Monoclonal antibody against chicken type IX collagen: preparation, characterization, and recognition of the intact form of type IX collagen secreted by chondrocytes

Mechanical loading due to muscle movement regulates establishment of the collagen network in the developing murine skeleton

Mechanical loading is critical for collagen network maintenance and remodelling in adult skeletal tissues, but the role of loading in collagen network formation during development is poorly understood. We test the hypothesis that mechanical loading is necessary for the onset and maturation of spatial localization and structure of collagens in prenatal cartilage and bone, using in vivo and in vitro mouse models of altered loading. The majority of collagens studied was aberrant in structure or localization, or both, when skeletal muscle was absent in vivo. Using in vitro bioreactor culture system, we demonstrate that mechanical loading directly modulates the spatial localization and structure of collagens II and X. Furthermore, we show that mechanical loading in vitro rescues aspects of the development of collagens II and X from the effects of fetal immobility. In conclusion, our findings show that mechanical loading is a critical determinant of collagen network establishment during prenatal skeletal development.

Matrilin-1 is essential for zebrafish development by facilitating collagen II secretion

Matrilin-1 is the prototypical member of the matrilin protein family and is highly expressed in cartilage. However, gene targeting of matrilin-1 in mouse did not lead to pronounced phenotypes. Here we used the zebrafish as an alternative model to study matrilin function in vivo. Matrilin-1 displays a multiphasic expression during zebrafish development. In an early phase, with peak expression at about 15 h post-fertilization, matrilin-1 is present throughout the zebrafish embryo with exception of the notochord. Later, when the skeleton develops, matrilin-1 is expressed mainly in cartilage. Morpholino knockdown of matrilin-1 results both in overall growth defects and in disturbances in the formation of the craniofacial cartilage, most prominently loss of collagen II deposition. In fish with mild phenotypes, certain cartilage extracellular matrix components were present, but the tissue did not show features characteristic for cartilage. The cells showed endoplasmic reticulum aberrations but no activation of XBP-1, a marker for endoplasmic reticulum stress. In severe phenotypes nearly all chondrocytes died. During the early expression phase the matrilin-1 knockdown had no effects on cell morphology, but increased cell death was observed. In addition, the broad deposition of collagen II was largely abolished. Interestingly, the early phenotype could be rescued by the co-injection of mRNA coding for the von Willebrand factor C domain of collagen IIα1a, indicating that the functional loss of this domain occurs as a consequence of matrilin-1 deficiency. The results show that matrilin-1 is indispensible for zebrafish cartilage formation and plays a role in the early collagen II-dependent developmental events.

Chemical pretreatment of growth plate cartilage increases immunofluorescence sensitivity

Immunofluorescence detection of proteins in growth plate cartilage is often unsuccessful because of innate autofluorescence, fixative-induced fluorescence, and dense cartilage matrix, which can inhibit antibody penetration. To overcome these limitations, the authors have tested various chemical pretreatments, including the autofluorescence quencher sodium borohydride, the antigen retrieval method of boiling sodium citrate, sugar-degrading enzymes (hyaluronidase, heparinase, and chondroitinase), and the proteolytic enzyme protease XXIV. Here the authors show that, in most cases, background fluorescence in cartilage is the primary obstacle to high-quality imaging. Blocking intrinsic fluorescence of the specimen in combination with specific pretreatments allows visualization using antibodies that previously did not generate a robust signal in the growth plate. Each antibody requires a specific combination of chemical pretreatments that must be empirically determined to achieve optimal staining levels.

Skeletal dysplasias associated with mild myopathy-a clinical and molecular review

Musculoskeletal system is a complex assembly of tissues which acts as scaffold for the body and enables locomotion. It is often overlooked that different components of this system may biomechanically interact and affect each other. Skeletal dysplasias are diseases predominantly affecting the development of the osseous skeleton. However, in some cases skeletal dysplasia patients are referred to neuromuscular clinics prior to the correct skeletal diagnosis. The muscular complications seen in these cases are usually mild and may stem directly from the muscle defect and/or from the altered interactions between the individual components of the musculoskeletal system. A correct early diagnosis may enable better management of the patients and a better quality of life. This paper attempts to summarise the different components of the musculoskeletal system which are affected in skeletal dysplasias and lists several interesting examples of such diseases in order to enable better understanding of the complexity of human musculoskeletal system.

Type IX collagen gene mutations can result in multiple epiphyseal dysplasia that is associated with osteochondritis dissecans and a mild myopathy

Multiple epiphyseal dysplasia (MED) is a clinically variable and genetically heterogeneous disease that is characterized by mild short stature and early onset osteoarthritis. Autosomal dominant forms are caused by mutations in the genes that encode type IX collagen, cartilage oligomeric matrix protein, and matrilin-3: COL9A1, COL9A2, COL9A3, COMP, and MATN3, respectively. Splicing mutations have been identified in all three genes encoding type IX collagen and are restricted to specific exons encoding an equivalent region of the COL3 domain in all three alpha(IX) chains. MED has been associated with mild myopathy in some families, in particular one family with a COL9A3 mutation and two families with C-terminal COMP mutations. In this study we have identified COL9A2 mutations in two families with MED that also have osteochondritis dissecans and mild myopathy. This study therefore extends the range of gene-mutations that can cause MED-related myopathy. (c) 2010 Wiley-Liss, Inc.

