Collagen genes and inherited connective tissue disease

Comparative ultrastructural localization of collagen types III, IV, VI and laminin in rat uterus and kidney

Antibodies against collagen types III and VI have been localized by electron immunohistochemistry with two different techniques in normal rat uterus and kidney. Antibodies directed against two components of the extracellular matrix with known localization, laminin and type IV collagen, were used as controls for the specificity of the localization. The results demonstrate that types III and VI are found in the interstitium as fine (10- to 15-nm), beaded fibrils and filaments (6- to 10-nm), respectively. Both are often found associated with thick, crossbanded type I collagen fibers (30- to 35-nm) and occasionally associated with some basement membranes adjacent to the interstitium. Further, the findings suggest that collagens III and VI may connect the various components of the extracellular matrix, such as type I fibers with basement membranes and other structures, thus forming an integrated functional unit.

Type I procollagen in the severe non-lethal form of osteogenesis imperfecta. Defective pro-alpha 1(I) chains in a patient with abnormal proteoglycan metabolism and mineral deposits in the dermis

We have screened type I procollagen synthesized in vitro by skin fibroblasts from several patients with the severe non-lethal form of osteogenesis imperfecta. Cells from one patient synthesized and secreted both normal and a larger amount of abnormal type I procollagen. The abnormal alpha chains are larger in size due to post-translational overmodifications involving the whole triple helical domain. Abnormal collagen heterotrimers had a melting temperature 2.5 degrees-3 degrees C lower than normal ones or from controls. Chemical analysis of collagen in the medium showed a greater degree of both lysyl hydroxylation and hydroxylysyl glycosylation, the major increase in molecular mass of overmodified alpha chains being due to the higher hydroxylysine-bound hexose content. The proband's cells modify proteoglycan metabolism and mineral crystals form in the dermis, possibly a response to abnormal collagen-proteoglycan interactions. These findings can be explained by a small defect in the product of one allele for pro-alpha 1(I) chains: three-quarters of the synthesized type I procollagen molecules are composed of trimers containing one or two chains defective near the C-terminus of the triple helix or in the C-propeptide. The data obtained for this patient confirmed that the severity of clinical manifestations in osteogenesis imperfecta strongly depends on the location and nature of the mutations, and that the phenotype could be a consequence of a collagen defect(s) and its influence on collagen-collagen interactions and collagen interactions with other connective tissue components.

Desmoplastic reaction of gastric carcinoma: a light- and electron-microscopic immunohistochemical analysis using collagen type-specific antibodies

The desmoplastic reaction in ten cases of gastric carcinoma was investigated light and electron immunohistochemically by using monospecific antibodies to collagen types. In addition to type I and III collagens, type V collagen was constantly recognized in the fibrous stroma, increasingly of the scirrhous carcinoma. Type IV collagen delineated the basement membranes of carcinoma nests linearly with occasional discontinuity, whereas in the scirrhous carcinoma, it was present along the thick bundles of collagenous fibers. Immunoelectron microscopic studies revealed that type I and III collagens were distributed on the collagen fibers, and type V collagen was stained in the margin of these fibers. These antibodies also reacted in the rough endoplasmic reticulum of fibroblasts or myofibroblasts in a few cases. Type IV collagen was localized in the periphery of smooth muscle cells, endothelial cells of collapsed capillaries, and myofibroblasts scattered in the stroma of scirrhous carcinoma. Carcinoma cells were not reactive with any antibodies examined. These findings suggest that type V collagen, as well as type I and III collagens, is involved in the formation of desmoplastic stroma, and that these collagens are reactively synthesized by fibroblasts and myofibroblasts in some interaction with invading carcinoma cells.

Cardiac anomalies in Williams-Beuren syndrome

We have described some of the cardiological findings in 66 patients with Williams-Beuren syndrome and analysed the two dimensional cross sectional echocardiograms in 61 of them in comparison with normal controls. Supravalvar aortic narrowing was shown in all patients examined echocardiographically and may be a useful diagnostic sign. We documented a 7.8% incidence of systemic hypertension, a 15% clinical and echocardiographic incidence of mitral valve prolapse, and a 11.6% incidence of bicuspid aortic valve.

