D-periodic distribution of collagen type IX along cartilage fibrils

Ultrastructural organization of type XI collagen in fetal bovine epiphyseal cartilage

Type XI collagen was localized with polyclonal antibodies specific for alpha 1 (XI) and alpha 2 (XI) chains in the resting zone of epiphyseal cartilage from calf fetuses. The immunofluorescence technique was used on sections of cartilage, and the immunogold labelling technique for electron microscopy on fibrils isolated from cartilage and, for the first time, in situ on blocks of cartilage fractured in liquid nitrogen. Immunofluorescence showed that without pepsin treatment the staining of type XI collagen was restricted to the pericellular zones; after pepsin treatment, the staining was co-distributed with that of type II collagen. Immunoelectron microscopy performed on isolated fibrils and on cartilage blocks showed that after disruption of fibrils with pepsin, type XI collagen was labelled on small filaments on the fibrils. When the fibrils were not disrupted, labelling was observed in situ only at the ends of the fibrils or on cross-sections of some fibrils. These results indicate that type XI collagen is located inside type II collagen fibrils in fetal bovine epiphyseal cartilage, as already postulated for embryonic chicken sterna.

Quantification and immunolocalisation of porcine articular and growth plate cartilage collagens

The collagens of growth plate and articular cartilage from 5–6 month old commercial pigs were characterised. Growth plate cartilage was found to contain less total collagen than articular cartilage as a proportion of the dry weight. Collagen types I, II, VI, IX and XI are present in both growth plate and articular cartilage whereas type X is found exclusively in growth plate cartilage. Types III and V collagen could not be detected in either cartilage. Type I collagen makes up at least 10% of the collagenous component of both cartilages. There are significant differences in the ratios of the quantifiable collagen types between growth plate and articular cartilage. Collagen types I, II, and XI were less readily extracted from growth plate than from articular cartilage following pepsin treatment, although growth plate cartilage contains less of the mature collagen cross-links, hydroxylysyl-pyridinoline and lysyl-pyridinoline. Both cartilages contain significant amounts of the divalent reducible collagen cross-links, hydroxylysyl-ketonorleucine and dehydro-hydroxylysinonorleucine. Immunofluorescent localisation indicated that type I collagen is located predominantly at the surface of articular cartilage but is distributed throughout the matrix in growth plate. Types II and XI are located in the matrix of both cartilages whereas type IX is predominantly pericellular in the calcifying region of articular cartilage and the hypertrophic region of the growth plate. Collagen type VI is located primarily as a diffuse area at the articular surface.

Autoantibodies to cartilage collagens in relapsing polychondritis

Relapsing polychondritis is a systemic disease associated with a destruction of cartilage in various parts of the body. Sera from six patients with relapsing polychondritis and one patient with microscopic polyarteritis nodosa as well as from six controls were analyzed by immunoblotting and ELISA. All patients had autoantibodies against native collagens II and IX. The serum from one patient showed a strong reaction with all three collagen chains of the high molecular weight fraction of collagen IX after denaturation; sera from four patients showed autoantibodies against alpha 2 (XI) and sera from three patients showed autoantibodies against the covalently cross-linked gamma component of collagen XI. The presence of autoantibodies against collagens II, IX, and XI, which form the major fibrillar scaffold in cartilage and mediate the interaction of collagen fibrils and proteoglycan, suggests that autoantibodies against cartilaginous collagen may play a crucial role in the pathogenesis of relapsing polychondritis and microscopic polyarteritis nodosa.

Evidence for the degradation of type XI collagen by bovine intervertebral disc- and articular cartilage extracts

Bovine intervertebral disc- and articular cartilage extracts contain a metalloproteinase system capable of degrading type XI collagen. The collagen-degrading activity is rather low in unmodified extracts but increases considerably on metalloproteinase activation. The similarity between intervertebral disc and articular cartilage in their patterns of (casein-degrading) metalloproteinases and type XI and type II collagen degradation is believed to suggest a similarity in the events underlying the degradative disorders of articular cartilage and intervertebral disc.

Expression of type XIV collagen during the differentiation of fetal bovine skin: immunolabeling with monoclonal antibody is prominent in morphogenetic areas

Type XIV collagen belongs to the subclass of fibril-associated collagens with interrupted triple helices, which are composed of alternative triple helical and non-collagenous domains. Structural data show that these molecules interact with collagen fibrils and suggest that they might interact with cells. We have investigated the expression of type XIV collagen in bovine skin during development. Fetuses from 9 to 37 weeks were examined. Anti-type XIV collagen monoclonal antibody was produced, characterized, and used for immunofluorescence detection of the molecule. The localization of immunolabeling was analyzed by comparison with light and electron microscopic observations. In 9-week-old fetus, no type XIV collagen was found in the skin. From 19 weeks to birth, extensive immunofluorescence was observed on bundles of collagen fibrils in deep dermis. As shown by electron microscopy, this area exhibited bundles of collagen fibrils and cells with an abundant rough endoplasmic reticulum. In the upper dermis, a delicate fibrillar network of type XIV collagen was revealed by immunofluorescence around growing hair follicles at 19 and 24 weeks. Double labeling for type XIV collagen and fibronectin shows a more restricted pattern of expression of type XIV collagen in this area. The electron microscopic examination of skin of fetuses at these stages shows that the whole upper dermis is composed by a loose connective tissue containing scattered small bundles of collagen fibrils. Type XIV collagen was synthesized in the upper dermis between 24 weeks and birth. From this study, it appears that type XIV collagen expression is distinct from that of fibrillar collagens, at least during some developmental events. The prominent localization of type XIV collagen around growing hair follicles suggests a role for this molecule in epithelial-mesenchymal interactions.