Developmental regulation of muscleblind-like (MBNL) gene expression in the chicken embryo retina

Muscleblind-like (MBNL) is a CCCH zinc finger-containing RNA-binding protein required for the development of both muscle and photoreceptors in Drosophila; it is conserved evolutionarily, and it is associated in humans with the muscular disease myotonic dystrophy. Its role in the development of vertebrate retinal cells, however, remains unknown. As an initial approach to its investigation, we have cloned three chick muscleblind genes, characterized their isoforms, and examined their expression patterns in the chick embryo retina. The relative levels of expression of the MBNL genes increased during embryonic development. In situ hybridization (ISH) showed that the three MBNL mRNAs had widespread patterns of expression at all the developmental stages examined. Of interest, the temporal and spatial patterns of protein expression, detected by immunocytochemistry with antibodies against MBNL1 and MBNL2, were much more restricted than those seen by ISH. At early stages (ED5-7), for example, MBNL1 and MBNL2 mRNAs were present throughout the retina, but immunoreactivity for the corresponding proteins was largely restricted to the periphery of the optic cup (presumptive iris/ciliary epithelium/ciliary margin zone). MBNL1 and MBNL2 immunoreactivity became detectable at the fundus at later stages, but was limited to a very small subset of the cells that had ISH signals for the cognate mRNAs (particularly ganglion cells and photoreceptors). Within photoreceptors, MBNL1 and MBNL2 immunoreactivity first appeared in their inner segments; MBNL2 remained there, but MBNL1 became subsequently localized to their synaptic terminals. These expression patterns are consistent with the possibility that MBNLs may regulate photoreceptor development in the chick retina, much as MBL does in Drosophila, and suggest that the expression of MBNL1 and MBNL2 may be regulated posttranscriptionally.

A single application of cyclic loading can accelerate matrix deposition and enhance the properties of tissue-engineered cartilage

OBJECTIVE

Mechanical stimulation is a widely used method to enhance the formation and properties of tissue-engineered cartilage. While studies have evaluated the responsiveness of chondrocytes to mechanical stimuli, little is known about how much stimulation is actually required. Thus, the purpose of this study was to investigate the effect of a single application of cyclic loading to chondrocytes on the formation and properties of in vitro-formed tissue.

DESIGN

Isolated bovine articular chondrocytes were seeded on ceramic substrates in 3D culture and subjected to a single application of compressive cyclic loading at 1, 8 or 15 days after seeding. Once the time at which the chondrocytes were most sensitive to mechanical loading was determined, the effect of a single application on the synthesis and accumulation of matrix molecules as well as the mechanical properties of the in vitro-formed cartilage tissue was evaluated.

RESULTS

Chondrocytes were more responsive to cyclic loading applied early in culture. Cyclic forces applied 24 h after the cultures were established increased collagen and proteoglycan syntheses (48 +/- 11% and 49 +/- 11%, respectively). This single application of cyclic loading also increased the accumulation of collagen (stimulated: 207 +/- 20 microg, control: 173 +/- 9 microg) and proteoglycans (stimulated: 302 +/- 24 microg, control: 270 +/- 14 microg) as well as improved the mechanical properties of the in vitro-formed tissue (twofold increase in equilibrium stress and modulus) determined 4 weeks after the applied stimulus.

CONCLUSIONS

A single application of cyclic loading to chondrocytes early in culture increased matrix accumulation and enhanced the mechanical properties of the in vitro-formed tissue. This suggests that mechanical forces do not have to be applied intermittently over long periods of time to accelerate in vitro tissue formation.

Cellular invasion of the chicken corneal stroma during development: regulation by multiple matrix metalloproteases and the lens

Avian corneal development requires cellular invasion into the acellular matrix of the primary stroma. Previous results show that this invasion is preceded by the removal of the fibril-associated type IX collagen, which possibly stabilizes matrices through interfibrillar cross-bridges secured by covalent crosslinks. In the present study, we provide evidence for the expression of three matrix metalloproteinases (MMPs) in early corneas, two of which act cooperatively to selectively remove type IX collagen in situ. In organ cultures, MMP inhibitors (either TIMP-2 or a synthetic inhibitor) resulted in arrested development, in which collagen IX persisted, and the stroma remained compact and acellular. We also show that blocking covalent crosslinking of collagen allows for cellular invasion to occur, even when the removal of type IX collagen is prevented. Thus, one factor regulating corneal invasion is the physical structure of the matrix, which can be modified by either selective proteolysis or reducing interfibrillar cross-bridges. We also detected another level of regulation of cellular invasion involving inhibition by the underlying lens. This block, which seems to influence invasive behavior independently of matrix modification, is a transient event that is released in ovo just before invasion proceeds.

