Membrane Components Nidogen and Type XVIII Collagen Regulate Organization of Neuromuscular Junctions inCaenorhabditis elegans

“…Mutations in several C. elegans BM genes have been characterized, including type IV collagen chains emb-9 and let-2 (Guo et al, 1991;Sibley et al, 1994;Gupta et al, 1997), nidogen nid-1 (Kang and Kramer, 2000;Kim and Wadsworth, 2000), perlecan unc-52 (Rogalski et al, 1995), and type XVIII collagen cle-1 . NID-1 and CLE-1 are associated with the nervous system (Kang and Kramer, 2000;Ackley et al, 2001), whereas EMB-9, LET-2, and UNC-52 are not (Sibley et al, 1994;Graham et al, 1997;Mullen et al, 1999).…”