Dysmorphic syndromes with demonstrable biochemical abnormalities

Many inborn errors of metabolism are associated with dysmorphic manifestations. In this review, we have attempted to correlate the dysmorphic features with the underlying metabolic defect or its consequences. Most of the defects which we have discussed affect the synthesis or degradation of macromolecules (for example, collagen, elastin, bone mineral, proteoglycans, glycoproteins, and triglycerides). Such defects may affect either a single enzyme or multiple enzymes in specific organelles, such as lysosomes or peroxisomes, or they may affect hormonal control of synthesis and degradation. Examples are also included of defects affecting the catabolism of simple molecules when accumulating metabolites have a secondary effect on macromolecules, as in homocystinuria. In a number of instances, however, the correlation between the biochemical abnormality and the dysmorphic features are not understood. Ultimately, all dysmorphic syndromes will be attributable to a biochemical defect or its effects. The aim of this overview is to provide an insight into the relationship between the two at the present time.

Structure of a full-length cDNA clone for the prepro alpha 2(I) chain of human type I procollagen. Comparison with the chicken gene confirms unusual patterns of gene conservation

A cDNA clone from a human placental library was found to consist of an essentially full-length cDNA of 4.6 kb for the prepro alpha 2(I) chain of type I procollagen. Nucleotide sequencing of the 5'-end of the cDNA provided a sequence of 1617 nucleotide residues and codons for 539 amino acid residues not previously defined. Comparison of the complete structure of the prepro alpha 2(I) cDNA with previously reported sequences for the chicken pro alpha 2(I) gene indicated that 83% of 1366 total amino acid residues were conserved. In the alpha-chain domain 84% of 1014 amino acid residues were conserved. Also, there was conservation of the previously noted preference for U and C in the third position of codons for glycine, proline and alanine. One major difference between the human and the chicken prepro alpha 2(I) chain was that the human chain contained 21 fewer proline residues, an observation that probably explains why the triple helix of human type I procollagen unfolds at temperatures that are 1-2 degrees C lower. In parallel experiments, sequencing of intron-exon boundaries for nine exons of genomic subclones confirmed and extended previous observations that the pro alpha 2(I) gene, like other genes from fibrillar collagens, has an unusual 54-base pattern of exon sizes that is highly conserved through evolution.

Perinatal lethal osteogenesis imperfecta in transgenic mice bearing an engineered mutant pro-alpha 1(I) collagen gene

Substitutions of single glycine residues of alpha 1(I) collagen have previously been associated with the inherited disease osteogenesis imperfecta type II. Transgenic mice bearing a mutant alpha 1(I) collagen gene into which specific glycine substitutions have been engineered show a dominant lethal phenotype characteristic of the human disease, and demonstrate that as little as 10% mutant gene expression can disrupt normal collagen function.

Linkage disequilibrium analyses and restriction mapping of four RFLPs at the pro alpha 2(I) collagen locus: lack of correlation between linkage disequilibrium and physical distance

Restriction fragment length polymorphisms (RRLPs) located at short distances may demonstrate linkage disequilibrium. Under the assumption that the distances between the loci of the RFLPs are inversely related to the linkage disequilibria, gene order may be deduced. However, if the assumption is invalid, the results may be incorrect. We have studied four different DNA polymorphisms at the COLIA2 locus in 180 unrelated Norwegian individuals. Observed frequencies (presence/absence) for the different polymorphic sites were as follows: site A (EcoRI) 0.30/0.70, site B (MspI) 0.83/0.16, site C (StuI) 0.86/0.14, and site D (RsaI) 0.66/0.34. Of 16 possible haplotypes 12 were demonstrated, and 2 additional were deduced to be present. Restriction mapping of the four polymorphic sites gave the following order of the sites from the 5' to the 3' of the gene: A-D-B-C. Linkage disequilibrium was not found between the sites A and D; strong disequilibrium was found between sites A and C, and B and C; and less strong, between A and B, B and D, and C and D. Analysis of linkage disequilibrium coefficients between all pairs of loci demonstrated that there is no consistent relationship between linkage disequilibrium and physical distance (tau = -0.07). These results suggest that for a small region of the genome, factors such as deviating mutation rate and gene conversion may add significantly to rearrangements by recombination. Thus, a deduced gene order from linkage disequilibrium data has to be regarded with great caution.