Characterization of recombinant amino-terminal NC4 domain of human collagen IX: interaction with glycosaminoglycans and cartilage oligomeric matrix protein

The N-terminal NC4 domain of collagen IX is a globular structure projecting away from the surface of the cartilage collagen fibril. Several interactions have been suggested for this domain, reflecting its location and its characteristic high isoelectric point. In an attempt to characterize the NC4 domain in more detail, we set up a prokaryotic expression system to produce the domain. The purified 27.5-kDa product was analyzed for its glycosaminoglycan-binding potential by surface plasmon resonance and solid-state assays. The results show that the NC4 domain of collagen IX specifically binds heparin with a K(d) of 0.6 microm, and the full-length recombinant collagen IX has an even stronger interaction with heparin, with an apparent K(d) of 3.6 nm. The heparin-binding site of the NC4 domain was located in the extreme N terminus, containing a heparin-binding consensus sequence, whereas electron microscopy suggested the presence of at least three additional heparin-binding sites on full-length collagen IX. The NC4 domain was also shown to bind cartilage oligomeric matrix protein. This interaction and the association of cartilage oligomeric matrix protein with other regions of collagen IX were found to be heparin-competitive. Circular dichroism analyses of the NC4 domain indicated the presence of stabilizing disulfide bonds and a thermal denaturation point of about 80 degrees C. The pattern of disulfide bond formation within the NC4 domain was identified by tryptic peptide mass mapping of the NC4 in native and reduced states. A similar pattern was demonstrated for the NC4 domain of full-length recombinant collagen IX.

The homeobox gene Six3 is a potential regulator of anterior segment formation in the chick eye

The anterior segment of the vertebrate eye consists of highly organized and specialized ocular tissues critical for normal vision. The periocular mesenchyme, originating from the neural crest, contributes extensively to the anterior segment. During chick eye morphogenesis, the homeobox gene Six3 is expressed in a subset of periocular mesenchymal cells and in differentiating anterior segment tissues. Retrovirus-mediated misexpression of Six3 causes eye anterior segment malformation, including corneal protrusion and opacification, ciliary body and iris hypoplasia, and trabecular meshwork dysgenesis. Histological and molecular marker analyses demonstrate that Six3 misexpression disrupts the integrity of the corneal endothelium and the expression of extracellular matrix components critical for corneal transparency. Six3 misexpression also leads to a reduction of the periocular mesenchymal cell population expressing Lmx1b, Pitx2, and Pax6, transcription factors critical for eye anterior segment morphogenesis. Moreover, elevated levels of Six3 attenuate proliferation of periocular mesenchymal cells in vitro and differentiating anterior segment tissues in vivo. These results suggest that, in addition to its function in eye primordium determination, Six3 plays a role in regulating the development of the vertebrate eye anterior segment.

Collagen-binding domain of a Clostridium histolyticum collagenase exhibits a broad substrate spectrum both in vitro and in vivo

The substrate spectrum of the tandem collagen-binding domain (CBD) of Clostridium histolyticumclass I collagenase (ColG) was examined both in vitro and in vivo. CBD bound to insoluble type I, II, III and IV collagens in vitro, and to skin, aorta, tendon, kidney, trachea and corneal tissues containing various types of collagen fibrils or sheets. CBD bound to all kinds of collagen fibrils regardless of their diameters and also bound to sheet-forming collagen in the glomerular basal lamina or Descemet's membrane of the cornea. This wide substrate spectrum expands possible applications of the drug delivery system we proposed previously (PNAS 95:7018-7023, 1998). Therapeutic agents fused with CBD will bind not only to subcutaneous tissues, but also to other tissues containing non-type I collagen.

Age-dependent changes in the expression of matrix components in the mouse eye

Although the presence of 'cartilage-specific' collagens in the eye has been documented earlier, very little is known about their synthesis rates during ocular development, growth and aging. The purpose of the present study was to follow changes in the mRNA levels and distribution of key components of the extracellular matrix in the eyes of normal and transgenic Del1 mice, harboring a short deletion mutation in the type II collagen gene, during ocular growth and aging. Total RNAs extracted from mouse eyes were studied by Northern analysis for mRNA levels of type I, II, III, VI, IX and XI collagens, biglycan, fibromodulin and decorin. A predominant finding of the present study was the marked reduction in the mRNA levels of type I and II collagens in the eye upon aging. The changes in the mRNA levels of type III and VI collagen and proteoglycans were smaller. Localization of type II and IX collagen in the eye was performed by immunohistochemistry. Despite the reduction in the type II collagen mRNA levels, immunohistochemistry confirmed widespread distribution of the protein also in aging mouse eyes, suggesting its slow turnover. Although the Del1 mutation caused gradual degenerative lesions in the eyes, the distribution of the protein remained essentially unchanged. The widespread distribution and marked downregulation of type II collagen production in the mouse eye upon aging probably explain the gradual development of degenerative lesions, particularly in the eyes of transgenic Del1 mice, where production of mutant type II collagen chains also contributes to the process.