Autoimmune recognition of cartilage collagens

Recent advances in basic research on the immune system and molecular biology of cartilage components have greatly increased our understanding of the role of autoimmunity in inflammatory diseases affecting joints, particularly rheumatoid arthritis. Many of these diseases are common and their complex pathogenesis probably involves a large number of genes polymorphic in the population as well as environmental factors. Characteristic features of inflammatory arthritis include expansion of the synovial tissue into a pannus containing lymphocytes and macrophages, autoimmune reactions against cartilage antigens, and erosion of cartilage. Since hyaline cartilage of the articular surfaces is the only structure within the joint known to contain joint-specific antigens this tissue is the prime suspect as the target of the autoimmune This review will first present the capacity of the immune system to discriminate between self and non-self structures, and then summarize our current understanding of the structures of cartilage collagens. Subsequently we will discuss how the immune system normally interacts with cartilage and how such interactions can lead to arthritis. We propose that collagen-induced arthritis (CIA) is valuable for understanding the autoimmune recognition of cartilage collagen which precedes the outbreak of arthritis and may perpetuate its chronicity, and serves as an animal model of rheumatoid arthritis.

Type V collagen: molecular structure and fibrillar organization of the chicken alpha 1(V) NH2-terminal domain, a putative regulator of corneal fibrillogenesis

Previous work from our laboratories has demonstrated that: (a) the striated collagen fibrils of the corneal stroma are heterotypic structures composed of type V collagen molecules coassembled along with those of type I collagen, (b) the high content of type V collagen within the corneal collagen fibrils is one factor responsible for the small, uniform fibrillar diameter (25 nm) characteristic of this tissue, (c) the completely processed form of type V collagen found within tissues retains a large noncollagenous region, termed the NH2-terminal domain, at the amino end of its alpha 1 chain, and (d) the NH2-terminal domain may contain at least some of the information for the observed regulation of fibril diameters. In the present investigation we have employed polyclonal antibodies against the retained NH2-terminal domain of the alpha 1(V) chain for immunohistochemical studies of embryonic avian corneas and for immunoscreening a chicken cDNA library. When combined with cDNA sequencing and molecular rotary shadowing, these approaches provide information on the molecular structure of the retained NH2-terminal domain as well as how this domain might function in the regulation of fibrillar structure. In immunofluorescence and immunoelectron microscopy analyses, the antibodies against the NH2-terminal domain react with type V molecules present within mature heterotypic fibrils of the corneal stroma. Thus, epitopes within at least a portion of this domain are exposed on the fibril surface. This is in marked contrast to mAbs which we have previously characterized as being directed against epitopes located in the major triple helical domain of the type V molecule. The helical epitopes recognized by these antibodies are antigenically masked on type V molecules that have been assembled into fibrils. Sequencing of the isolated cDNA clones has provided the conceptual amino acid sequence of the entire amino end of the alpha 1(V) procollagen chain. The sequence shows the location of what appear to be potential propeptidase cleavage sites. One of these, if preferentially used during processing of the type V procollagen molecule, can provide an explanation for the retention of the NH2-terminal domain in the completely processed molecule. The sequencing data also suggest that the NH2-terminal domain consists of several regions, providing a structure which fits well with that of the completely processed type V molecule as visualized by rotary shadowing.

Assembly of cartilage collagen fibrils is disrupted by overexpression of normal type II collagen in transgenic mice

Cartilage collagen fibrils, which are characterized by their thin, uniform diameters, are formed of a multicomponent system of three collagen types (II, IX, and XI) and interacting proteoglycans. We have used a genetic approach to test whether the proper assembly of this multiprotein structure was altered by overexpression of one of its normal components. Here we show that in transgenic mice in which the normal mouse alpha 1(II) collagen is overexpressed, thick abnormal collagen fibrils are generated. Mice that showed the highest expression of the transgene also displayed a larger proportion of abnormal fibrils and died at birth. We propose that an imbalance among the constituents of the cartilage collagen fibrils disrupts the mechanism that controls their assembly. The results show the applicability of the transgenic mice system to studies of complex multicomponent protein assemblies in intact animals.

Expression of simian virus 40 large T (tumor) oncogene in mouse chondrocytes induces cell proliferation without loss of the differentiated phenotype

We have infected primary embryonic mouse limb chondrocytes with a retrovirus carrying simian virus 40 early regions and have obtained a monoclonal mouse chondrocyte line, MC615, that was able to grow on culture dishes for at least 7 months and 20 passages. MC615 cells show expression of simian virus 40 large T (tumor) antigen and express markers characteristic of cartilage in vivo, such as types II, IX, and XI collagen, as well as cartilage aggrecan and link protein. These data show that cell growth induced by large T oncogene expression does not prevent the maintenance of the chondrocytic phenotype.

Osteoarthritis associated with mild chondrodysplasia in transgenic mice expressing alpha 1(IX) collagen chains with a central deletion

Type IX collagen, containing molecules of the three distinct polypeptides alpha 1(IX), alpha 2(IX), and alpha 3(IX), is an interesting hybrid extracellular matrix component in cartilage and eye tissues, with the properties of both a proteoglycan and a collagen. The alpha 1 (IX) chain has two forms, as a result of the tissue-specific utilization of two alternative promoters; the alpha 2(IX) chain carries a covalently attached glycosaminoglycan side chain. We have introduced a gene construct controlled by a tissue-specific promoter/enhancer and expressing a truncated alpha 1(IX) chain into mice. Examination of the offspring of two different founders revealed pathological changes similar to osteoarthritis in the articular cartilage of knee joints. In addition, mice homozygous for the transgene developed mild chondrodysplasia (i.e., mild dwarfism, anterior tonguing in the vertebral bodies, and ophthalmopathy). The relative ratio of transgene product to the endogenous alpha 1(IX) chain was approximately one in homozygotes and less than one in heterozygotes. Therefore, the phenotypic severity correlated well with the level of transgene expression. These findings suggest that mutations in type IX collagen genes may cause certain forms of osteoarthritis and chondrodysplasia in humans.

