Complete nucleotide sequence of the region encompassing the first twenty-five exons of the human pro alpha 1(I) collagen gene (COL1A1)

Cloning, tissue distribution and mRNA expression of type I collagen alpha 1 gene from Chu's croaker (Nibea coibor)

The demand for collagen has been increasing over years due to its wide application in food, cosmetics and biomedicine industries. The synthesis of collagen protein in fish depends on instructions provided by collagen, type I, alpha 1 (COL1A1) gene. However, cloning, tissue distribution and mRNA expression of COL1A1 gene in a gel-producing Chu's croaker (Nibea coibor) is currently unknown. This study cloned the cDNA of COL1A1 gene (GenBank accession number: MK641512) from six N. coibor fish. The distribution and mRNA expression pattern of COL1A1 was analyzed in eight tissues of N. coibor. The COL1A1 cDNA had a full length of 6130 bp and contained a 4344 bp open reading frame (ORF) encoding a polypeptide of 1448 amino acids. The homology of N. coibor COL1A1 amino acid had 98% similarity with Larimichthys crocea, indicating conservatism with other members in same family (Sciaenidae). The deduced polypeptide contained the same signal peptides, C-propeptide and N-propeptide domains, and triple helix domains, which are the characteristics of type I collagen in vertebrates. The mRNA of COL1A1 gene was expressed significantly higher in the spine of N. coibor than in all other tissues (P < 0.05), followed by swim bladder, skin and scales. The swim bladder had higher collagen and hydroxyproline contents than other tissues, followed by spine >, scales > and > skin (P < 0.05). Our study successfully cloned the COL1A1 gene from N. coibor for the first time. The COL1A1 gene contained all the features of collagen pro-α1(I) chain proteins, and shared high homology with other marine teleost. COL1A1 gene in N. coibor is highly expressed in spine and swim bladder, consistent with collagen distribution. Our study contributes to better understanding on collagen biosynthesis in N. coibor tissues for various industrial uses.

An ENU-induced splice site mutation of mouse Col1a1 causing recessive osteogenesis imperfecta and revealing a novel splicing rescue

GU-AG consensus sequences are used for intron recognition in the majority of cases of pre-mRNA splicing in eukaryotes. Mutations at splice junctions often cause exon skipping, short deletions, or insertions in the mature mRNA, underlying one common molecular mechanism of genetic diseases. Using N-ethyl-N-nitrosourea, a novel recessive mutation named seal was produced, associated with fragile bones and susceptibility to fractures (spine and limbs). A single nucleotide transversion (T → A) at the second position of intron 36 of the Col1a1 gene, encoding the type I collagen, α1 chain, was responsible for the phenotype. Col1a1 ^seal mRNA expression occurred at greatly reduced levels compared to the wild-type transcript, resulting in reduced and aberrant collagen fibers in tibiae of seal homozygous mice. Unexpectedly, splicing of Col1a1 ^seal mRNA followed the normal pattern despite the presence of the donor splice site mutation, likely due to the action of a putative intronic splicing enhancer present in intron 25, which appeared to function redundantly with the splice donor site of intron 36. Seal mice represent a model of human osteogenesis imperfecta, and reveal a previously unknown mechanism for splicing "rescue."

Involvement of fibrocytes in asthma and clinical implications

Bloodborne fibrocytes are bone marrow-derived cells that participate in immune responses and exhibit pro-inflammatory and matrix remodelling properties. In patients with asthma receiving an adequate treatment, the blood fibrocyte count is very low and comparable to that obtained in healthy individuals. In these patients, a transient increase in fibrocyte numbers in the peripheral blood and in the airways occurs in concomitance with increased bronchial inflammation and reflects disease worsening and the need for more intensive treatment. Persistently elevated numbers of fibrocytes in the peripheral blood and in the bronchial mucosa are observed in chronically undertreated or corticosteroid-resistant asthma and are associated with persistent airway inflammation and ongoing remodelling of the bronchial wall. The asthmatic bronchial epithelium is the main source of fibrocyte chemoattractants in asthma and contributes with T helper type 2 lymphocytes and eosinophils to promote the proliferation and pro-remodelling function of recruited fibrocytes. The presence of elevated numbers of fibrocytes in the bronchial mucosa of allergic patients with undertreated or treatment-resistant asthma may also increase the risk of acute exacerbations because these cells can amplify T helper type 2 lymphocyte-driven inflammation on every exposure to the clinically relevant allergen and can promote further inflammation on rhinovirus infections by allowing viral replication and releasing additional pro-inflammatory factors. Improved methods for the isolation and functional analysis of pure populations of viable circulating fibrocytes have allowed a better understanding of the effector role of these cells. A reliable and clinically applicable assay has been developed to measure blood fibrocyte counts as outcome measure in future clinical trials. New therapeutic agents are needed to block both persistent inflammation and fibrocytosis in corticosteroid-resistant asthma.

Mutation of the 5'-untranslated region stem-loop structure inhibits α1(I) collagen expression in vivo

Type I collagen is a heterotrimeric extracellular matrix protein consisting of two α1(I) chains and one α2(I) chain. During liver fibrosis, activated hepatic stellate cells (HSCs) are the major source of the type I collagen that accumulates in the damaged tissue. Expression of α1(I) and α2(I) collagen mRNA is increased 60-fold compared with quiescent stellate cells and is due predominantly to post-transcriptional message regulation. Specifically, a stem-loop structure in the 5'-untranslated region of α1(I) collagen mRNA may regulate mRNA expression in activated HSCs through its interaction with stem-loop binding proteins. The stem-loop may also be necessary for efficient production and folding of the type I collagen heterotrimer. To assess the role of the stem-loop in type I collagen expression in vivo, we generated a knock-in mouse harboring a mutation that abolished the stem-loop structure. Heterozygous and homozygous knock-in mice exhibited a normal phenotype. However, steady-state levels of α1(I) collagen mRNA decreased significantly in homozygous mutant MEFs as well as HSCs; intracellular and secreted type I collagen protein levels also decreased. Homozygous mutant mice developed less liver fibrosis. These results confirm an important role of the 5' stem-loop in regulating type I collagen mRNA and protein expression and provide a mouse model for further study of collagen-associated diseases.

Collagen 1Alpha1 and transforming growth factor-beta polymorphisms in women with cervical insufficiency

OBJECTIVE

To estimate whether polymorphisms in the collagen 1Alpha1 gene (COL1Alpha1) and the transforming growth factor-beta gene (TGF-beta;1) are more common in women with cervical insufficiency than in those without the condition.

METHODS

Medical, obstetric, and family histories and blood were obtained from women with (n=121) and those without (n=165) cervical insufficiency. DNA was extracted and purified by using commercial DNA isolation kits. Samples were analyzed for variants in two genes, the COL1A1 intron 1SP1 and TGF-beta Arg-25-Pro polymorphism, by using an allele-specific polymerase chain reaction assay.

RESULTS

Thirty-four of 125 (27.2%) women with cervical insufficiency had at least one first-degree female relative affected. The frequency of the homozygous TT genotype in the COL1A1 gene was increased in women with a history of cervical insufficiency compared with controls (10.8% compared with 3.1%, P=.04). The TGF-beta polymorphisms (ArgPro and ProPro) also were increased in cases (38.3% compared with 14.6%, P<.001).