Axial structure of the heterotypic collagen fibrils of vitreous humour and cartilage

We have compared the axial structures of negatively stained heterotypic, type II collagen-containing fibrils with computer-generated staining patterns. Theoretical negative-staining patterns were created based upon the "bulkiness" of the individual amino acid side-chains in the primary sequence and the D-staggered arrangement of the triple-helices. The theoretical staining pattern of type II collagen was compared and cross-correlated with the experimental staining pattern of both reconstituted type II collagen fibrils, and fibrils isolated from adult and foetal cartilage and vitreous humour. The isolated fibrils differ markedly in both diameter and composition. Correlations were significantly improved when a degree of theoretical hydroxylysine glycosylation was applied, showing for the first time that this type of glycosylation influences the negative-staining pattern of collagen fibrils. Increased correlations were obtained when contributions from types V/XI and IX collagen were included in the simulation model. The N-propeptide of collagen type V/XI and the NC2 domain of type IX collagen both contribute to prominent stain-excluding peaks in the gap region. With decreasing fibril diameter, an increase of these two peaks was observed. Simulations of the fibril-derived staining patterns with theoretical patterns composed of proportions of types II, V/XI and IX collagen confirmed that the thinnest fibrils (i.e. vitreous humour collagen fibrils) have the highest minor collagen content. Comparison of the staining patterns showed that the organisation of collagen molecules within vitreous humour and cartilage fibrils is identical. The simulation model for vitreous humour, however, did not account for all stain-excluding mass observed in the staining pattern; this additional mass may be accounted for by collagen-associated macromolecules.

A short isoform of Col9a1 supports alveolar bone repair

Bone wound created in intramembranous alveolar bone heals without the formation of cartilage precursor tissue. However, the expression of cartilage collagen mRNAs has been suggested. In this report, we examined the expression and the potential role of type IX collagen in bone restoration and remodeling. The sequence specific polymerase chain reaction demonstrated the exclusive expression of short transcriptional isoform of alpha1(IX) collagen (Col9a1) in alveolar bone wound healing, while the long isoform of Col9a1 transcript was absent. Type IX collagen was immunolocalized in the preliminary matrix organized in granulation tissue before trabecular bone formation in tooth extraction socket. In Col9a1-null mutant mice, there were considerable variations in alveolar bone wound healing with the absence of or abnormally organized trabecular bone. Occasionally, unusual apposition of cortical-bone-like layers in bone marrow space was observed. The Col9a1-null mice indicated no growth retardation, and their facial and long bones maintained the normal size and shape. However, the primary spongiosa region of adult Col9a1 mutant mice showed an abnormal trabecular bone structure associated with abnormal immunostaining with the hypertrophic cartilage specific type X collagen antibody. These data suggest that type IX collagen short transcriptional variant is involved in the restoration and remodeling processes of trabecular bone.

Collagen in tissue-engineered cartilage: types, structure, and crosslinks

The function of articular cartilage as a weight-bearing tissue depends on the specific arrangement of collagen types II and IX into a three-dimensional organized collagen network that can balance the swelling pressure of the proteoglycan/water gel. To determine whether cartilage engineered in vitro contains a functional collagen network, chondrocyte-polymer constructs were cultured for up to 6 weeks and analyzed with respect to the composition and ultrastructure of collagen by using biochemical and immunochemical methods and scanning electron microscopy. Total collagen content and the concentration of pyridinium crosslinks were significantly (57% and 70%, respectively) lower in tissue-engineered cartilage that in bovine calf articular cartilage. However, the fractions of collagen types II, IX, and X and the collagen network organization, density, and fibril diameter in engineered cartilage were not significantly different from those in natural articular cartilage. The implications of these findings for the field of tissue engineering are that differentiated chondrocytes are capable of forming a complex structure of collagen matrix in vitro, producing a tissue similar to natural articular cartilage on an ultrastructural scale.

Cartilage fibrils of mammals are biochemically heterogeneous: differential distribution of decorin and collagen IX

Cartilage fibrils contain collagen II as the major constituent, but the presence of additional components, minor collagens, and noncollagenous glycoproteins is thought to be crucial for modulating several fibril properties. We have examined the distribution of two fibril constituents-decorin and collagen IX-in samples of fibril fragments obtained after bovine cartilage homogenization. Decorin was preferentially associated with a population of thicker fibril fragments from adult articular cartilage, but was not present on the thinnest fibrils. The binding was specific for the gap regions of the fibrils, and depended on the decorin core protein. Collagen IX, by contrast, predominated in the population with the thinnest fibrils, and was scarce on wider fibrils. Double-labeling experiments demonstrated the coexistence of decorin and collagen IX in some fibrils of intermediate diameter, although most fibril fragments from adult cartilage were strongly positive for one component and lacked the other. Fibril fragments from fetal epiphyseal cartilage showed a different pattern, with decorin and collagen IX frequently colocalized on fragments of intermediate and large diameters. Hence, the presence of collagen IX was not exclusive for fibrils of small diameter. These results establish that articular cartilage fibrils are biochemically heterogeneous. Different populations of fibrils share collagen II, but have distinct compositions with respect to macromolecules defining their surface properties.