Molecular cloning of the human alpha 2(IX) collagen cDNA and assignment of the human COL9A2 gene to chromosome 1

Type IX collagen, a heterotrimer of alpha 1(IX), alpha 2(IX) and alpha 3(IX) chains, is a cartilage-specific fibril-associated collagen. In the process of characterizing genomic clones for the mouse alpha 2(IX) collagen gene four pairs of oligonucleotide primers designed for amplification of murine exon sequences were also utilized to construct cDNA clones for human alpha 2(IX) collagen spanning > 90% of the coding region. The amino acid and nucleotide sequence identities between human and chick are 78% and 71%, respectively. Localization of the COL9A2 gene to human chromosome 1 was subsequently performed using a panel of DNAs from human/rodent somatic cell hybrids.

Monoclonal antibodies against two epitopes in the human alpha 1 (IX) collagen chain

Type IX collagen is a component of cartilage and vitreous humor. Its structure and matrix localization suggest it may serve to mediate interactions between fibrillar collagen, proteoglycan and other matrix components. Consequently, abnormalities in type IX collagen may result in chondrodysplasia. In this paper we describe the preparation and use of two monoclonal antibodies which recognize peptide sequences within the human cartilage alpha 1 (IX) collagen chain. Antibody 23-5D1 is highly sensitive and highly specific. It permits the immunoblot detection of type IX collagen extracted from milligram amounts of normal and chondrodysplastic cartilage; it also identifies the "short" form of the alpha 1 (IX) chain in human vitreous humor. Antibody 37-10H7 is highly specific, but of low sensitivity. It was used to make the new observation that an N-linked oligosaccharide is present in the amino-terminal globular domain of the alpha 1 (IX) chain. We anticipate that these antibodies may be valuable tools in the study of human and other mammalian chondrodysplasias.

Structure and binding properties of collagen type XIV isolated from human placenta

Collagen XIV was isolated from neutral salt extracts of human placenta and purified by several chromatographic steps including affinity binding to heparin. The same procedures also led to the purification of a tissue form of fibronectin. Collagen XIV was demonstrated by partial sequence analysis of its Col1 and Col2 domains and by electron microscopy to be a disulphide-linked molecule with a characteristic cross-shape. The individual chains had a size of approximately 210 kD, which was reduced to approximately 180 kD (domain NC3) after treatment with bacterial collagenase. Specific antibodies mainly to NC3 epitopes were obtained by affinity chromatography and used in tissue and cell analyses by immunoblotting and radioimmunoassays. Two sequences from NC3 were identified on fragments obtained after trypsin cleavage. They were identical to cDNA-derived sequences of undulin, a noncollagenous extracellular matrix protein. This suggests that collagen XIV and undulin may be different splice variants from the same gene. Heparin binding was confirmed in ligand assays with a large basement membrane heparan sulphate proteoglycan. This binding could be inhibited by heparin and heparan sulphate but not by chondroitin sulphate. In addition, collagen XIV bound to the triple helical domain of collagen VI. The interactions with heparin sulphate proteoglycan and collagen VI were not shared by the NC3 domain, or by reduced and alkylated collagen XIV. No or only low binding was observed for collagens I-V, pN-collagens I and III, and several noncollagenous matrix proteins, including laminin, recombinant nidogen, BM-40/osteonectin, plasma and tissue fibronectin, vitronectin, and von Willebrand factor. Insignificant activity was also shown in cell attachment assays with nine established cell lines.

Immunohistochemical localization of collagenous proteins in cartilaginous tumors: characteristic distribution of type IX collagen

The distinctive tissue localization of collagen types, particularly of type IX collagen in human cartilaginous tumors (10 cases of enchondroma and 15 cases of chondrosarcoma including 3 cases of secondary chondrosarcoma) was examined immunohistochemically using affinity-purified antibodies against types I, II, III, V, VI, and IX collagen, in comparison with that in human fetal cartilage. In fetal cartilage matrix, types II and IX collagen were diffusely distributed, while types I, III, and V collagens were not present. In the matrices of enchondromas and primary chondrosarcomas, types II and IX collagens were also diffusely distributed, but with some areas of irregular type IX collagen deposits. The secondary chondrosarcoma simulated normal fetal cartilage in the distribution pattern of types II and IX collagen, unlike the pattern in primary chondrosarcoma, where types II and IX collagen were decreased and poorly immunostained, whereas non-cartilaginous interstitial collagens (I, III, and V) appeared diffusely in the matrix, increasing with the grade of malignancy. These findings suggest that neoplastic cartilage is characterized initially by an uneven distribution of type IX collagen, prior to any alteration of other types of collagen; the diverse expressions of intercellular components in cartilaginous tumors may be one indicator for malignancy.