Comparative studies of collagens in normal and keratoconus corneas

In this paper we present strong evidence that the aberrations in keratoconus corneas are not directly related to alterations in collagen composition and distribution. This conclusion is based on comparative studies of collagen types I, III, IV, V and the recently described collagen types VI and VII in keratoconus and normal corneas. The data are derived from biochemical analysis of collagen fractions sequentially extracted with pepsin and sodium-dodecylsulphate, from amino acid analysis of hydrolysates of entire corneal tissues as well as from immunoblotting of the extracted collagens with specific antibodies. These antibodies were also used to examine the distribution of the collagens in immunofluorescence experiments on corneal sections. The yields of the collagen extractions were demonstrated to be age dependent but were not altered in keratoconus samples. Apart from one case associated with osteogenesis imperfecta type I, comparative studies of keratoconus and normal corneas showed no differences in collagen composition of the extracts. This was confirmed by amino acid analysis of tissue-hydrolysates. The distributions of collagen types I, III, IV, V, VI and VII in corneal sections were in general unchanged in keratoconus corneas, the only differences being in scar tissues observed in the Bowman layer of some keratoconus samples.

Kniest dysplasia is characterized by an apparent abnormal processing of the C-propeptide of type II cartilage collagen resulting in imperfect fibril assembly

Epiphyseal and growth plate cartilages from four cases of Kniest dysplasia have been studied. In each case collagen fibril organization appeared abnormal by electron microscopy compared with age-matched normal cartilages: fibrils were much thinner, of irregular shape and did not exhibit the characteristic banding pattern. This was associated with the absence (compared with normal cartilage) of the C-propeptide of type II collagen (chondrocalcin) from the extracellular matrix of epiphyseal cartilages, although it was detected (as in normal cartilages) in the lower hypertrophic zone of the growth plate in association with calcifying cartilage. The C-propeptide was abnormally concentrated in intracellular vacuolar sites in Kniest cartilages and its total content was reduced in all cases but not in all cartilages. Moreover, it was not a part of the procollagen molecule. In contrast, type II collagen alpha-chain size was normal, indicating the formation of a triple helix. Also type II collagen content was normal and it was present in extracellular sites and only occasionally detected intracellularly. These observations suggest that the defect in Kniest dysplasia may result from the secretion of type II procollagen lacking the C-propeptide and abnormal fibril formation, and that the C-propeptide is normally required for fibril formation.

Osteogenesis imperfecta

Major advances have occurred in the classification of OI and in the definition of underlying molecular defects. A clearer understanding of the pathogenesis of OI and of the relationships between the phenotypes and genotypes should emerge. The study of induced mutations in selected regions of the collagen genes with expression in cultured cells or transgenic mice should hasten this process. These advances will also provide a basis for studies into the large number of other genetically determined connective tissue disorders that are grouped together as the skeletal dysplasias. The results of recent studies in OI are providing a unique insight into many aspects of collagen and connective tissue biochemistry, physiology and pathology.

Determination of the single polyadenylation site of the human pro alpha 1(II) collagen gene

Several cDNA clones for the human type II procollagen mRNA were isolated from a cartilage cDNA library. Six of the clones containing the longest inserts were subjected to restriction site mapping for alignment. All these six clones extended to the poly A tail. The longest clone, containing a 1470 bp insert, was named pHCAR3. Sequencing of pHCAR3 made it clear that neither of the two canonical AATAAA sequences of the human type II collagen gene is used as the polyadenylation signal. Two 60 bp stretches of high interspecies homology terminating in a hexanucleotide ATTAAA, located 23 nucleotides upstream of the poly A tail, apparently have an important role in determining the single polyadenylation signal for this gene. S1 protection experiments confirmed these observations.