Collagen type IX and developmentally regulated swelling of the avian primary corneal stroma

A critical event in avian corneal development occurs when the acellular primary stroma swells and becomes populated by mesenchymal cells that migrate from the periphery. These cells then deposit the mature stromal matrix that exhibits the unique features necessary for corneal function. Our previous work correlated the disappearance of collagen type IX immunoreactivity at stage 27 (5 1/2-6 days) with matrix swelling and invasion. To investigate further the mechanism of this disappearance, we employed immunohistochemistry after tissue fixation with Histochoice, a non-crosslinking fixative, immunoblot analysis of protein extracts, and gel substrate chromatography (zymography) to detect endogenous proteolytic activity. We found that corneas fixed in Histochoice retain immunoreactivity for type IX collagen for 1-2 days after corneal swelling. This immunoreactivity, however, becomes extractable from tissue sections of unfixed corneas at the time of initiation of stromal swelling and mesenchymal cell invasion. Immunoblot analysis confirmed that, following swelling, immunoreactivity for collagen IX decreased substantially in corneas, but not in the vitreous body, which served as a comparison. Analysis of ammonium sulfate (AS) fractions of such extracts indicated that, at the time of swelling, much of the immunoreactivity for type IX collagen in cornea shifted from the AS precipitate (containing high molecular weight molecules) to the AS supernatant (containing smaller fragments). In contrast, collagen IX immunoreactivity from the vitreous was precipitated by ammonium sulfate throughout the period of study. Collagen type II, a major fibrillar collagen in both the corneal stroma and vitreous, remained in the high molecular weight fraction at all times examined. Zymography detected the presence of the latent (proenzyme) form of gelatinase A (MMP-2) before corneal swelling and invasion (4 days), and both the latent and active forms of the enzyme after corneal swelling. This suggests tissue-specific, developmentally regulated proteolysis of collagen IX as a trigger for corneal matrix swelling.

Use of rotary shadowing electron microscopy to investigate the collagen fibrils in the extracellular matrix of cuttle-fish (Sepia officinalis) and chicken cartilage

Collagen fibrils isolated from sternal cartilage of chick embryo and chondrocranium of cuttle-fish (Sepia officinalis) were examined with the electron microscope after rotary showing. The aim was to determine whether collagen fibrils from S. officinalis cartilage contained collagen molecules similar to the type IX collagen of vertebrate cartilage. Cartilage from both sources presented a highly variable appearance and only occasionally did preparations contain fibrils having the structure described by Vaughan et al. (1988) for vertebrate cartilage. Subsequent electron microscope investigation of collagen samples during the various stages of fibril preparation showed that the method did not yield reproducible results, and that is altered the morphology of the isolated structures. It was not, therefore, possible to confirm the hypothesis that collagen molecules with a morphology similar to that type IX vertebrate collagen are a component of the extracellular matrix of cephalopod cartilage.

Immunolocalization of type IX collagen in normal and spontaneously osteoarthritic canine tibial cartilage and isolated chondrons

OBJECTIVE

The pericellular localization of type IX collagen in avian and mammalian hyaline cartilages remains controversial, while its distribution during osteoarthritic degeneration is poorly understood. This study aimed to compare and contrast the immunohistochemical distribution of type IX collagen in normal mature and spontaneously osteoarthritic canine tibial cartilage.

DESIGN

Thick vibratome sectioning techniques were evaluated and compared with isolated chondrons using a range of streptavidin-linked probes in combination with light, confocal and transmission electron microscopy.

RESULTS

In normal intact samples, type IX collagen was concentrated in the pericellular microenvironment, while a weaker extracellular reaction around each chondron separated the territorial matrix from the unstained interterritorial matrix. Further differentiation was evident in isolated chondrons where the fibrous pericellular capsule stained more intensely than the tail and interconnecting segments between columnated chondrons. Two regions of type IX reactivity were identified in osteoarthritic tissue: an intensely stained superficial reactive region below the eroding margins, and normal deep layer cartilage where pericellular staining persists. The superficial reactive region was characterized by chondron swelling and chondrocyte cluster formation, a loss of pericellular type IX staining, and a significant increase in matrix staining between clusters. Disintegration and loss of fibrillar collagens was evident in both the swollen microenvironment and adjacent territorial matrices.

CONCLUSIONS

The results suggest that changes in type IX distribution, expansion of the pericellular microenvironment and chondrocyte proliferation represent key elements in the chondron remodeling and chondrocyte cluster formation associated with osteoarthritic degeneration.

The biomechanics of cartilage load-carriage

This paper presents a review and critical appraisal of the more recent attempts to understand the fundamental mechanisms of load-carriage in articular cartilage. In the first section the question is addressed as to how the intrinsic strength of the matrix is developed with respect to its ultrastructure. In the second part we examine various models proposed to explain the response of the matrix to externally applied compressive forces in terms of its unique physico-chemical properties.