Type II collagen during cartilage and corneal development: immunohistochemical analysis with an anti-telopeptide antibody

We have examined the pattern of immunoreactivity of a monoclonal antibody, II-5B2, with specificity for an epitope which resides within the NH2-terminal extension peptide (telopeptide) of the avian type II collagen molecule. This epitope is available in regions of matrix where de novo synthesis of the molecule is ongoing, but not where synthesis has ceased and maturation and crosslink formation have occurred. Within the cartilaginous growth plate, the epitope disappears from the matrix soon after the chondrocytes become hypertrophic; within the cornea, the epitope disappears subjacent to the epithelium. The II-5B2 epitope is not made available by a variety of procedures shown to remove potentially masking substances and to disrupt fibrillar organization. It is rendered available, however, when covalent crosslink formation between collagen molecules is blocked through administration of beta-aminopropionitrile or penicillamine. In contrast, the epitope of another monoclonal antibody against type II collagen, II-II6B3, which resides in the triple-helical domain of the molecule, in cartilage is present throughout the growth plate including the hypertrophic zone, and in cornea extends for a considerable distance into the stroma. Thus, it is available for antibody binding regardless of fibril maturation and crosslinking. These data suggest that the II-5B2 epitope becomes unavailable when the telopeptide becomes crosslinked. By using these two monoclonal antibodies in serial sections, one can establish the crosslinking pattern of type II collagen in the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Chicken tibial dyschondroplasia: a limb mutant with two growth plates and possible defects of collagen crosslinking

In the cartilaginous epiphyseal growth plate, extracellular matrix molecules such as collagens are believed to play important roles during both normal and abnormal development. One defect of the epiphyseal plate occurs in chickens with a condition termed tibial dyschondroplasia (TD). This abnormality occurs in certain strains of juvenile chickens and other rapidly developing animals. It is characterized by the presence of a mass of avascular, uncalcified cartilage which is retained in the proximal metaphysis of the tibiotarsus. To elucidate the developmental events which may be involved in this lesion, we have performed both immunohistochemistry and in situ hybridizations for collagen types II and X, known components of the extracellular matrix of the growth plate. By immunohistochemical analyses, the TD lesion contains both of these collagen types; therefore, the presence of these molecules per se is not sufficient for calcification of vascularization to occur. Since type X collagen is expressed exclusively in hypertrophic cartilage, the chondrocytes in the lesion must have undergone hypertrophy before their developmental arrest. The matrix of the lesion also reacted with a monoclonal antibody which is directed against an epitope in the NH2-terminal telopeptide of the alpha 1(II) chain. Our previous data suggest that this epitope is rendered unavailable in type II collagen which has undergone crosslink formation; its availability in the lesion suggests that crosslinking may be abnormal. Lastly, analyses by in situ hybridization failed to detect mRNA for either type II or type X collagen within the lesion, but chondrocytes distal to the lesion do contain mRNAs for these collagens in a spatial pattern suggesting the presence of a second growth plate.

Chondrons from articular cartilage. V. Immunohistochemical evaluation of type VI collagen organisation in isolated chondrons by light, confocal and electron microscopy

The pericellular microenvironment around articular cartilage chondrocytes must play a key role in regulating the interaction between the cell and its extracellular matrix. The potential contribution of type VI collagen to this interaction was investigated in this study using isolated canine tibial chondrons embedded in agarose monolayers. The immunohistochemical distribution of an anti-type VI collagen antibody was assessed in these preparations using fluorescence, peroxidase and gold particle probes in combination with light, confocal and transmission electron microscopy. Light and confocal microscopy both showed type VI collagen concentrated in the pericellular capsule and matrix around the chondrocyte with reduced staining in the tail region and the interconnecting segments between adjacent chondrons. Minimal staining was recorded in the territorial and interterritorial matrices. At higher resolution, type VI collagen appeared both as microfibrils and as amorphous deposits that accumulated at the junction of intersecting capsular fibres and microfibrils. Electron microscopy also showed type VI collagen anchored to the chondrocyte membrane at the articular pole of the pericellular capsule and tethered to the radial collagen network through the tail at the basal pole of the capsule. We suggest that type VI collagen plays a dual role in the maintenance of chondron integrity. First, it could bind to the radial collagen network and stabilise the collagens, proteoglycans and glycoproteins of the pericellular microenvironment. Secondly, specific cell surface receptors exist, which could mediate the interaction between the chondrocyte and type VI collagen, providing firm anchorage and signalling potentials between the pericellular matrix and the cell nucleus. In this way type VI collagen could provide a close functional interrelationship between the chondrocyte, its pericellular microenvironment and the load bearing extracellular matrix of adult articular cartilage.

A major oligomeric fibroblast proteoglycan identified as a novel large form of type-XII collagen

Cultured chick embryo skin fibroblasts release a major component with a native molecular mass of about 1 MDa, which resolves into three polypeptide bands of about 300, 350 and 600 kDa upon reduction. We report here the purification of this oligomeric protein and show, by means of polyclonal and monoclonal antibodies, that its three polypeptide constituents are closely related. The 600-kDa polypeptide is likely to be a dimer of two smaller subunits which are cross-linked by non-reducible bonds. By electron microscopy, isolated oligomeric molecules exhibit a novel cruciform structure with a large central globular domain. One arm has the shape of a thin rod about 70 nm in length. The three other arms are thicker, longer (90 nm) and flexible, and carry a prominent double globule at their distal ends. Collagenase treatment of the oligomeric fibroblast protein yields two resistant fragments of about 270 kDa and 320 kDa. The intact 350-kDa and 600-kDa (but not the 300-kDa) polypeptides are chondroitinase sensitive and labeled by metabolic incorporation of [35S]sulfate; collagenase treatment does not remove any [35S] sulfate. Hence, the intact fibroblast protein has glycosaminoglycan chains attached to its non-collagenous domain. Three amino acid sequences obtained from chymotryptic fragments of the fibroblast protein correspond to sequences predicted for chick type-XII collagen from its full-length cDNA [Yamagata, M., Yamada, K. M., Yamada, S. S., Shinomura, T., Tanaka, H., Nishida, Y., Obara, M. & Kimata, K. (1991) J. Cell Biol. 115, 209-221]. However, the novel fibroblast protein described here differs significantly from previously isolated forms of type-XII collagen: its subunits are larger by one third, and it is a proteoglycan.

