Type XII collagen: distinct extracellular matrix component discovered by cDNA cloning.

Abstract

We have screened a cDNA library constructed from tendon fibroblast mRNA for the presence of collagenous coding sequences. Nucleotide sequence analysis of one isolated clone, pMG377, reveals that the clone encodes a polypeptide that is homologous to, yet distinctly different from, type IX short-chain collagen polypeptides. The structure of the conceptual translation product of the cDNA is also different from that of all other collagen types. Therefore, we The extracellular matrix components classified as collagens on the basis of their triple-helical domain constitute a heterogeneous group of proteins with a variety of molecular structures and interaction properties. Within this group, the fibrillar collagens I, II, III, and V form characteristic "quarter-staggered" fibrils in connective tissues (for a review, see ref. 1). However, types IV, VI, VII, VIII, IX, and X collagens do not form these kinds of fibrils and have molecular structures distinct from those of fibrillar collagens. We have isolated genes encoding the polypeptides of types IX and X collagens, and we have found that the genes for these two "short-chain" collagens also have an exon structure that is clearly distinct from that of fibrillar collagen genes (2, 3).Although the function of type IX collagen in extracellular matrices is not known, some intriguing structural characteristics of this collagen are known. First, the molecules do not contain one long triple-helical domain like fibrillar collagens but instead are composed of three triple-helical domains interspersed with noncollagenous domains (4). Second, type IX collagen contains a sulfated glycosaminoglycan side-chain covalently attached to the polypeptide subunit designated the a2(IX) chain. This gives type IX collagen a proteoglycan character (5-8).cDNA probes corresponding to the al(IX) and a2(IX) chains (9,10) have been used to demonstrate that type IX collagen mRNAs are expressed in a tissue-specific manneri.e., they are expressed by chicken embryo chondrocytes but not by chicken embryo fibroblasts (9, 11). However, tendon fibroblasts do contain mRNAs capable of synthesizing bacterial collagenase-sensitive polypeptides that are similar in size to type IX polypeptides (11). To explore the nature of these polypeptides in detail, we have screened a cDNA library constructed from tendon fibroblast mRNA for the presence of collagenous coding sequences. Here we report on the isolation and characterization of one such clone, pMG377. Nucleotide sequence analysis reveals that the clone encodes a collagenous polypeptide that is homologous to, yet distinctly different from, type IX collagen polypeptides synthesized by chondrocytes. The structure of the conceptual translation product of pMG377 is different from that of collagens I-X and type XI (la, 2a.) chains. Therefore, we have given the type IX-like collagen chain encoded by pMG377 the designation al(XII). Ribonuclease protection assays using cRNA derived from pMG377 as probe show that al(XII) mRNA is present in several tissues, such as...

Bovine type XII collagen: Amino acid sequence of a 10 kDa pepsin fragment from periodontal ligament reveals a high degree of homology with the chicken α1(XII) sequence

“…We report here the purification of a 10 kDa fragment from the bovine periodontal ligament and demonstrate by amino acid sequence analysis that it is highly homologous to the chicken ce~(XII) sequence reported by Gordon et al [3]. Our data provide the first evidence for the presence of type XII collagen in a mammalian tissue and demonstrate for the studied region, a much higher sequence conservation between avian and mammalian trl(XII) chains than between avian and mammalian al(IX) chains.…”

“…Since several collagen genes are coordinately expressed in different tissues, an analogue for type IX collagen in type I collagen containing extracellular matrices has been postulated by some investigators. The first demonstration of the existence of such an analogue came from the description of a cDNA clone (pMG377), isolated from a 17-day-old chick embryo tendon library, by Gordon et al [3]. These authors designated the encoded polypeptide chain as the oe~ chain of type XII collagen.…”

Immunoidentification of type XII collagen in embryonic tissues [published erratum appears in J Cell Biol 1989 Nov;109(5):following 2254]

“…The presence of type XII collagen as protein in embryonic tendons was confirmed by Dublet and van der Rest (3). These investigators isolated pepsin-resistant fragments from embryonic tendons and demonstrated that the amino acid sequence of a tryptic peptide derived from one of these fragments was in agreement with the conceptual translation product predicted from the nucleotide sequence of the type XII cDNA, pMG377 (3,6).…”

“…The presence of type XII collagen as protein in embryonic tendons was confirmed by Dublet and van der Rest (3). These investigators isolated pepsin-resistant fragments from embryonic tendons and demonstrated that the amino acid sequence of a tryptic peptide derived from one of these fragments was in agreement with the conceptual translation product predicted from the nucleotide sequence of the type XII cDNA, pMG377 (3,6).In this article we describe the generation of a monoclonal antibody against a synthetic oligopeptide, whose sequence was derived from the nucleotide sequence of pMG377. This peptide sequence is located within the carboxy-terminal nontriple-helical domain of od(XII) chains, and it was selected because of its low level of similarity with the corresponding domains in otl(IX) and ot2(IX) chains.…”

“…A recent addition to the collagens is type XII collagen which has been discovered by cloning cDNA from chick embryonic tendon mRNA (6). Exhibiting partial similarity to type IX collagen, the sequence of t~l(XII) has prompted the speculation (18) that type XII collagen may be associated with type I collagen containing fibrils as type IX collagen is associated with type II-containing fibrils in cartilage (5,21,22).…”