Glycosaminoglycan-free small proteoglycan core protein is secreted by fibroblasts from a patient with a syndrome resembling progeroid

A male patient, 4 years 9 mo old and having progeroidal appearance, exhibited delayed mental development and multiple abnormalities of connective tissues including growth failure, osteopenia of all and dysplasia of some bones, defective deciduous teeth, loose but elastic skin, delayed wound healing with formation of thin atrophic scars, scanty scalp hair, hypotonic muscles, and hypermobile joints. Skin fibroblasts of the patient converted only about half of the core protein of the small proteodermatan sulfate to a mature glycosaminoglycan chain-bearing proteoglycan. The remaining core protein, which contained complex-type asparagine-bound oligosaccharides, was secreted with almost normal kinetics. Xylosyltransferase activity and the synthesis of other proteoglycan types were normal. Normal induction of glycosaminoglycan synthesis occurred in the presence of 1 mM, but there was very little induction in the presence of 0.01 mM p-nitrophenyl-beta-xyloside. An antibody against an N-terminal pentadecapeptide of the core protein recognized the glycosaminoglycan-free core protein from the patient less well than the chain-bearing protein treated with chondroitin ABC lyase. Though these results do not define the basic defect unambiguously, they provide the first report of a disorder being due to an abnormality in small proteoglycan biosynthesis.

The human alpha 2(IV) collagen gene, COL4A2, is syntenic with the alpha 1(IV) gene, COL4A1, on chromosome 13

We have previously assigned the gene for the alpha 1 chain of type IV collagen to chromosome 13. In this report we show that the gene coding for the second chain of this heterotrimer is on the same chromosome. This is the first example of the genes for both chains of one collagen molecule being syntenic.

Tissue-specific expression of the human type II collagen gene in mice

Type II collagen is crucial to the development of form in vertebrates as it is the major protein of cartilage. To study the factors regulating its expression we introduced a cosmid containing the human type II collagen gene, including 4.5 kilobases of 5' and 2.2 kilobases of 3' flanking DNA, into embryonic stem cells in vitro. The transformed cells contribute to all tissues in chimeric mice allowing the expression of the exogenous gene to be studied in vivo. Human type II collagen mRNA is restricted to tissues showing transcription from the endogenous gene and human type II collagen is found in extracellular matrix surrounding chondrocytes in cartilage. The results indicate that the cis-acting requirements for correct temporal and spatial regulation of the gene are contained within the introduced DNA.

Biosynthetic precursors of cartilage chondroitin sulfate proteoglycan

Early steps in the biosynthesis of chondroitin sulfate proteoglycan (CSPG) and collagenous cartilage matrix molecules were examined by the comparison of products translated in mRNA-directed cell-free reactions and those synthesized by intact cartilage cells. RNA isolated from embryonic chicken sterna was used to direct cell-free translation reactions. Chicken sternal chondrocytes in culture were pulse-labeled with [35S]-methionine. The CSPG core protein was identified by immunoprecipitation. The Mr of the cartilage cell-synthetized core protein was determined to be 370K, approximately 10-15K greater than that of the comparable cell-free translation product. Experimental results strongly support the view that the observed difference in Mr reflects the cotranslational addition of mannose-rich, N-asparagine-linked oligosaccharides to the cell-synthesized core protein: 1) the cell-synthesized product was labeled with [3H]-mannose and precipitated by concanavalin A-sepharose beads; 2) the incorporated [3H]-mannose could be subsequently removed by digestion with endoglycosidase H (Endo H); 3) the Mr of the cell-synthesized core protein was reduced by Endo H digestion to that of the comparable cell-free translation product; 4) the core protein synthesized by tunicamycin-treated chondrocytes (inhibited in their ability to add N-asparagine-linked mannose-rich oligosaccharides to proteins) was comparable in electrophoretic mobility to that of the core protein cell-free translation product; and 5) the core protein translated in microsome-coupled cell-free reactions had an Mr 8-10K greater than that of the core protein translated in the absence of microsomes. For the purpose of examining biosynthetic intermediates, chondrocytes were labeled continuously or pulse-chase labeled for varying times. No biosynthetic CSPG intermediates migrating between the core protein and the CSPG monomer were detected. However, a band of 355Kdal appeared to share certain characteristics with the 307Kdal core protein (including its immunoprecipitability with CSPG antibodies), and a 340Kdal band was noted. Type II procollagen and other collagenase-sensitive products of 205Kdal and 110Kdal were observed among translation and chondrocyte-synthesized products. In chondrocytes, all three products exhibited labeling or chase time-dependent increases in Mr which were accelerated by ascorbate supplements and inhibited by the addition of alpha, alpha'-dipyridyl. These results suggest that the observed time-dependent increases in Mr are a consequence of collagen hydroxylation. The 110Kdal and 205Kdal collagenous proteins may be related to the minor collagens recently described in cartilage.