Isolation and characterization of type IX collagen-proteoglycan from the Swarm rat chondrosarcoma

Type IX collagen was partially purified from the Swarm rat chondrosarcoma by a series of a conventional salting-out procedures. The preparation was further separated by anion exchange chromatography into an unbound and a bound fraction in an A230 ratio of about 5:1. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the bound fraction appeared as a broad band, whose molecular mass ranged from 250 to 270 kDa. Digestion with chondroitinase ABC reduced the apparent molecular mass of the bound fraction to about 250 kDa, a value comparable to the molecular mass of the unbound fraction. Tryptic peptide maps of the protein moieties of unbound and bound forms showed that their molecular structures were basically identical. A monoclonal antibody specific for LMW, one of the pepsin-resistant fragments of the rat sarcoma type IX, reacted with both the unbound and bound fractions. Together the results indicate that the unbound and bound fractions represent a type IX collagen devoid of the chondroitin sulfate chain and its proteoglycan form with covalently bound chondroitin sulfate, respectively. The extent of glycosaminoglycan attachment to type IX collagen molecules in rat chondrosarcoma (about 16%) is quite different from the extents described in chick embryo cartilage (about 80%), chick vitreous humour (100%) and bovine cartilage (less than 5%). Further studies on the neoplastic tissue will offer additional information regarding the biological basis and biological consequences of the glycosaminoglycan attachment to type IX collagen molecules.

Cloning and chromosomal location of human alpha 1(XVI) collagen

We have characterized cDNA clones that encode a newly discovered collagenous polypeptide. A 4-kilobase (kb) cDNA clone was initially isolated by screening a human fibroblast cDNA library with a probe encoding the collagenous domain of the human alpha 3(VI) collagen. Subsequent screening of another fibroblast cDNA library yielded overlapping clones having a total length of 5.4 kb, which contained an open reading frame of 1603 amino acids including a 21-amino acid signal peptide. The predicted polypeptide consists of 10 collagenous domains 15-422 amino acids long, which were interspersed with 11 noncollagenous (NC) domains. Except for a large N-terminal NC11 domain of 312 residues, most of the NC domains were short (11-39 residues) and cysteine-rich. The overall structural arrangement differed significantly from other known collagen chains. Further analysis indicated that the deduced polypeptide exhibited several structural features characteristically seen in members of the fibril-associated collagen, types IX, XII, and XIV. In addition, the cysteine-rich motifs in the NC domains resembled those found in the cuticle collagen of Caenorhabditis elegans. Northern blot analyses showed hybridization of the cDNA to a 5.5-kb mRNA in human fibroblasts and keratinocytes. The gene was localized by in situ hybridization to band p34-35 of human chromosome 1. The data clearly support the conclusion that the cDNA encodes a collagen chain that has not been previously described. We suggest that the cDNA clones encode the alpha 1 chain of type XVI collagen.

Notochord of chick embryos secretes short-form type IX collagen prior to the onset of vertebral chondrogenesis

The notochord of embryonic chicks produces type IX collagen, as well as type II collagen, prior to the onset of vertebral chondrogenesis. To address the question of whether the notochord secretes the "long-form" type IX collagen found in cartilage or the "short-form" type IX found in the cornea and vitreous humor, we examined immunoreactivity of the notochordal type IX collagen using two different monoclonal antibodies. The antibody 2C2 recognizes an epitope close to the carboxyl-terminus of the HMW fragment, which is present in both the long- and short-form type IX collagens, whereas another antibody 4D6 recognizes an epitope in the NC4 domain of the long-form type IX collagen, which is absent in the short-form type IX collagen. Therefore, the long-form is recognized by its reaction with both 2C2 and 4D6, while the short-form by its reaction with only 2C2 and no reaction with 4D6. Immunostaining of vertebral sections with 2C2 shows an identical distribution of staining with that for type II collagen, although the staining with 2C2 is less intense. The 2C2-reactive type IX collagen is found within the notochord at stage 14 and in the notochordal sheath at stage 20. Deposition of this collagen in the perinotochordal matrix increases with time and reaches a level comparable with that for type II at stage 31. In contrast, the 4D6-reactive type IX collagen is not found within the notochord nor in the notochordal sheath.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of type II collagen, long form alpha 1(IX) collagen, and short form alpha 1(IX) collagen transcripts in the developing chick notochord and axial skeleton

In this study we compare, by in situ hybridization, the spatial and temporal expression patterns of transcripts of avian type II collagen and the long and short forms of the (alpha 1) chain of type IX collagen during the development of the notochord and axial skeleton. We observed type II collagen and short form type IX collagen transcripts in the developing (stage 25-28) nonchondrogenic notochord. Conversely, long form type IX transcripts were not detectable in the notochord or perinotochordal sheath. Interestingly, all three transcripts colocalized in the developing chondrogenic vertebrae of the axial skeleton as well as in the chondrocranium and Meckel's cartilage. The expression of the short form of type IX collagen in these regions was more restricted than that of the long form. This report provides additional support for a complex regulatory pathway of cartilage marker gene expression in chondrogenic vs. nonchondrogenic tissues during avian embryogenesis.

Extraction and characterisation of the intact form of bovine vitreous type IX collagen

We provide the first biochemical characterisation of intact type IX collagen extracted from bovine vitreous. It possesses a shortened alpha 1(IX) chain (M(r) 64K) compared to its cartilage counterpart (M(r) 84K). All the vitreous type IX collagen is in a proteoglycan form, its glycosaminoglycan constituent being a chondroitin/dermatan sulphate component of M(r) 15-60K attached to the alpha 2(IX) chain. This contrasts with previous findings in chick vitreous where a very long glycosaminoglycan chain of M(r) approximately 350K was demonstrated.