CONCLUSION

Over one fourth of women with cervical insufficiency have a family history of cervical insufficiency, and the COL1A1 intron 1SP1 and TGF-beta Arg-25-Pro polymorphisms are associated with the condition. These observations suggest that, in part, cervical insufficiency is mediated by genetic factors.

LEVEL OF EVIDENCE

II.

Alveolar bone osteoblast differentiation and Runx2/Cbfa1 expression

Alveolar bone cells have a unique origin and functionality, but may resemble skeletal osteoblasts. Osteoblast differentiation and gene expression are regulated by the Runx2/Cbfa1 transcription factor. However, most studies on Runx2/Cbfa1 expression have been on rodent cells and the few studies on human osteoblasts have had differing results. The purpose of this study was to characterize Runx2/Cbfa1 expression in primary cell cultures derived from human alveolar bone. An alveolar bone chip was incubated in alpha-minimum essential medium (alpha-MEM) supplemented with fetal calf serum (10% FCS). Explant cultures were harvested after 3-4 weeks of outgrowth and grown in alpha-MEM with FCS. This media was supplemented with ascorbate, beta-glycerophosphate and dexamethasone to promote osteoblast differentiation over 14 days. RT-PCR analysis and Western blots showed a rapid increase in Runx2/Cbfa1 mRNA (2.1-fold) and protein (2.3-fold) levels in 3 days, followed by a slight decline. There was also a rapid increase in bone sialoprotein expression (2.9-fold) in 3 days, followed by a further increase (3.6-fold) at 14 days. There was a slower increase in alkaline phosphatase expression (1.6-fold) and activity (3.1-fold) over 7 days, followed by a gradual decline. In contrast, collagen mRNA levels showed little change over 14 days. These findings attest to the osteogenic potential of primary cell cultures derived from human alveolar bone. Osteoblastic differentiation in human alveolar bone involves an increase in Runx2/Cbfa1 expression that may be an important component of the differentiation process.

cDNA cloning and characterization of Type I procollagen α1 chain in the skate Raja kenojei

A full-length cDNA of the Type I procollagen alpha1 [pro-alpha1(I)] chain (4388 bp), coding for 1463 amino acid residues in the total length, was determined by RACE PCR using a cDNA library constructed from 4-week embryo of the skate Raja kenojei. The helical region of the skate pro-alpha1(I) chain consisted of 1014 amino acid residues - the same as other fibrillar collagen alpha chains from higher vertebrates. Comparison on denaturation temperatures of Type I collagens from the skate, rainbow trout (Oncorhynchus mykiss) and rat (Rattus norvegicus) revealed that the number of Gly-Pro-Pro and Gly-Gly in the alpha1(I) chains could be directly related to the thermal stability of the helix. The expression property of the skate pro-alpha1(I) chain mRNA and phylogenetic analysis with other vertebrate pro-alpha1(I) chains suggested that skate pro-alpha1(I) chain could be a precursor form of the skate Type I collagen alpha1 chain. The present study is the first evidence for the primary structure of full-length pro-alpha1(I) chain in an elasmobranch.

Integrin Expression and Osteopontin Regulation in Human Fetal Osteoblastic Cells Mediated by Substratum Surface Characteristics

Integrin-mediated adhesion of anchorage-dependent cells to scaffolds is a critical component of tissue engineering. We investigated integrin expression by the human fetal osteoblastic cell line, hFOB 1.19 (hFOB), as a function of substratum surface wettability. The influence of surface wettability on bone cell phenotype was also examined. Plasma-treated quartz (PTQ) and glass (PTG) (hydrophilic, contact angles of 0 degrees), octadecyltrichlorosilane-treated quartz (STQ) and glass (STG) (hydrophobic, contact angles above about 100 degrees), and tissue culture polystyrene were used for cell culture. hFOB cells cultured on hydrophilic substrata displayed well-developed actin stress fibers relative to cells on hydrophobic substrata. Western blot analysis revealed that hFOB cells cultured on hydrophobic substrata (STQ or STG) express lower levels of alphav and beta3 integrin subunits than do cells on hydrophilic substrata (PTQ or PTG). This effect was more pronounced in cells on STQ than on STG. These variations in integrin expression were lessened by extended culture time. Double- labeled integrin/actin immunofluorescence confirmed Western blot results, that is, cells cultured on PTQ displayed distinct, large plaques of alphav and beta3 subunits and integrin alphavbeta3, as well as their colocalization with actin stress fiber ends, whereas cells on STQ did not display integrin plaques after 24 h and displayed only minimal plaque formation after 3 days. Vinculin, a focal adhesion protein that mediates binding between the integrin and actin cytoskeleton, appeared in Western blots to mimic the variations of alphav and beta3 expression with respect to surface wettability. Interestingly, real-time RT-PCR analysis showed that hFOB cultured on hydrophobic substrata, which have downregulated alphav and beta3 integrin subunits, displayed greater steady state mRNA levels of osteopontin, an extracellular matrix (ECM) protein containing the Arg-Gly-Asp (RGD) integrin recognition sequence, than did cells cultured on hydrophilic substrata. Our results imply that substratum surface wettability regulates integrin-mediated bone cell adhesion and further influences the expression of bone cell-ECM complexes.

Procollagen with skipping of alpha 1(I) exon 41 has lower binding affinity for alpha 1(I) C-telopeptide, impaired in vitro fibrillogenesis, and altered fibril morphology

Previous in vitro data on type I collagen self-assembly into fibrils suggested that the amino acid 776-796 region of the alpha1(I) chain is crucial for fibril formation because it serves as the recognition site for the telopeptide of a docking collagen monomer. We used a natural collagen mutation with a deletion of amino acids 766-801 to confirm the importance of this region for collagen fibril formation. The proband has type III osteogenesis imperfecta and is heterozygous for a COL1A1 IVS 41 A(+4) --> C substitution. The intronic mutation causes splicing of exon 41, confirmed by sequencing of normal and shorter reverse transcriptase-PCR products. Reverse transcriptase-PCR using RNA from proband dermal fibroblasts and clonal cell lines showed the mutant cDNA was about 15% of total alpha1(I) cDNA. The mutant transcript is translated; structurally abnormal alpha chains are demonstrated in the cell layer of proband fibroblasts by SDS-urea-PAGE. The proportion of mutant chains in the secreted procollagen was determined to be 10% by resistance to digestion with MMP-1, since chains lacking exon 41 are missing the vertebral collagenase cleavage site. Secreted proband collagen was used for analysis of kinetics of binding of alpha1(I) C-telopeptide using an optical biosensor. Telopeptide had slower association and faster dissociation from proband than from normal collagen. Purified proband pC-collagen was used to study fibril formation. The presence of the mutant molecules decreases the rate of fibril formation. The fibrils formed in the presence of 10-15% mutant molecules have strikingly increased length compared with normal collagen, but are well organized, as demonstrated by D-periodicity. These results suggest that some collagen molecules containing the mutant chain are incorporated into fibrils and that the absence of the telopeptide binding region from even a small portion of the monomers interferes with fibril growth. Both abnormal fibrils and slower remodeling may contribute to the severe phenotype.in

Type IIA procollagen in development of the human intervertebral disc: regulated expression of the NH(2)-propeptide by enzymic processing reveals a unique developmental pathway