Collagen synthesis in the vaginal connective tissue of patients with and without uterine prolapse

The insufficiency of connective tissue in pelvic relaxation was studied in five patients with uterine descent and in five age-related controls. Samples from vaginal fascias were first studied by histology. Fibroblast cultures started from each sample were analysed for their collagen synthesis and content of type I procollagen messenger RNAs (mRNAs). The cellularity of the fascias in histological specimens and the biosynthesis of collagen in fibroblast cultures decreased with increasing age in both groups. Fibroblasts grown from patients with uterine descent exhibited rates of collagen synthesis similar to or slightly higher than those from age-matched controls. The histological and biochemical changes observed in connective tissue of uterine descent are most likely related to the age and hormonal status of the patients. The findings suggest that uterine descent is not related to defects in the capacity of vaginal fibroblasts to synthesize or process procollagen.

Localization of types I, II, and III collagen mRNAs in developing human skeletal tissues by in situ hybridization

Paraffin sections of human skeletal tissues were studied in order to identify cells responsible for production of types I, II, and III collagens by in situ hybridization. Northern hybridization and sequence information were used to select restriction fragments of cDNA clones for the corresponding mRNAs to obtain probes with a minimum of cross-hybridization. The specificity of the probes was proven in hybridizations to sections of developing fingers: osteoblasts and chondrocytes, known to produce only one type of fibrillar collagen each (I and II, respectively) were only recognized by the corresponding cDNA probes. Smooth connective tissues exhibited variable hybridization intensities with types I and III collagen cDNA probes. The technique was used to localize the activity of type II collagen production in the different zones of cartilage during the growth of long bones. Visual inspection and grain counting revealed the highest levels of pro alpha 1(II) collagen mRNAs in chondrocytes of the lower proliferative and upper hypertrophic zones of the growth plate cartilage. This finding was confirmed by Northern blotting of RNAs isolated from epiphyseal (resting) cartilage and from growth zone cartilage. Analysis of the osseochondral junction revealed virtually no overlap between hybridization patterns obtained with probes specific for type I and type II collagen mRNAs. Only a fraction of the chondrocytes in the degenerative zone were recognized by the pro alpha 1(II) collagen cDNA probe, and none by the type I collagen cDNA probe. In the mineralizing zone virtually all cells were recognized by the type I collagen cDNA probe, but only very few scattered cells appeared to contain type II collagen mRNA. These data indicate that in situ hybridization is a valuable tool for identification of connective tissue cells which are actively producing different types of collagens at the various stages of development, differentiation, and growth.

Exclusion of the alpha 2(I) and alpha 1(III) collagen genes as the mutant loci in a Marfan syndrome family

The inheritance of restriction fragment length polymorphisms for two fibrillar collagen genes (COL1A2 and COL3A1) has been studied in a large Marfan syndrome kindred. We are able to show discordant segregation between the Marfan syndrome and each of the two collagen gene markers.

Partial characterization of a low molecular weight human collagen that undergoes alternative splicing

A cDNA library prepared from RNA isolated from a cultured human tumor cell line, HT-1080, was screened with a mouse cDNA clone coding for part of the -Gly-Xaa-Yaa- domain of the alpha 2(IV) collagen chain. Four overlapping cDNA clones were characterized that coded for a low molecular weight human collagen. The cDNA clones did not, however, code for the short-chain collagens, types IX and X. The amino acid sequences derived from the clones resembled type IV collagen in that there were short interruptions in the repeating -Gly-Xaa-Yaa- sequence. The noncollagenous, carboxyl-terminal domain was, however, much shorter and contained only 18 amino acid residues. Interestingly, one of the cDNA clones contained an additional 36 nucleotides not found in an overlapping clone. The 36 nucleotides encoded four -Gly-Xaa-Yaa- repeats without changing the reading frame. Nuclease S1 mapping demonstrated that the difference between the clones was due to existence of two different mRNAs. A synthetic 24-residue peptide corresponding to the last two -Gly-Xaa-Yaa- triplets and the entire carboxyl-terminal domain was used to generate polyclonal antibodies. Electrophoretic transfer blot analysis of HT-1080 cells and normal human skin fibroblasts identified two polypeptides, Mr 67,000 and Mr 62,000, that were sensitive to bacterial collagenase.