Coordinate inhibition of alkaline phosphatase and type X collagen syntheses by 1,25-dihydroxyvitamin D3 in primary cultured hypertrophic chondrocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (2.3 x 10(-12) - 1.4 x 10(-6) [M]) on alkaline phosphatase, collagen, and cell proliferation were examined in primary cultured hypertrophic chondrocytes prepared from the distal epiphyseal growth plate of the tibias of 12-day chick embryos. 1,25(OH)2D3 showed time- and dose-dependent inhibitory effects on the alkaline phosphatase and collagen levels. The inhibition of alkaline phosphatase activity became detectable at 2 x 10(-11) [M] and reached 10% of control at 10(-7) [M]. The concentration of 1,25(OH)2D3 giving a 50% inhibition of the enzyme level was approximately 3 x 10(-10) [M]. Of the two extracellular collagen pools, a cell-associated matrix pool showed a more dramatic decrease (to 10% of control) than a culture medium pool (to 50% of control) at increased 1,25(OH)2D3 concentrations. The degree of inhibition was different for each type of chondrocyte-specific collagen (types II, IX, X, and XI). Types II and IX were inhibited in a parallel manner to only 60-80% of control. On the other hand, types X and XI were more greatly reduced up to 10% of control, and their dose-dependent inhibitory curves were similar to that of alkaline phosphatase. On cell proliferation, 1,25(OH)2D3 had a biphasic effect: stimulation at 10(-10)-10(-8) [M] and inhibition at higher levels. The results revealed the significant involvement of 1,25(OH)2D3 in the metabolism of two probable calcification-related products, alkaline phosphatase and type X collagen.

Cloning of the chicken alpha 3(IX) collagen chain completes the primary structure of type IX collagen

Type IX collagen is composed of three genetically distinct polypeptides that contain several collagenous and non-collagenous domains. The alpha 2(IX) chain also contains a covalently bound glycosaminoglycan side chain. Type IX collagen is located on the surface of collagen fibrils of both hyaline cartilage and vitreous humor, such that one of the collagenous domains (COL3) projects from the surface of the fibril in a periodic manner. We have cloned and sequenced a full-length cDNA for the chicken alpha 3(IX) collagen chain from a cartilage cDNA library. Together with the sequence of the alpha 1(IX) and alpha 2(IX) chains, this completes the primary structure of type IX collagen for one species. These sequences will be useful to better understand the mechanism of triple-helix formation in type IX collagen and the nature of type II and type IX collagen interactions in fibril formation.

Electron-microscopic localization of type II, IX, and V collagen in the organ of Corti of the gerbil

The presence of types II, IX and V collagen was probed in the organ of Corti of the adult gerbil cochlea by use of immunocytochemistry at the light- and electron-microscopic levels. Type II collagen is found in the connective tissues of the osseous spiral lamina and spiral limbus. In the region of the sensory hair cells it is present in the tectorial membrane and antibodies bind to the thick unbranched radial fibers. Type IX collagen co-localizes with type II collagen in the tectorial membrane, where antibodies bind to the thick unbranched radial fibers. Type V collagen is present in the connective tissue of the spiral limbus, the osseous spiral lamina, the eighth nerve, and the tectorial membrane. In the tectorial membrane, the staining with antibodies to type V collagen is more diffuse than that seen for types II and IX collagen and antibodies to type V bind to the thin, highly branched fibers in which the thick fibers are embedded. The results indicate that collagens characteristic of cartilage are localized in the organ of Corti. Within the tectorial membrane, types II and IX collagen form heterotypic thick fibers embedded in a reticular network of type V collagen fibers. These collagens form a highly structured matrix which contributes to the rigidity of the tectorial membrane and allow it to withstand the physical stresses associated with transmission of the stimuli necessary for sensory transduction.

Mammalian vitreous humor contains networks of hyaluronan molecules: electron microscopic analysis using the hyaluronan-binding region (G1) of aggrecan and link protein

Vitreous humor from human, bovine, and chicken eyes was analyzed by rotary shadowing to characterize further the supramolecular organization of the gel-like matrix which forms this tissue. Extensive filamentous networks, distinct from collagen fibrils, were found in both human and bovine vitreous but not in chicken vitreous. The networks consisted of branching structures of various diameters, due to variable numbers of hyaluronan molecules being laterally associated with each other and apparently giving rise to a three-dimensional lattice. These networks could be decorated in a specific and regular manner by the hyaluronan-binding region called G1 purified from bovine nasal septum cartilage. The extent of decoration of hyaluronan was dependent on the relative concentration of G1. In the presence of an excess of G1 the networks were destabilized giving rise to individual unbranched hyaluronan chains of varying length that were saturated with G1. One or more globular proteins, as yet uncharacterized, were seen interacting with the hyaluronan networks, often at branch points. These proteins may serve to stabilize the three-dimensional structure of the matrix although highly ordered networks were also observed without globular proteins. Link protein, which also binds to hyaluronan, bound to the networks in a fashion clearly distinct from G1. Neither G1 nor link protein bound directly to human or bovine vitreous collagen fibrils. However, link protein did bind extensively to the glycosaminoglycan coat of chicken vitreous collagen fibrils described previously (D. W. Wright, and R. Mayne J. Ultrastruct. Mol. Struct. Res. 100, 224-234, 1988), while G1 did not. Digestion of the chicken vitreous collagen fibrils with Streptomyces hyaluronidase did not result in the removal of the glycosaminoglycan coat of the collagen fibrils nor did it affect the binding of G1 or link protein to the fibrils, indicating that hyaluronan is not a component of this structure. These studies demonstrate that proteins with specific binding properties can be used as probes to investigate the structure of the native vitreous humor gel from several species and suggest that this method potentially can be used for structural studies of other connective tissue matrices.