Type II collagen can be synthesized in two forms generated by alternative splicing of the precursor mRNA. Type IIA procollagen, which contains a cysteine-rich domain in the NH(2)-propeptide (exon 2), is produced by precartilage and noncartilage epithelial and mesenchymal cells, and type IIB procollagen, without the cysteine-rich domain, is characteristic of chondrocytes. Mice lacking type II collagen fail to develop intervertebral discs. We have previously shown that the human intervertebral disc and notochord synthesize primarily the type IIA form of procollagen. Therefore, we investigated the distribution of type IIA procollagen during early disc development in humans. By processes of radioactive in situ hybridization and fluorescence immunohistochemistry, we localized mRNA and protein of type IIA procollagen, type I collagen, and type III collagen in fetal intervertebral disc specimens ranging from day 42 (embryonic stage 17) to day 101 (week 14.5) of gestation. Antibodies to the three distinct domains of type IIA procollagen: the NH(2)-propeptide, the fibrillar domain, and the COOH-propeptide were used. The earliest stage of developing intervertebral disc (42 days, stage 17) was characterized by diffuse synthesis of types I and III collagens in the dense zone (intervertebral area) and synthesis of type IIA procollagen by the chondrocyte progenitor cells surrounding the disc. The notochord cells synthesized and deposited into the notochordal sheath all three fibrillar collagens. By 54 days (stage 22), the developing disc was clearly divided into three regions: 1.) the outer annulus, characterized by synthesis and deposition of types I and III collagens; 2.) the inner annulus, characterized by synthesis and deposition of type IIA collagen containing the NH(2)-propeptide but devoid of the COOH-propeptide (pN-procollagen); and 3.) the notochord, the cells of which synthesized and deposited of all three fibrillar collagens. In later stages of fetal development (72-101 days), a change in type IIA procollagen processing was observed in the cells of the inner annulus: even though these cells continued to synthesize type IIA procollagen, they deposited into the extracellular matrix (ECM) only the processed fibrillar domain, with the NH(2)-propeptide removed. This finding indicates that there is a developmentally regulated change in the processing of type IIA procollagen NH(2)-propeptide in the cells of the inner annulus. This mechanism is in contrast to previously shown developmental regulation of the cysteine-rich domain of the NH(2)-propeptide by alternative splicing of the precursor mRNA. Although the cells of the inner annulus have been identified as chondrocytes, based on their shape and synthesis of characteristic ECM components, they appear to represent a distinct developmental pathway characterized by their synthesis and differential processing of type IIA procollagen. This developmental pattern may prove important for disc regeneration.

Two new recurrent nucleotide mutations in the COL1A1 gene in four patients with osteogenesis imperfecta: about one-fifth are recurrent

Previous observations on mutations causing osteogenesis imperfecta (OI) suggested that unrelated patients had private mutations. Here preliminary studies on two patients with type I OI indicated that some mutations in the COL1A1 gene for type I procollagen cannot be detected by analyses of cDNAs. Therefore, we developed a protocol whereby 43 exon and exon flanking sequences of the COL1A1 gene can be amplified by PCR and scanned for mutations by denaturing gradient gel electrophoresis. Two new recurrent nucleotide mutations in the gene were found in four apparently unrelated patients with OI. Analysis of previous publications indicated that up to one-fifth of the mutations causing OI are recurrent in the sense that they were identical in apparently unrelated probands. About 80% of these identical mutations were in CpG dinucleotide sequences.

Production of recombinant human type I procollagen homotrimer in the mammary gland of transgenic mice

The large scale production of recombinant collagen for use in biomaterials requires an efficient expression system capable of processing a large (> 400 Kd) multisubunit protein requiring post-translational modifications. To investigate whether the mammary gland of transgenic animals fulfills these requirements, transgenic mice were generated containing the alpha S1-casein mammary gland-specific promoter operatively linked to 37 Kb of the human alpha 1(I) procollagen structural gene and 3' flanking region. The frequency of transgenic lines established was 12%. High levels of soluble triple helical homotrimeric [(alpha 1)3] type I procollagen were detected (up to 8 mg/ml) exclusively in the milk of six out of 9 lines of lactating transgenic mice. The transgene-derived human procollagen chains underwent efficient assembly into a triple helical structure. Although proline or lysine hydroxylation has never been described for any milk protein, procollagen was detected with these post-translational modifications. The procollagen was stable in milk; minimal degradation was observed. These results show that the mammary gland is capable of expressing a large procollagen gene construct, efficiently assembling the individual polypeptide chains into a stable triple helix, and secreting the intact molecule into the milk.

Nonsense mutations in the COL1A1 gene preferentially reduce nuclear levels of mRNA but not hnRNA in osteogenesis imperfecta type I cell strains

Osteogenesis imperfecta (OI) is a heterogeneous disorder of type I collagen resulting in varying degrees of severity. The mildest form of OI (Type I) is associated with bone fragility, normal or near normal stature and blue sclerae. All forms of OI are the result of mutations in COL1A1 or COL1A2, the genes that encode the proalpha1(I) and proalpha2(I) chains of type I collagen, respectively. Mutations identified in patients with OI type I lead to premature termination codons and allele-specific reductions of nuclear mRNA (termed nonsense-mediated mRNA decay or NMD), resulting in a COL1A1 null allele. In mammals, this process primarily effects RNA that co-purifies with the nuclear fraction of the cell. Using a semi-quantitative RT-PCR assay, we compare the relative amounts of normal and mutant transcripts in unprocessed hnRNA and mature mRNA isolated from the nuclear fraction of cells from 11 OI type I individuals with previously identified mutations distributed throughout the COL1A1 gene. While we detect about equal amounts of normal and mutant hnRNA from each cell strain, there is preferential reduction in the relative amount of mutant mRNA when compared to normal; only the cell strain with a mutation in the last exon escapes the major effects of NMD. Our data indicate that NMD targets mRNA rather than hnRNA for degradation, and that this occurs either during or after splicing but prior to cytoplasmic translation.

Complete sequence of the 23-kilobase human COL9A3 gene. Detection of Gly-X-Y triplet deletions that represent neutral variants

We report the complete sequence of the human COL9A3 gene that encodes the alpha3 chain of heterotrimeric type IX collagen, a member of the fibril-associated collagens with interrupted triple helices family of collagenous proteins. Nucleotide sequencing defined over 23,000 base pairs (bp) of the gene and about 3000 bp of the 5'-flanking sequences. The gene contains 32 exons. The domain and exon organization of the gene is almost identical to a related gene, the human COL9A2 gene. However, exon 2 of the COL9A3 gene codes for one -Gly-X-Y- triplet less than exon 2 of the COL9A2 gene. The difference is compensated by an insertion of 9 bp coding for an additional triplet in exon 4 of the COL9A3 gene. As a result, the number of -Gly-X-Y- repeats in the third collagenous domain remains the same in both genes and ensures the formation of an in-register triple helix. In the course of screening this gene for mutations, heterozygosity for separate 9-bp deletions within the COL1 domain were identified in two kindreds. In both instances, the deletions did not co-segregate with any disease phenotype, suggesting that they were neutral variants. In contrast, similar deletions in triple helical domain of type I collagen are lethal. To study whether alpha3(IX) chains with the deletion will participate in the formation of correctly folded heterotrimeric type IX collagen, we expressed mutant alpha3 chains together with normal alpha1 and alpha2 chains in insect cells. We show here that despite the deletion, mutant alpha3 chains were secreted as heterotrimeric, triple helical molecules consisting of three alpha chains in a 1:1:1 ratio. The results suggest that the next noncollagenous domain (NC2) is capable of correcting the alignment of the alpha chains, and this ensures the formation of an in-register triple helix.