Differential expression of fibrillar collagen genes during callus formation

An experimental fracture healing model in the rat tibio-fibular bone was employed to study the appearance of messenger RNAs for types I, II and III collagens during endochondral fracture repair. Total RNA was extracted from normal bone and from callus tissue at various time points. The total RNAs were analyzed in Northern hybridization for their contents of procollagen mRNAs using specific cDNA clones. The results show that during the first week of fracture repair type III collagen mRNA is increased to the greatest extent, followed by type II collagen mRNA during the second week. The 28-day callus resembles bone by containing mainly type I collagen mRNAs and very little type II or III collagen mRNA.

Human collagen genes encoding basement membrane alpha 1 (IV) and alpha 2 (IV) chains map to the distal long arm of chromosome 13

At least 20 genes encode the structurally related collagen chains that comprise greater than 10 homo- or heterotrimeric types. Six members of this multigene family have been assigned to five chromosomes in the human genome. The two type I genes, alpha 1 and alpha 2, are located on chromosomes 17 and 7, respectively, and the alpha 1 (II) gene is located on chromosome 12. Our recent mapping of the alpha 1 (III) and alpha 2 (V) genes to the q24.3----q31 region of chromosome 2 provided the only evidence that the collagen genes are not entirely dispersed. To further determine their organization, we and others localized the alpha 1 (IV) gene to chromosome 13 and in our experiments sublocalized the gene to band q34 by in situ hybridization. Here we show the presence of the alpha 2 type IV locus also on the distal long arm of chromosome 13 by hybridizing a human alpha 2 (IV) cDNA clone to rodent-human hybrids and to metaphase chromosomes. To our knowledge, these studies represent the only demonstration of linkage between genes encoding both polypeptide chains of the same collagen type.

Lethal osteogenesis imperfecta resulting from a single nucleotide change in one human pro alpha 1(I) collagen allele

We have characterized a mutation in a pro alpha 1(I) procollagen gene (COL1A1) that results in lethal (type II) osteogenesis imperfecta. The mutation is a single base change that results in a cysteine-for-glycine substitution at position 988 of the triple-helical portion of half of the alpha 1(I) chains of type I collagen. The mutation thus disrupts the (Gly-Xaa-Yaa)n pattern necessary for triple-helix formation, where Xaa and Yaa are other amino acids. These experiments establish the minimal mutation in a type I collagen gene capable of producing lethal disease, and the lethality demonstrates a selective mechanism for the stringent maintenance of the collagen gene structure.

Discrimination among multiple AATAAA sequences correlates with interspecies conservation of select 3' untranslated nucleotides

The DNA sequence corresponding to the 1.3 kb 3' untranslated region of the 6.5 kb human procollagen alpha 1(IV) mRNA was determined and compared with the mouse sequence obtained from 3' cDNA and genomic clones overlapping the reported 5' half (Oberbaumer et al., 1985, Eur. J. Biochem. 147:217). Although four AAUAAA hexanucleotides are found in the human and seven in the mouse RNAs, Northern blot hybridization showed almost exclusive utilization of the most 3' sequence, in contrast to the pattern seen when using alpha 1(I), alpha 2(I), alpha 1(III) and alpha 2(V) procollagen probes. Moreover, the ninety nucleotides 5' to the poly A tail in the major alpha 1(IV) mRNAs exhibit a much greater degree of interspecies homology than those encompassing the other three shared AAUAAA recognition signals. Further examination of this highly conserved area revealed the presence of two "consensus sequences" found in the 3' noncoding region of a number of RNA polymerase II transcribed genes (Mattaj and Zeller, 1983, Embo J. 2:1883) and, unexpectedly, some similarity with the nucleotides 5' to the poly A attachment signals in other procollagen mRNAs.