Type II and type IX collagen form heterotypic fibers in the tectorial membrane of the inner ear

The presence of type II and IX collagen in the adult gerbil inner ear was probed by use of preembedding and post-embedding immunocytochemistry. Monoclonal antibodies to type II and IX collagen both label the tectorial membrane, an acellular structure which lies over the cochlear sensory hair cells and plays an essential role in the transduction process. At the light microscopic level, the antibodies are localized throughout the tectorial membrane. At the electron microscopic level, antibodies against types II and IX collagen are co-localized over the thick unbranched (Type A) radial fibers but not over the thin highly branched (Type B) fibers in which the thick fibers are embedded. Thus, the tectorial membrane of the cochlea represents another non-cartilaginous structure in which type II and IX collagen are present and arranged in heterotypic fibers. The organization of these fibers into bundles, meshworks and layers results in the formation of a structure with the unique properties necessary to withstand mechanical stresses associated with sensory transduction.

Monoclonal antibodies that distinguish avian type I and type III collagens: isolation, characterization and immunolocalization in various tissues

Monoclonal antibodies were prepared that were specific for chicken type I and type III collagens. The specificity of these antibodies was determined by ELISA, inhibition ELISA, and immunoblot assays. The results showed that the monoclonal antibodies were specific for their respective antigens without significant cross reactivity to other types of collagen. An analysis of the location of the epitopes by rotary shadowing that a monoclonal antibody for type I collagen (called DD4) recognized type I procollagen close to the large globular domain at the carboxyl terminus of the molecule. A monoclonal antibody for type III collagen (called 3B2) recognized both the intact type III molecule and also the TCA fragment of type III collagen after mammalian collagenase digestion. The epitope was located approximately one-fifth of the distance from the amino-terminus of the intact molecule. The monoclonal antibodies were used for immunolocalization of type I and type III collagens in cryosections of heart, aorta, kidney, liver, thymus, skin, gizzard and myotendinous junction. In heart, aorta, kidney, liver, thymus and skin, type I and III collagens were colocalized in the connective tissue of each organ. In contrast, gizzard and myotendinous junction showed distinctly different staining patterns for the distribution of type I and type III collagen. The two monoclonal antibodies reported here are potentially useful reagents to study fibril formation involving type I and type III collagens.

Localization of type II, IX and V collagen in the inner ear

Types II and IX collagen are traditionally considered cartilage collagens; however, within the inner ear, types II and IX collagen have a more diverse distribution. In the adult gerbil, type II collagen is the major fibrillar component. In the otic capsule it is present surrounding the osteocytes embedded and branching in the periosteal layer, in the cartilaginous rests of the enchondral layer, and in the endosteal layer bordering the membranous labyrinth. In the regions of the sensory cells, type II collagen is found in the osseous spiral lamina, the connective tissue of the spiral limbus, the subepithelial tissue of the maculae in the vestibule and the cristae in the ampullae, and in the spiral ligament. It is present in the non-cartilaginous and acellular structures of the tectorial membrane over the cochlear hair cells and the vestibular membrane lining the semicircular canals. Type IX collagen, when present, in all cases co-localizes with type II collagen but is found in more limited regions. It is found only in the cartilaginous rests of the enchondral bone, the tectorial membrane and the vestibular membrane. Type V-like collagen, a connective tissue collagen, is found to have a complementary localization to types II and IX collagen within the interstitial bone of the otic capsule, the osseous spiral lamina and the tectorial membrane, but it is absent from the vestibular membrane. This report is the first documenting the co-localization of types II and IX collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

The collagens of articular cartilage

Articular cartilage contains at least five genetically distinct types of collagen. Types II, IX, and XI are cartilage-specific and are cross-linked together in a copolymeric network that forms the extracellular framework of the tissue. Fibrils of type II collagen provide the basic architecture. Type XI, a quantitatively minor fibril-forming collagen, is probably copolymerized with type II collagen in the matrix. Type IX collagen accounts for approximately 1% of the collagenous protein in adult articular cartilage and its molecules exist in the tissue covalently linked to the surface of type II collagen fibrils. Its suspected functions include regulating fibril diameters and mediating fibril-fibril and fibril-proteoglycan interactions. Stromelysin, a matrix metalloproteinase, was recently shown to degrade type IX collagen. This action may cause the collagen network swelling seen in articular cartilage in early experimental osteoarthritis, (OA). Collagen type X is restricted to the underlying calcified zone of articular cartilage, a zone that exhibits active remodeling in joints with OA. Degradation products of the various cartilage collagens show promise as molecular markers of joint disease.

Cloning of a cDNA for a new member of the class of fibril-associated collagens with interrupted triple helices

cDNA from embryonic chick skin has been isolated and characterized which encodes a novel member of the FACIT (fibril-associated collagen with interrupted triple helices) group whose other known members are collagen types IX and XII. Nucleotide sequence analysis of the cDNA, combined with characterization of a pepsin-resistant fragment of the protein from embryonic chick skin, demonstrates that the collagen chain is more closely related to the chain of type XII collagen than to those of type IX. It is most similar to a collagen, type XIV, recently identified in bovine skin. It is possible, therefore, that the cDNA codes for a chain of chicken type XIV collagen. From the additional data on molecular structure obtained by sequencing the cDNA, the FACIT family appears to consist of at least two classes of molecules: one of which contains the three chains of type IX collagen, and a second which includes the chains of collagen types XII and XIV.

Mammalian cartilage synthesizes both proteoglycan and non-proteoglycan forms of type IX collagen

Bovine epiphysial cartilage synthesizes both proteoglycan (PG) and non-PG forms of type IX collagen in a ratio of approx. 2:1. The PG form with its attached glycosaminoglycan on the alpha 2(IX) chain is the major form in the medium, whereas both forms are found in the tissue. The results are discussed with regard to cartilage matrix organization.