Redefinition of exon 7 in the COL1A1 gene of type I collagen by an intron 8 splice-donor-site mutation in a form of osteogenesis imperfecta: influence of intron splice order on outcome of splice-site mutation

Most splice-site mutations lead to a limited array of products, including exon skipping, use of cryptic splice-acceptor or -donor sites, and intron inclusion. At the intron 8 splice-donor site of the COL1A1 gene, we identified a G+1-->A transition that resulted in the production of several splice products from the mutant allele. These included one in which the upstream exon 7 was extended by 96 nt, others in which either intron 8 or introns 7 and 8 were retained, one in which exon 8 was skipped, and one that used a cryptic donor site in exon 8. To determine the mechanism by which exon-7 redefinition might occur, we examined the order of intron removal in the region of the mutation by using intron/exon primer pairs to amplify regions of the precursor nuclear mRNA between exon 5 and exon 10. Removal of introns 5, 6, and 9 was rapid. Removal of intron 8 usually preceded removal of intron 7 in the normal gene, although, in a small proportion of copies, the order was reversed. The proportion of abnormal products suggested that exon 7 redefinition, intron 7 plus intron 8 inclusion, and exon 8 skipping all represented products of the impaired rapid pathway, whereas the intron-8 inclusion product resulted from use of the slow intron 7-first pathway. The very low-abundance cryptic exon 8 donor site product could have arisen from either pathway. These results suggest that there is commitment of the pre-mRNA to the two pathways, independent of the presence of the mutation, and that the order and rate of intron removal are important determinants of the outcome of splice-site mutations and may explain some unusual alterations.

Regulatory role of the conserved stem-loop structure at the 5' end of collagen alpha1(I) mRNA

Three fibrillar collagen mRNAs, alpha1(I), alpha2(I), and alpha1(III), are coordinately upregulated in the activated hepatic stellate cell (hsc) in liver fibrosis. These three mRNAs contain sequences surrounding the start codon that can be folded into a stem-loop structure. We investigated the role of this stem-loop structure in expression of collagen alpha1(I) reporter mRNAs in hsc's and fibroblasts. The stem-loop dramatically decreases accumulation of mRNAs in quiescent hsc's and to a lesser extent in activated hsc's and fibroblasts. The stem-loop decreases mRNA stability in fibroblasts. In activated hsc's and fibroblasts, a protein complex binds to the stem-loop, and this binding requires the presence of a 7mG cap on the RNA. Placing the 3' untranslated region (UTR) of collagen alpha1(I) mRNA in a reporter mRNA containing this stem-loop further increases the steady-state level in activated hsc's. This 3' UTR binds alphaCP, a protein implicated in increasing stability of collagen alpha1(I) mRNA in activated hsc's (B. Stefanovic, C. Hellerbrand, M. Holcik, M. Briendl, S. A. Liebhaber, and D. A. Brenner, Mol. Cell. Biol. 17:5201-5209, 1997). A set of protein complexes assembles on the 7mG capped stem-loop RNA, and a 120-kDa protein is specifically cross-linked to this structure. Thus, collagen alpha1(I) mRNA is regulated by a complex interaction between the 5' stem-loop and the 3' UTR, which may optimize collagen production in activated hsc's.

Conformation sensitive gel electrophoresis for simple and accurate detection of mutations: comparison with denaturing gradient gel electrophoresis and nucleotide sequencing

Previously, an assay called conformation sensitive gel electrophoresis (CSGE) was developed for scanning PCR products for the presence of single-base and larger base mismatches in DNA. The assay was based on the assumption that mildly denaturing solvents in an appropriate buffer can accentuate the conformational changes produced by single-base mismatches in double-stranded DNA and thereby increase the differential migration in electrophoretic gels of heteroduplexes and homoduplexes. Here the sensitivity of assays by CSGE was improved by limiting the maximal size of the PCR products to 450 bp and making several changes in the conditions for PAGE. With the improved conditions, CSGE detected all 76 previously identified single-base changes in a large series of PCR products from collagen genes that contain multiple exons with highly repetitive and GC-rich sequences. In a survey of 736 alleles of collagen genes, CSGE detected 223 unique single-base mismatches that were confirmed by nucleotide sequencing. CSGE has the advantage over other methods for scanning PCR products in that it is simple, requires no special preparation of PCR products, has a large capacity, and does not use radioactivity.

Analysis of the COL1A1 and COL1A2 genes by PCR amplification and scanning by conformation-sensitive gel electrophoresis identifies only COL1A1 mutations in 15 patients with osteogenesis imperfecta type I: identification of common sequences of null-allele mutations

Although >90% of patients with osteogenesis imperfecta (OI) have been estimated to have mutations in the COL1A1 and COL1A2 genes for type I procollagen, mutations have been difficult to detect in all patients with the mildest forms of the disease (i.e., type I). In this study, we first searched for mutations in type I procollagen by analyses of protein and mRNA in fibroblasts from 10 patients with mild OI; no evidence of a mutation was found in 2 of the patients by the protein analyses, and no evidence of a mutation was found in 5 of the patients by the RNA analyses. We then searched for mutations in the original 10 patients and in 5 additional patients with mild OI, by analysis of genomic DNA. To assay the genomic DNA, we established a consensus sequence for the first 12 kb of the COL1A1 gene and for 30 kb of new sequences of the 38-kb COL1A2 gene. The sequences were then used to develop primers for PCR for the 103 exons and exon boundaries of the two genes. The PCR products were first scanned for heteroduplexes by conformation-sensitive gel electrophoresis, and then products containing heteroduplexes were sequenced. The results detected disease-causing mutations in 13 of the 15 patients and detected two additional probable disease-causing mutations in the remaining 2 patients. Analysis of the data developed in this study and elsewhere revealed common sequences for mutations causing null alleles.

Differential myocardial abundance of collagen type I and type III mRNA in dilated cardiomyopathy: effects of myocardial inflammation

OBJECTIVE

The collagen subtypes I (Col I) and III (Col III) are essential components of the cardiac extracellular matrix (ECM) maintaining the functional integrity of the heart. Histological, immunohistological, and biochemical studies, however, demonstrate characteristical changes of the ECM in dilated cardiomyopathy, myocarditis, ischemic cardiomyopathy, and hypertensive heart disease.

METHODS

In order to investigate possible effects of inflammatory processes on mRNA abundance of Col I and Col III, we examined 24 patients with the presumptive clinical diagnosis of dilated cardiomyopathy (EF = 30 +/- 11%). 12 Patients were classified as idiopathic dilated cardiomyopathy without any evidence of myocardial inflammation; the remaining 12 patients were classified as inflammatory cardiomyopathy due to the immunohistologically documented inflammatory myocardial process.

RESULTS

Quantification of reverse transcription polymerase chain reaction (RT-PCR) products revealed significant differences as to the mRNA abundance ratio Col III/Col I between subgroups of patients with inflammatory cardiomyopathy (1.16 +/- 0.18) and idiopathic dilated cardiomyopathy (2.77 +/- 0.65) regardless of left ventricular dysfunction (p < or = 0.05).