Expression of chondroitin sulfate and keratan sulfate proteoglycans in the path of growing retinal axons in the developing chick

Previous investigations have identified proteoglycans in the central nervous system during development and have implicated some proteoglycans as axon guidance molecules that act by inhibiting axon extension. The present study investigated the pattern of immunoreactivity for several glycosaminoglycans common to certain proteoglycans relative to growing retinal axons in the developing chick visual system and in retinal explant cultures. Immunostaining for chondroitin-6-sulfate, chondroitin-4-sulfate, and keratan sulfate was observed to colocalize with retinal axons throughout the retinofugal pathway during the entire period of retinal axon growth. The proteoglycan form of collagen IX, however, was only observed in the retina, primarily peripheral to the areas with actively growing axons. The pattern of immunostaining for chondroitin sulfate in tissue sections suggested that the retinal axons might be a source for some of the chondroitin sulfate immunostaining in the developing visual pathway. This was confirmed in that chondroitin sulfate immunostaining was also observed on neurites emanating from cultured retinal explants. These findings indicate that retinal axons grow in the presence of chondroitin sulfate and keratan sulfate proteoglycans and that these proteoglycans in the developing chick visual pathway have functions other than to inhibit axon growth.

Chondrocyte differentiation

Data obtained while investigating growth plate chondrocyte differentiation during endochondral bone formation both in vivo and in vitro indicate that initial chondrogenesis depends on positional signaling mediated by selected homeobox-containing genes and soluble mediators. Continuation of the process strongly relies on interactions of the differentiating cells with the microenvironment, that is, other cells and extracellular matrix. Production of and response to different hormones and growth factors are observed at all times and autocrine and paracrine cell stimulations are key elements of the process. Particularly relevant is the role of the TGF-beta superfamily, and more specifically of the BMP subfamily. Other factors include retinoids, FGFs, GH, and IGFs, and perhaps transferrin. The influence of local microenvironment might also offer an acceptable settlement to the debate about whether hypertrophic chondrocytes convert to bone cells and live, or remain chondrocytes and die. We suggest that the ultimate fate of hypertrophic chondrocytes may be different at different microanatomical sites.

Analysis of transcriptional isoforms of collagen types IX, II, and I in the developing avian cornea by competitive polymerase chain reaction

The genes for the alpha 1(IX), alpha 1(II), and alpha 2(I) collagen chains can give rise to different isoforms of mRNA, generated by alternative promotor usage [for alpha 1(IX) and alpha 2(I)] or alternative splicing [for alpha 1(II)]. In this study, we employed competitive reverse transcriptase PCR to quantitate the amounts of transcriptional isoforms for these genes in the embryonic avian cornea from its inception (about 3 1/2 days of development) to 11 days. In order to compare values at different time points, the results were normalized to those obtained for the "housekeeping" enzyme, glycerol-3-phosphate dehydrogenase (G3PDH). These values were compared to those obtained from other tissues (anterior optic cup and cartilage) that synthesize different combinations of the collagen isoforms. We found that, in the cornea, transcripts from the upstream promotor of alpha 1(IX) collagen (termed "long IX") were predominant at stage 18-20 (about 3 1/2 days), but then fell rapidly, and remained at a low level. By 5 days (just before stromal swelling) the major mRNA isoform of alpha 1(IX) was from the downstream promoter (termed "short IX"). The relative amount of transcript for the short form of type IX collagen rose to a peak at about 6 days of development, and then declined. Throughout this period, the predominant transcriptional isoform of the collagen type II gene was IIA (i.e., containing the alternatively spliced exon 2). This indicates that the molecules of type II collagen that are assembled into heterotypic fibrils with type I collagen possess, at least transiently, an amino-terminal globular domain similar to that found in collagen types I, III, and V. For type I, the "bone/tendon" mRNA isoform of the alpha 2(I) collagen gene was predominant; transcripts from the downstream promotor were at basal levels. In other tissues expressing collagen types IX and II, long IX was expressed predominantly with the IIA form in the anterior optic cup at stage 22/23; in 14 1/2 day cartilage, long IX was expressed predominantly along with the IIB form of alpha 1(II). The downstream transcript of the alpha 2(I) gene (Icart) was found at high levels only in cartilage.