Matrix in cartilage and bone development: current views on the function and regulation of major organic components

Study of the growth and development of cartilage and bone has been difficult because the structure of the tissues makes biological experiments hard to conduct. Recent advances in molecular biology have offered new possibilities for studying these processes. Many cartilage and bone specific cDNAs have been cloned and characterized and consequently used to localize the corresponding mRNAs in tissue sections. Developing cartilage and bone serve as a model for the study of extracellular matrix gene regulation during the proliferation, growth and differentiation of connective tissue cells. Normal skeletal growth and development are regulated by both systemic and local factors. The effects of many systemic hormones on bone metabolism have been studied extensively, but the pathways triggered by these hormones in the target cells are less well known. Recent evidence suggests that some growth factors, such as TGF-beta, IGFs and PDGF, act as local regulators of cartilage and bone metabolism. The different extracellular matrix components, e.g. collagens, are expressed differently in distinct cell types and developmental stages during cartilage and bone development. This model, therefore, facilitates the study of relations between the production of the various extracellular matrix components and the growth factors and the proto-oncogenes which may regulate them. Existing knowledge of the expression of major cartilage and bone components and their regulation during growth, differentiation and development is reviewed. An understanding of the normal growth and development of cartilage and bone is fundamental for elucidating the mechanisms underlying the various diseases -- both hereditary and acquired -- affecting the human skeleton.

Two type XII-like collagens localize to the surface of banded collagen fibrils

Two recently identified collagen molecules, termed twelve-like A and twelve-like B (TL-A and TL-B) have properties similar to type XII collagen. These molecules have been localized in human and calf tissues by immunoelectron microscopy. The observations strongly suggest that both molecules are located along the surface of banded collagen fibers. The epitopes recognized by the antibodies are contained in large, nontriple-helical domains at one end of the collagen helix. The epitopes are visualized at a distance from the surface of the banded fibers roughly equal to the length of the nonhelical domains, suggesting that the nonhelical domains extend from the fibril, while the triple-helical domains are likely to bind directly to the fibril surface. Occasionally, both TL-A and TL-B demonstrate periodic distribution along the fibril surface. The period corresponds to the primary interband distance of the banded fibrils. Not all fibrils in a fiber bundle are labeled, nor is the labeling continuous along the length of labeled fibrils. Simultaneous labeling of TL-A and type VI collagen only rarely shows colocalization, suggesting that TL-A and TL-B do not mediate interactions between the type VI collagen beaded filaments and banded collagen fibrils. Also, interfibrillar distances are approximately equivalent in the presence and absence of these type XII-like molecules. While the results do not directly indicate a specific function for these molecules, the localization at the fibril surface suggests that they mediate interactions between the fibrils and other matrix macromolecules or with cells.

FACIT collagens: diverse molecular bridges in extracellular matrices

The collagens form a large family of proteins. Collagen fibrils, composed of staggered arrays of fibrillar collagen molecules (types I, II, III, V and XI), provide a supporting scaffold for extracellular matrices of connective tissues. The non-fibrillar collagens are less abundant than the fibrillar collagens, but it is becoming clear that they have important functions in the matrix. Recently, a group with unique structural characteristics has been defined and named the FACIT (Fibril-Associated Collagens with Interrupted Triple-helices) group. There is evidence that these collagens may serve as molecular bridges that are important for the organization and stability of extracellular matrices.

Isolation of human type X collagen and immunolocalization in fetal human cartilage

Type X collagen was extracted with 1 M NaCl and 10 mM dithiothreitol at neutral pH from fetal human growth plate cartilage and purified to homogeneity by gel filtration and anion-exchange chromatography. The purified protein migrates in SDS/polyacrylamide gels with an apparent Mr of 66,000 under reducing conditions, and as a high-Mr oligomer under non-reducing conditions. Purified collagenase digests most of the molecule; pepsin digestion at 4 degrees C decreases the Mr of the monomer to 53,000. A rabbit antiserum was raised against purified human type X collagen; the IgG fraction was specific for this collagen by criteria of ELISA and immunoblotting after absorption with collagen types I, II, VI, IX and XI. Immunohistological studies localized type X collagen exclusively in the zone of hypertrophic and calcifying cartilage.

cDNA analysis predicts a cornea-specific collagen

In the development of chicken corneal stroma, two or more collagens often interact, either as constituents of a single heterotypic fibril or as components of the fibril surface. The latter, fibril-associated collagens, may facilitate interactions between fibrils and the surrounding extracellular matrix or between fibrils themselves. In an effort to isolate putative nonfibrillar collagens that may have such a function, we screened a 13-day embryonic cornea cDNA library under reduced stringency conditions, using a cDNA probe for a collagenous domain of type XII collagen. We isolated a 4.2-kilobase (kb) cDNA that predicts a "collagenous" protein that has three unusual, if not unique, features. (i) The putative polypeptide encoded by this cDNA has a structural arrangement in which numerous stretches of Gly-Xaa-Yaa triplets, typical of collagens, are interrupted by non-Gly-Xaa-Yaa regions. One of the potential triple-helical domains is 246 amino acids long, but most are much smaller, consisting of 15-36 amino acids. Many are very rich in the helix-stabilizing imino acid proline. (ii) Northern blot analyses demonstrated strong cDNA hybridization to a 6.8-kb mRNA whose expression is restricted to the cornea. No hybridization was observed to mRNAs from the nine other tissues used in these analyses, even with extended exposure of the film. (iii) The cDNA contains a short (less than or equal to 425-base-pair) sequence in the 3' untranslated region of the 6.8-kb mRNA that hybridizes to a 7.8-kb mRNA that has a wide tissue distribution.