CONCLUSION

It is not yet known, whether different Col III/Col I ratios differentially influence diastolic compliance. Our data suggest that inflammatory mechanisms seen in inflammatory cardiomyopathy influence the mRNA abundance of collagen subtypes I and III.

Ehlers-Danlos syndrome type VIIA and VIIB result from splice-junction mutations or genomic deletions that involve exon 6 in the COL1A1 and COL1A2 genes of type I collagen

Ehlers-Danlos syndrome (EDS) type VII results from defects in the conversion of type I procollagen to collagen as a consequence of mutations in the substrate that alter the protease cleavage site (EDS type VIIA and VIIB) or in the protease itself (EDS type VIIC). We identified seven additional families in which EDS type VII is either dominantly inherited (one family with EDS type VIIB) or due to new dominant mutations (one family with EDS type VIIA and five families with EDS type VIIB). In six families, the mutations alter the consensus splice junctions, and, in the seventh family, the exon is deleted entirely. The COL1A1 mutation produced the most severe phenotypic effects, whereas those in the COL1A2 gene, regardless of the location or effect, produced congenital hip dislocation and other joint instability that was sometimes very marked. Fractures are seen in some people with EDS type VII, consistent with alterations in mineral deposition on collagen fibrils in bony tissues. These new findings expand the array of mutations known to cause EDS type VII and provide insight into genotype/phenotype relationships in these genes.

Collagen II containing a Cys substitution for arg-alpha1-519. Homotrimeric monomers containing the mutation do not assemble into fibrils but alter the self-assembly of the normal protein

A recombinant system was used to prepare human type II procollagen containing the substitution of Cys for Arg at alpha1-519 found in three unrelated families with early onset generalized osteoarthritis together with features of a mild chondrodysplasia probably best classified as spondyloepiphyseal dysplasia. In contrast to mutated procollagens containing Cys substitutions for obligatory Gly residues, the Cys substitution at alpha1-519 did not generate any intramolecular disulfide bonds. The results were consistent with computer modeling experiments that demonstrated that the alpha carbon distances were shorter with Cys substitutions for obligatory Gly residues than with Cys substitutions in the Y position residues in repeating -Gly-X-Y- sequences of the collagen triple helix. The mutated collagen did not assemble into fibrils under conditions in which the normal monomers polymerized. However, the presence of the mutated monomer in mixtures with normal collagen II increased the lag time for fibril assembly and altered the morphology of the fibrils formed.

Gene expression of type II collagens in chondro-osteophytes in experimental osteoarthritis

The formation of chondro-osteophytes in osteoarthritic joints is a unique example of adult neochondrogenesis that bears some similarities to growth plate elongation and fracture callus formation. This study uses in situ hybridization histochemistry to define the molecular phenotype of cells in active chondro-osteophytes. Chondro-osteophytes are composed of fibrocytes and osteoblasts that express type I procollagen mRNA, mesenchymal prechondrochytes that express type IIA procollagen mRNA, and maturing chondrocytes that express type IIB procollagen mRNA. Based on the spatial pattern of gene expression and cytomorphology, the neochondrogenesis associated with chondro-osteophyte formation closely resembles that of healing fracture callus.

The human type I collagen mutation database

Type I collagen is the most abundant and ubiquitously distributed of the collagen family of proteins. It is a heterotrimer comprising two alpha1(I) chains and one alpha2(I) chain which are encoded by the unlinked loci COL1A1 and COL1A2 respectively. Mutations at these loci result primarily in the connective tissue disorders osteogenesis imperfecta and Ehlers-Danlos syndrome types VIIA and VIIB. Two instances of osteoporosis and a single instance of Marfan syndrome are also the result of mutations at these loci. The mutation data are accessible on the world wide web at http://www.le.ac.uk/depts/ge/collagen/collagen.html

Molecular site specificity of pyridinoline and pyrrole cross-links in type I collagen of human bone

Compared with soft tissue collagens, bone type I collagen displays a distinctive pattern of covalent cross-linking, with evidence of preferred sites of molecular interaction and a prominence of both immature, divalent cross-links and mature, trivalent cross-links in the adult tissue. In this study the site-specificity of the mature cross-links in human bone collagen was examined. Peptides containing fluorescent pyridinoline cross-links and Ehrlich's-reactive pyrrole cross-links were isolated from a bacterial collagenase digest of demineralized bone matrix. The digest was fractionated by molecular sieve chromatography, monitoring for peptide absorbance, pyridinoline fluorescence, pyrroles by Ehrlich's reagent, and immunoassay for cross-linked N-telopeptides. Individual cross-linked peptides were resolved by ion-exchange and reverse-phase HPLC. Structures were established by NH2-terminal microsequencing, cross-link analysis, electrospray mass spectrometry, and immunoassay. Two, about equally occupied, sites of pyridinoline cross-linking were identified, N-telopeptide to helix and C-telopeptide to helix. Pyrroles were alternative cross-linking products at the same sites, but concentrated (85%) at the N-telopeptide end. Only one combination of chains was cross-linked by pyridinolines at the C-telopeptide to helix site, [alpha1(I)C]2alpha1(I)helix. Several peptide combinations arose from the N-telopeptide to helix site, but the main source of pyridinolines was from the locus, alpha1(I)Nalpha2(I)Nalpha1(I)helix. Pyridinolines linking two alpha1(N) telopeptides were a minor component. Pyrroles were concentrated at the locus, alpha1(I)Nalpha2(I)Nalpha2(I)helix. The cross-link ratio of hydroxylysylpyridinoline to lysylpyridinoline differed between N-telopeptide and C-telopeptide sites, and between the individual interchain combinations. Cross-linked N-telopeptides accounted for two-thirds of the total lysylpyridinoline in bone. N-telopeptide pyridinoline fluorescence was quenched on chromatography, so that reliance on peptide fluorescence alone can underestimate the level of N-telopeptide pyridinoline cross-linking.

Developmental regulation of collagen differential expression in the rabbit bladder

PURPOSE

It has been suggested that the amount and relative ratios of different types of collagen influence bladder compliance. To understand the mechanisms regulating collagen synthesis and degradation in the bladder we investigated the gene expression of collagen types I and III in the rabbit bladder during normal development.

MATERIALS AND METHODS

New Zealand white rabbits ages fetus to adult were used for this study. The mid portion of the bladder wall was harvested. Northern blot hybridization was performed to analyze quantitatively collagen types I and III messenger (m) ribonucleic acid (RNA), and in situ hybridization was done to localize the messages. Corresponding protein distributions were obtained by immunohistochemical staining.

RESULTS

Types I and III collagen are developmentally regulated at the level of gene expression. The temporal and spatial distribution of the mRNA transcripts of alpha 1(I) and alpha 1(III) correlates with extracellular protein deposition. Differential distribution of the mRNA transcripts is also developmentally regulated.

CONCLUSIONS

This study characterizes the relationship between collagen gene expression and normal rabbit bladder development. The expression of alpha 1(I) and alpha 1(III) alters as the bladder grows. High levels and nonconcordant up and down regulation of different types of collagen mRNA during early development demonstrate the complexity of the extracellular matrix in a young bladder. This observation may be important in our understanding of the injury response in a developing versus mature bladder.