Cellular invasion and collagen type IX in the primary corneal stroma in vitro

During different stages in the development of the avian cornea, various collagen types have been shown to participate in matrix formation and have been implicated in morphogenesis. One of these is the fibril-associated collagen type IX. This molecule is present when the primary corneal stroma is in a compact state, but rapidly disappears just prior to stromal swelling and its invasion by mesenchymal cells. The temporospatial pattern of the disappearance of type IX collagen in the developing cornea suggests that this molecule may be involved in stabilizing the primary corneal stromal matrix by interacting either with other type IX collagen molecules or with other matrix components. To explore further whether the removal of type IX collagen is involved in stromal swelling, we have employed an in vitro culture system in which swelling of the primary stroma and mesenchymal cell invasion can be experimentally manipulated by culturing chick corneal explants on a Nuclepore filter support in the presence or absence of an associated lens. We have also examined the effect of exogenously added human recombinant tissue inhibitor of metalloproteinases (TIMP-1) on the presence of type IX collagen and cellular invasion. When stage 25-26+ corneal explants were cultured with an associated lens, the primary stroma did not swell; immunohistochemically detectable type IX collagen was still present, and mesenchymal cell invasion failed to occur. Conversely, when the same stages of corneal explants were cultured without an associated lens, the primary stroma swelled; type IX collagen disappeared, and mesenchymal cell migration occurred. Under both conditions, however, the type II collagen of the stroma, which is known to be a component of the striated fibrils, remained clearly detectable and with time even seemed to increase in amount. This result is consistent with the proposition that type IX collagen is one factor involved in maintaining the primary stroma as a compact matrix, possibly by functioning as a bridging/stabilizing factor. When TIMP was added to cultures of corneal explants, type IX collagen remained detectable in focal regions, suggesting that one or more metalloproteinases are involved in the removal of the type IX collagen. In addition, some of these type IX-containing regions contained mesenchymal cells, suggesting that in addition to type IX collagen other factors are likely to be involved in regulating mesenchymal cell migration.

Immunization with undenatured bovine zonular fibrils results in monoclonal antibodies to fibrillin

Microfibrils were dissected from the zonular apparatus of the bovine eye, homogenized and used as an immunogen to prepare monoclonal antibodies. Initial screening of hybridomas was performed by immunoblotting to a sonicate of zonular fibrils and by immunolocalization to frozen sections of the zonular apparatus. Subsequently, monoclonal antibodies with strong immunoreactivity to zonular fibrils were shown to recognize microfibrils in a wide range of connective tissues both by immunofluorescent staining and by electron microscopic immunolocalization. All antibodies were found to recognize a single protein of 350 kDa on Western blotting of the proteins secreted by bovine aortic smooth muscle cells. A protein of the same molecular weight and properties was recognized by an antibody previously prepared by another group against fibrillin. A member of the fibrillin family therefore represents the major immunogen of intact zonular fibrils, and the results support previous evidence for a close relationship between zonular fibrils and other connective tissue microfibrils. The zonular apparatus is a suitable system to obtain purified preparations of microfibrils in order to investigate their composition and structural organization.

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.

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)

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.

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)

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.

The application of scanning confocal microscopy in cartilage research

Scanning confocal microscopy has been used in conjunction with immunofluorescent localization to address two areas of debate in cartilage research. With the enhanced resolution and optical sectioning capability of this new technique, we have demonstrated that type IX collagen is preferentially located in an area around the chondrocyte, even in young cartilage. We have also shown that cathepsin B production is not confined to de-differentiated chondrocytes. The advantages and versatility of scanning confocal microscopy have thus clearly been demonstrated.

Conformational epitopes on interstitial collagens

The antigenic response to the helical domain of collagens is normally very low, with the nature of the epitopes recognized by antibodies being dependent on the species of origin. Thus, in certain species, for example rabbit, sequential determinants on single alpha-chains are found, whereas in other species such as mouse, conformational epitopes are predominant. A variety of techniques for identification of epitopes, including rotary shadowing, examination of specific fragments and chemical modification reactions are discussed. The application of these techniques is illustrated using a range of monoclonal antibodies to interstitial collagens. These antibodies show that epitopes are distributed over the length of the collagen molecule.

Rotary shadowing of elastic system microfibrils in the ocular zonule, vitreous, and ligamentum nuchae

Rotary shadowing of zonular fibrils in human and bovine eyes revealed a "string of beads" configuration with multiple interconnecting filaments, identical to that recently reported in fibrils of unknown type within the vitreous. These 29 nm beaded fibrils were the only macrostructures present in zonular samples, showing ultrastructural features correlating with both the macro and microperiodicity of zonular fibrils in tissues. Interbead periodicity varied from 30-57 nm and interbead filaments appeared capable of stretching even further, possibly explaining the inherent elasticity of zonular fibrils. The junctions between outer filaments and beads were fibrillin-positive. Similar beaded fibrils were found in the human and bovine anterior vitreous along with type II and IX collagen fibrils, proteoglycan filaments and other unidentified fibrils. After collagenase and elastase digestion, bovine ligamentum nuchae showed type VI collagen fibrils and clumps of beaded fibrils like those in zonule and vitreous. This distribution indicates that the beaded fibril is the microfibril which constitutes the basic unit of the elastic system.

Developmental expression of genes in chick growth cartilage detected by in situ hybridization

We have used in situ hybridization to examine expression of collagen type I, II, and X mRNA and osteonectin mRNA in the chick epiphysis. Tissue samples from the proximal tibial growth cartilage were fixed in modified Carnoy's solution, dehydrated in ethanol, and embedded in paraffin. Longitudinal and transverse sections were demineralized with HCl and digested with hyaluronidase and proteinase K. In situ hybridization was carried out using biotinylated cDNA probes; the hybridized probe was detected using a streptavidin-biotinylated alkaline phosphatase conjugate. This procedure permitted detection of the corresponding mRNAs in cartilage with high sensitivity and low background. Osteonectin mRNA was detected in proliferating cartilage; lower levels of osteonectin mRNA were seen in the mid-hypertrophic region. This mRNA species was also expressed in cells that border the vascular canals in the premineralized region of the epiphysis. Collagen type X mRNA was detected throughout the hypertrophic zone. As localization of collagen type X mRNA corresponded to the site of maximal synthesis of the protein, reported in other studies, our results would further support the suggestion that this protein is associated with mineralization of cartilage. Collagen type II mRNA was seen in both the proliferating and the hypertrophic regions of the cartilage. Highest levels of expression were observed in the proliferative region. The results suggest that the transcriptional control of collagen type II and X by cells of the proliferating and hypertrophic regions of the growth cartilage may be related.