The extracellular matrix is an integrated unit: ultrastructural localization of collagen types I, III, IV, V, VI, fibronectin, and laminin in human term placenta

The human term placenta is used extensively as a source of extracellular matrix components. To elucidate the tissue distribution and interrelationships of seven of these components, monospecific antibodies directed against collagen types I, III, IV, V, VI, fibronectin, and laminin were reacted with human term placenta and studied by light and electron immunohistochemistry. Type I collagen was the basic structural unit of human term placenta, present as 30-35 nm, cross-banded fibers, often in the form of large fiber bundles. Type III collagen was present as thin 10-15 nm, beaded fibers often forming a meshwork which encased type I collagen fibers. Types V and VI collagen were present as 6-10 nm filaments, often closely associated with types I and III collagen. Type VI collagen also coated collagen fibers of all diameters, enhancing their periodicity, providing a staining pattern often similar to that observed with anti-fibronectin antibodies. Fibronectin was present in both maternal and fetal plasma and throughout the stroma of the chorionic villus, as both free filaments and coating collagen fibers. Basement membranes contained laminin and type IV collagen, but no fibronectin. In summary, the non-basement membrane proteins studied often codistributed with type I collagen, between and apparently attached to fibers, suggesting that they may act as binding proteins, linking type I fibers and bundles, to themselves and to other structures.

The human type II collagen gene (COL2A1) assigned to 12q14.3

A cosmid clone containing the entire human type II alpha 1 collagen gene (COL2A1) was used as probe in the Southern analysis of DNA from a panel of human/hamster somatic cell hybrids containing different portions of human chromosome 12. Two of the hybrids exhibited a similar terminal deletion q14.3----qter, but one was positive for the gene while the other was negative. Therefore, the gene must reside in the region q14.3.

Elastin production in human skin fibroblast cultures and its decline with age

Recent studies have established that cultured human skin fibroblasts secrete the soluble precursor of elastin, tropoelastin (TE). The present studies evaluate, by an enzyme-linked immunosorbent assay, the stability of the TE phenotype and the effect of culture conditions and donor age on TE accumulation by human skin fibroblasts. Tropoelastin was maximally produced by 2 control fibroblast strains at early confluency (32-49 X 10(3) molecules/cell/h), and its serum-dependent accumulation in the medium was linear for at least 72 h. Inhibition of cross-linking had no effect on the rate of elastin production. Optimum serum concentrations for TE production differed for fibroblast cell strains derived from foreskin and trunk skin fibroblasts. Production of TE by human skin fibroblasts was stable through nearly 30 population doublings after which there was a greater than 2-fold decline in the rate of accumulation. In a cohort of donor strains, TE production appeared to decline at donor ages greater than or equal to 70 years. Under standard culture conditions, cell strains from normal donors of various ages produced TE at rates ranging from 25-69 X 10(3) molecules/cell/h. Rates of TE accumulation in medium were not significantly altered by degradation of TE, as a variety of cell strains tested exhibited minimal cell-associated elastolytic activity. Based on the demonstration of a stable elastin phenotype, skin fibroblast cultures provide a new system for studying regulation of elastin biosynthesis and evaluating potential defects in elastin metabolism associated with certain connective tissue disorders.

Isolation and purification of cyanogen bromide-derived peptides of type II collagen directly from tissue (Swarm chondrosarcoma)

A preparative procedure is described for isolating type II collagen-fragments directly from tissue. Swarm chondrosarcoma from rat, a cartilagenous tissue rich in type II collagen, was digested by cyanogen bromide in 70% formic acid. The resulting crude extract was desalted (G 25 column chromatography) and lyophylized. The yield of peptide mixture was about 1 250 mg obtained from 100 g tissue. The method of purification commonly used for type II collagen prior to cyanogen bromide-cleavage yielded 20 mg peptides from 100 g tissue. Separation of the cyanogen bromide-derived fragments was performed by gel filtration. The column was run at 43 degrees C (denaturing-temperature of collagens) to avoid fibril formation, and a volatile buffer was used (ammonium formate buffer, pH 7.5) so that the effluent fractions could be easily lyophylized. Two-dimensional gel electrophoresis of the main peaks of the column profile demonstrated that this purification step resulted in a good separation of the fragment mixture, although additional steps may be necessary for complete separation of the peptides. The most striking advantages of the method for direct digestion of tissue outlined here are the increase in yield (about 60-fold) and the reduction of purification steps (avoiding type II collagen purification).