Chondrogenesis in the regenerating antler tip in red deer: expression of collagen types I, IIA, IIB, and X demonstrated by in situ nucleic acid hybridization and immunocytochemistry

The annual regrowth of antlers in male deer is a unique example of complete bone regeneration occurring in an adult animal. Growth is initiated at the distal antler tip, which is similar to the epiphyseal growth plate in some respects. However, there is some debate as to whether this process represents "true" endochondral ossification. As part of the characterization of the developmental process in pre-osseus antler tissue, we have studied, by in situ hybridization, the spatial expression of mRNAs for types I, II, and X collagen. Viewed in a coronal plane, type I procollagen mRNA was observed in skin, the fibrous perichondrium, and the densely cellular area immediately adjacent to the perichondrium. Below this area, as cells began to assume a columnar arrangement and coincident with the appearance of a vasculature and synthesis of a cartilaginous matrix, transcripts for types I, IIA, IIB procollagen and X collagen were detected. Further down in the cartilage zone, the pattern of type I procollagen mRNA expression was altered. Here, the signal was detected only in a morphologically distinct subpopulation of small, flattened cells within the intercellular matrix at the periphery of the columns of chondrocytes. The alternative splice form of type II procollagen mRNA (IIA), characteristic of chondroprogenitor cells (Sandell et al. [1991] J. Cell Biol. 114:1307-1319), was expressed by a subset of cells in the upper region of the columns, indicating that this zone contains a population of prechondrocytic cells. Positive hybridization to type IIA was most abundant in these cells. In contrast, transcripts for the other procollagen splice form (IIB) and type X collagen were expressed by chondrocytes throughout the whole of the cartilage region studied. The translation and export of type II collagen and type X collagen were confirmed by detecting specific immunoreactivity for each. The spatial distribution of immunoreactivity for collagen types II and X was consistent with that of corresponding mRNAs. These data demonstrate for the first time the distinct pattern of expression of genes for major cartilage matrix macromolecules, the expression of the differentially spliced form of type II procollagen mRNA (IIA), and specifically the co-localization of types II and X collagen in the developing antler tip. Taken together, they strongly indicate that antler growth involves an endochondral process.

Direct sequencing of PCR products derived from cDNAs for the pro alpha 1 and pro alpha 2 chains of type I procollagen as a screening method to detect mutations in patients with osteogenesis imperfecta

More than 150 mutations in the genes for type I procollagen have been found in unrelated patients with osteogenesis imperfecta (OI), but mutations have been difficult to define in many patients with the mildest forms of the disease. Here, we have used robotically automated sequencing of the cDNAs for type I procollagen to screen for mutations in 12 patients suspected of having nonlethal OI (types I, III, and IV). Single base mutations that changed codons for obligate glycine residues were found in seven of the patients. Altogether, we analyzed 4,379 bp of sequences of both alleles of the pro alpha 1 (I) collagen (8,758 bp of allelic sequences) and 4,200 bp of sequences of both alleles of the pro alpha 2(I) collagen (8,400 bp of allelic) from each patient.

Characterization of two genes coding for a similar four-cysteine motif of the amino-terminal propeptide of a sea urchin fibrillar collagen

We report the characterization of the 5' region of the gene coding for the 2 alpha fibrillar collagen chain of the sea urchin Paracentrotus lividus. This sequence analysis identified the intron/exon organization of the region of the gene coding for the signal peptide, the cysteine-rich domain and the 12 repeats of the four-cysteine module of the unusually long amino-propeptide. This still unknown four-cysteine motif is generally encoded by one exon, which confirms that the distinct amino-propeptide structures of the fibrillar collagens arise from the shuffling of several exon-encoding modules. Moreover, Southern-blot analysis of the sea urchin genome and sequencing of selected genomic clones allowed us to demonstrate that several sea urchin genes could potentially code for the four-cysteine module. Curiously, one of these genes lacks the exons coding for four repeats of this motif while, in another gene, the same exons are submitted to an alternative splicing event.

The detection of the mRNAs of procollagen types I, II and III in human fetal fingers by in situ hybridization using digoxigenin-labelled oligonucleotide probes

Messenger RNAs (mRNAs) encoding procollagen alpha 1 type I,alpha 1 type II and alpha 1 type III have been localized in paraffin sections of human fetal fingers using digoxigenin-labelled synthetic oligonucleotide probes. The probe-mRNA hybrids were visualized using an anti-digoxin antibody amplified with sandwich techniques. These protocols provided an excellent hybridization signal with minimal background noise. The sensitivity of the protocols was nearly equivalent to that seen when using isotopic cDNA probes. In human fetal fingers, intense hybridization signals for procollagen alpha 1 type I mRNA were detected in the osteoblasts and the fibroblasts of periosteum and perichondrium, the tenocytes of tendons, fibroblasts of ligaments, the synovial membrane and deeper layers of the dermis. In contrast, positive hybridization signals for procollagen alpha 1 type II mRNA were visualized in chondrocytes and the cambial layer of perichondrium. The signals for procollagen alpha 1 type III mRNA were detected in the fibroblasts of the dermis and perichondrium. The probes which have lower melting temperatures (Tm) could not detect the corresponding mRNAs.

The mouse type-III procollagen-encoding gene: genomic cloning and complete DNA sequence

Overlapping cosmid clones were isolated that covered the entire mouse type-III collagen-encoding gene (mCol3) locus including flanking sequences approximately 40 kb upstream and 20 kb downstream from the gene. This gene was characterized initially by restriction mapping and then followed by sequencing of 43.6 kb, including 5 kb upstream from the transcription start point (tsp) and all exons and introns of the entire gene. The optimal parameters for sequencing a gene of this size were determined by sequencing 5-10-kb fragments at different ratios of random and directed sequencing, and comparing their efficiency. Based on our experience for sequencing mCol3, we have estimated that the most cost-efficient method was to achieve a twofold redundancy in sequencing by using random DNA subclones as templates for sequencing prior to initiating directed DNA sequencing to close the gaps between contiguous regions. mCol3 spans 37.6 kb from the tsp to the single polyadenylation site and contains 51 exons. The overall structure of mCol3 is similar to that of other members of the fibrillar collagen-encoding gene family. Several repetitive elements were located within the gene boundaries. Based on the nucleotide (nt) sequence, the predicted sizes of the mouse type-III collagen (mCOL3) mRNA and polypeptide are 4767 nt and 1464 amino acids (aa), respectively. A comparison of mCOL3 versus the human type-III collagen (hCOL3) showed 91% identity at the aa level.