Widespread distribution of type II collagen during embryonic chick development

Type II collagen is a major component of hyaline cartilage, and has been suggested to be causally involved in promoting chondrogenesis during embryonic development. In the present study we have performed an immunohistochemical analysis of the distribution of type II collagen during several early stages of embryonic chick development. Unexpectedly, we have found that type II collagen is widely distributed in a temporally and spatially regulated fashion in basement membranes throughout the trunk of the embryo at stages 14 through 19, including regions with no apparent relationship to chondrogenesis. Immunohistochemical staining with two different monoclonal antibodies against type II collagen, as well as with an affinity-purified polyclonal antibody, is detectable in the basement membranes of the neural tube, notochord, auditory vesicle, dorsal/lateral surface ectoderm, lateral/ventral gut endoderm, mesonephric duct, and basal surface of the splanchnic mesoderm subjacent to the dorsal aorta, and at the interface between the epimyocardium and endocardium of the developing heart. In contrast, immunoreactive type IX collagen is detectable only in the perinotochordal sheath in the trunk of the embryo at these stages of development. Thus type II collagen is much more widely distributed during early development than previously thought, and may be fulfilling some as yet undefined function, unrelated to chondrogenesis, during early embryogenesis.

The three-dimensional 'knit' of collagen fibrils in articular cartilage

TEM stereoscopy of thick sections has been used to reconstruct the 3-dimensional relationships of collagen fibrils in the general matrix of articular cartilage in its relaxed and deformed states. As well as identifying a variety of fibril interactions involving direct physical entwinement which are assumed to provide matrix cohesion the study also highlights the functional importance of the repeatedly kinked morphology exhibited by the radial fibrils. It is suggested that these fibril kinks, in accommodating local compressive strains that approach 100%, function as macro-molecular hinges and permit the collagen elements to undergo large spatial rearrangement without risk to their structural integrity.

A histochemical localization on Maclura pomifera lectin during osteogenesis

Mandibular condyles of 4-week-old Wistar strain rats and mandibles of ICR strain mice from 14 days gestation stage to 2 days postnatal stage were used to investigate the localization of Maclura pomifera lectin (MPA) during two modes of osteogenesis. During endochondral ossification of the mandibular condyle, MPA was only localized at the peripheral regions of calcified cartilage after the destruction of chondrocyte lacunae. Bone extracellular matrix (ECM) was not reacted with MPA. In intramembranous ossification of mice mandibles, MPA was stained intensively in the early bone ECM. The intensity of the MPA reaction decreased during bone development. In both cases of osteogenesis, chondroclasts and osteoclasts showed the strong affinity to MPA. These results indicated that the time- and position-specific changes within ECM proceeded during osteogenesis and that MPA was the useful probe to detect chondroclasts and osteoclasts.

Problems in the immunolocalization of type IX collagen in fetal calf cartilage using a monoclonal antibody

Monoclonal antibodies were prepared against the pepsin-resistant fragments (X1-X3) of bovine type IX collagen. One of the five hybridomas that gave a positive reaction in an enzyme-linked immunosorbent assay was selected (H1a) for structural analysis and immunolocalization of type IX collagen. The location of the epitope for H1a was deducted from immunoblots and electron microscopic observations after rotary shadowing. The H1a antibody binds to one end of the longest X2, X3, X4 molecules, and preferentially 40-55nm from one end of X1 molecules thus, on or near the noncollagenous domain, NC2. Different immunolocalizations of type IX collagen in the superficial, middle and deep zones of fetal calf epiphyseal cartilage were observed depending on the thickness of the section and on hyaluronidase digestion conditions. In the middle and deep zones, staining with H1a throughout the matrix was obtained only with thin sections (5 microns) and digestion for 1 h at 37 degrees C. With thick sections (15 microns) or with digestion for 1 h at 24 degrees C, staining was restricted to the pericellular regions. Staining throughout the matrix was obtained in the superficial zone under all experimental conditions. Without hyaluronidase treatment, no immunofluorescent staining was seen with either H1a or polyclonal antibody to type II collagen, indicating that type IX collagen is present throughout the matrix in the different zones of fetal calf cartilage. This result is in good accordance with the recent demonstration of common cross-links between type II and type IX collagen in chicken and bovine cartilage. However, the preferential unmasking of type IX collagen antigenic sites in the pericellular regions of middle and deep zones of fetal calf cartilage does not preclude the presence in that region of a special pericellular organization of the collagenous network.