A 5' splice site mutation affecting the pre-mRNA splicing of two upstream exons in the collagen COL1A1 gene. Exon 8 skipping and altered definition of exon 7 generates truncated pro alpha 1(I) chains with a non-collagenous insertion destabilizing the triple helix

A heterozygous de novo G to A point mutation in intron 8 at the +5 position of the splice donor site of the gene for the pro alpha 1(I) chain of type I procollagen, COL1A1, was defined in a patient with type IV osteogenesis imperfecta. The splice donor site mutation resulted not only in the skipping of the upstream exon 8 but also unexpectedly had the secondary effect of activating a cryptic splice site in the next upstream intron, intron 7, leading to re-definition of the 3' limit of exon 7. These pre-mRNA splicing aberrations cause the deletion of exon 8 sequences from the mature mRNA and the inclusion of 96 bp of intron 7 sequence. Since the mis-splicing of the mutant allele product resulted in the maintenance of the correct codon reading frame, the resultant pro alpha 1(I) chain contained a short non-collagenous 32-amino-acid sequence insertion within the repetitive Gly-Xaa-Yaa collagen sequence motif. At the protein level, the mutant alpha 1(I) chain was revealed by digestion with pepsin, which cleaved the mutant procollagen within the protease-sensitive non-collagenous insertion, producing a truncated alpha 1(I). This protease sensitivity demonstrated the structural distortion to the helical structure caused by the insertion. In long-term culture with ascorbic acid, which stimulates the formation of a mature crosslinked collagen matrix, and in tissues, there was no evidence of the mutant chain, suggesting that during matrix formation the mutant chain was unable to stably incorporated into the matrix and was degraded proteolytically.

Specific inhibition of expression of a human collagen gene (COL1A1) with modified antisense oligonucleotides. The most effective target sites are clustered in double-stranded regions of the predicted secondary structure for the mRNA

A series of antisense oligonucleotides (ASOs) were synthesized and tested to define the best target sites within an RNA transcript of collagen for effective inhibition of expression. The test system consisted of mouse NIH 3T3 fibroblasts that were stably transfected with a human minigene for procollagen I so that the cells simultaneously synthesized full-length mouse pro alpha 1 (I) chains and internally deleted human pro alpha 1 (I) chains. The sequences of the transcripts from both genes were compared, and a series of 28 ASOs were designed to target sites in which there were at least two base differences within a 20-nucleotide sequence between the human and mouse transcripts. Six of the ASOs specifically decreased the levels of pro alpha 1 (I) chain synthesized from the human gene without a decrease in the levels of pro alpha 1 (I) chains from the mouse endogenous gene. The most effective ASOs reduced the intracellular levels of human pro alpha 1 (I) chains relative to the mouse pro alpha 1 (I) chains to 37-67% of the control values. Combined addition of two effective ASOs or a second administration of the same effective ASO did not produce any additive effect. The results did not support previous suggestions that the best target sites for ASOs were sequences around initiation codons for translation, at intron-exon boundaries, or in single-stranded loops in hairpin structures. Also, the results did not support previous suggestions that the most effective ASOs are those with the highest affinities for their target sequences. Instead, the most consistent pattern in the data was that the most effective ASOs were those targeted to sequences that were predicted to form clustered double-stranded structures in RNA transcripts.

In situ expression of collagen and proteoglycan genes in notochord and during skeletal development and growth

Cartilage is an important tissue in skeletogenesis, in the growth of long bones, and as a flexible component of the mature skeleton. The extracellular matrix proteins type II collagen and aggrecan comprise 90% of the matrix and are characteristic of cartilage. Type II collagen provides structural integrity to the tissue, while aggrecan confers resiliency. The quantity of type II procollagen is controlled at the level of transcription of mRNA from the COL2A1 gene. In addition, type II procollagen can be expressed in two isoforms by differential splicing of the primary gene transcript, a post-transcriptional control mechanism. The two mRNAs either include exon 2 (type IIA) or exclude exon 2 (type IIB) which encodes the major portion of the amino (NH2)-propeptide [Ryan and Sandell (1990), J. Biol. Chem., 265:10334-10339]. The aggrecan gene also encodes alternative splice forms that may be developmentally expressed. The regulation of aggrecan splicing or transcription has not been studied in detail. To determine the spatial and temporal patterns of expression of extracellular matrix in the development of cartilage, we have examined the expression of type II collagen and aggrecan during chondrogenesis in the vertebral column and during elongation of a newborn growth plate. Our results indicate that there is a developmental sequence of type II collagen splice form expression during chondrogenesis with type IIA expressed in prechondrocytes and type IIB expressed in chondrocytes. During elongation of the growth plate, mature chondrocytes express type IIB procollagen and then differentiate into hypertrophic chondrocytes and initiate expression of type X collagen. In all cases, aggrecan was coordinately expressed with type IIB procollagen. As cartilage-like proteins have been observed in more primitive structures such as notochord, the expression of type II collagen mRNAs was also examined in the notochordal remnants of the vertebral column. In the notochord, the predominant collagen expressed was the type IIA collagen prechondrocyte isoform. Notochordal cells also expressed mRNAs more characteristic of fibroblasts such as versican and decorin: low expression of type I collagen, type IIB collagen, and aggrecan were observed.

Partial rescue of a lethal phenotype of fragile bones in transgenic mice with a chimeric antisense gene directed against a mutated collagen gene

Previously, transgenic mice were prepared that developed a lethal phenotype of fragile bones because they expressed an internally deleted mini-gene for the pro alpha 1(I) chain of human type I procollagen. The shortened pro alpha 1(I) chains synthesized from the human transgene bound to and produced degradation of normal pro alpha 1(I) chains synthesized from the normal mouse alleles. Here we assembled an antisense gene that was similar to the internally deleted COL1A1 minigene but the 3' half of the gene was inverted so as to code for an antisense RNA. Transgenic mice expressing the antisense gene had a normal phenotype, apparently because the antisense gene contained human sequences instead of mouse sequences. Two lines of mice expressing the antisense gene were bred to two lines of transgenic mice expressing the mini-gene. In mice that inherited both genes, the incidence of the lethal fragile bone phenotype was reduced from 92% to 27%. The effects of the antisense gene were directly demonstrated by an increase in the ratio of normal mouse pro alpha 1(I) chains to human mini-pro alpha 1(I) chains in tissues from mice that inherited both genes and had a normal phenotype. The results raise the possibility that chimeric gene constructs that contain intron sequences and in which only the second half of a gene is inverted may be particularly effective as antisense genes.

The clinical features of Ehlers-Danlos syndrome type VIIB resulting from a base substitution at the splice acceptor site of intron 5 of the COL1A2 gene

The features of a 32 year old woman with Ehlers-Danlos syndrome type VIIB and affected members of her family, resulting from a mutation in one COL1A2 allele, were studied. Her dermal type I collagen contained alpha 2(I) chains and mutant pN-alpha 2(I) chains in which the amino-terminal propeptide remained attached to the alpha 2(I) chain. She was heterozygous for an AG-->AC mutation at the splice acceptor site of intron 5 of the COL1A2 gene. The mutation activated a cryptic AG splice acceptor site corresponding to positions +14 and +15 of exon 6 of the COL1A2 gene. In contrast to previous reports only five, rather than all 18, amino acids encoded by exon 6 were deleted in the proband. The deleted peptide removed the amino-proteinase cleavage site, but not the nearby lysine cross linking site in the amino-telopeptide of the alpha 2(I) chain. She was born with bilateral hip dislocations, knee subluxations, and generalised joint hypermobility. Bilateral inguinal herniae and an umbilical hernia were present at birth. Facial features included a depressed nasal bridge with prominent paranasal folds. The skin was soft, moderately hyperelastic, and sagged over the face. Skin fragility and easy bruising were apparent from childhood. Skin wounds healed slowly and with broad, paper thin scars. Throughout her life, she had multiple fractures of the small bones of her hands and feet following moderate trauma. Electron microscopy of the proband's dermis as well as deep fascia and hip joint capsule from her affected brother showed that collagen fibrils in transverse section were nearly circular but with irregular margins. Light microscopy of bone from her affected brother and son showed normal Haversian systems and lamellar bone. All of these tissues contained approximately equal amounts of the normal and mutant alpha2(I) chains. The findings of this study confirm that loss of the amino-proteinase cleavage site of the pro alpha2(I) collagen chains, owing to anomalous splicing of exon 6 sequences in the conversion of pre-mRNA to mRNA, produces the clinical features of Ehlers-Danlos syndrome type VIIB. The history of frequent fractures found in this family is atypical and indicates an overlap with osteogenesis imperfecta.

Synthesis of recombinant human procollagen II in a stably transfected tumour cell line (HT1080)

Apparently because the biosynthetic pathways involve eight or more highly specific post-translational enzymes, it has been difficult to obtain expression of genes for fibrillar collagens in recombinant systems. Here two constructs of the human gene for procollagen II (COL2A1) were prepared, one with about 0.5 kb of a promoter for a procollagen I gene (COL1A1) and the other with about 4 kb of the promoter for the procollagen II gene. The constructs, together with a neomycin-resistant gene, were transfected into a human tumour cell line (HT1080) that synthesizes the collagen IV found in basement membranes, but does not synthesize any fibrillar collagen. About two per 100 clones resistant to the neomycin analogue G418 synthesized and secreted human procollagen II. Milligram quantities of the recombinant procollagen II were readily isolated from the cultured medium. The recombinant procollagen II had the expected amino acid sequence as defined by nucleotide sequencing of mRNA-derived cDNA and the expected amino acid composition as defined by analysis of procollagen II that was converted into collagen II by digestion with procollagen N- and C-proteinases. Also, analysis of the carbohydrate content indicated that there was glycosylation of some of the hydroxylysine residues but no evidence of post-translational overmodification of the residues. In addition, the protein was shown to have a native conformation as assayed by a series of protease digestions. No essential differences were found between clones transfected with the COL2A1 gene construct containing the COL1A1 promoter and the similar construct containing the COL2A1 promoter in terms of number of clones synthesizing recombinant procollagen II and the levels of expression. With both constructs, the expression of the COL2A1 gene was closely related to copy number. The results demonstrated therefore that it is not essential to use a promoter for a gene normally expressed in a host cell in order to obtain gene copy-number-dependent expression of an exogenous collagen gene in stably transfected cells.

Collagen genes: mutations affecting collagen structure and expression

It is to be expected that more collagen genes will be identified and that additional heritable connective tissue diseases will be shown to arise from collagen mutations. Further progress will be fostered by the coordinated study of naturally occurring and induced heritable connective tissues diseases. In some instances, human mutations will be studied in more detail using transgenic mice, while in others, transgenic studies will be used to determine the type of human phenotype that is likely to result from mutations of a given collagen gene. Further studies of transcriptional regulation of the collagen genes will provide the prospect for therapeutic control of expression of specific collagen genes in patients with genetically determined collagen disorders as well as in a wide range of common human diseases in which abnormal formation of the connective tissues is a feature.

Expression of collagens I, II, X, and XI and aggrecan mRNAs by bovine growth plate chondrocytes in situ

The cells responsible for skeletal growth are the chondrocytes of the cartilaginous growth plate. These cells differentiate through a series of maturational stages, establishing different zones in the growth plate. Among the major functions of these cells is the production of appropriate extracellular matrix, primarily composed of collagens and proteoglycans. To determine whether matrix synthesis varies with respect to maturational stage and in which cell populations different collagens are expressed, bovine growth plates were analyzed by in situ hybridization to mRNA and by Northern blot hybridization. The most abundant collagen mRNA in the growth plate was type-II collagen. This mRNA was present at relatively low levels in the most immature cells of the growth plate but increased several-fold as cells entered the proliferative stage and remained high through subsequent phases of maturation. Type-XI collagen mRNA and mRNA for the cartilage-characteristic proteoglycan, aggrecan, were codistributed with the type-II collagen mRNA; however, both were present in much smaller quantities. Type-X procollagen mRNA was localized to chondrocytes late in their maturation and was expressed at levels similar to the expression of type-II collagen. In situ hybridization of serial sections revealed that growth plate chondrocytes in their more mature stages contain both type-II and type-X collagen mRNA. Type-I collagen mRNA was not observed in growth plate chondrocytes at any maturational stage; rather, it was localized to a morphologically distinct population of cells attached to calcifying cartilage septa in the region of vascular invasion.(ABSTRACT TRUNCATED AT 250 WORDS)

Genomic sequence of mouse COL1A1 encoding the collagen propeptides

The nucleotide sequences of the mouse pro alpha 1(I) gene regions coding for the N- and C-propeptides is reported. The exon-intron structure was highly homologous to human COL1A1 and the deduced amino acid sequences of the N- and C-propeptides showed 67% and 91% identity with the human sequence. This gene sequence information will allow the production of specific gene mutations by site-directed mutagenesis to study the structure and function of these important propeptide domains.

A cysteine for glycine substitution at position 175 in an alpha 1 (I) chain of type I collagen produces a clinically heterogeneous form of osteogenesis imperfecta

The molecular basis for Osteogenesis Imperfecta in a large kindred with a highly variable phenotype was identified by sequencing the mutant pro alpha 1 (I) protein, cDNA and genomic DNA from the proband. Fibroblasts from different affected individuals all synthesize both normal Type I procollagen molecules and abnormal Type I procollagen molecules in which one or both pro alpha 1 (I) chain(s) contain a cysteine residue within the triple helical domain. Protein studies of the proband localized the mutant cysteine residue to the alpha 1 (I) CB 8 peptide. We now report that cysteine has replaced glycine at triple helical residue 175 disrupting the invariant Gly-X-Y structural motif required for perfect triple helix formation. The consequences include post-translational overmodification, decreased thermal stability, and delayed secretion of mutant molecules. The highly variable phenotype in the present kindred cannot be explained solely on the basis of the cysteine for glycine substitution but will require further exploration.

Homology-mediated recombination between type I collagen gene exons results in an internal tandem duplication and lethal osteogenesis imperfecta

It has been proposed that the structure of the exons that encode the triple helical domain of the fibrillar collagen genes arose by repeated tandem duplication of an ancestral unit exon. Because these exons encode a repeat motif [(Gly-X-Y)n], sequence homology between exons may have driven the recombinational process. We have characterized a tandem duplication mutation within a COL1A1 allele of type I collagen from an infant with the lethal form of osteogenesis imperfecta. The structure of the mutation is consistent with the occurrence of an unequal crossover within a 15 base pair region of sequence identity between exons 14 and 17 of the COL1A1 gene. The recombination produced a new 81 base pair 17/14 hybrid exon and complete duplication of exons 15 and 16. The sequence implies duplication of 60 amino acid residues within the triple helical domain with preservation of the Gly-X-Y repeat. These data suggest that a recombinational mechanism that explains the hypothetical evolutionary process is active in cells, but the lethal effect of this mutation raises questions about the role of these events in creating new structures for polymeric proteins.

Completion of the last half of the structure of the human gene for the Pro alpha 1 (I) chain of type I procollagen (COL1A1)

The nucleotide sequences of the 3'-half of the human gene for the pro alpha(I) chain of type I procollagen (COL1A1) is presented. The results provide the nucleotide sequences for 26 introns not previously analyzed. The sequences that are presented, together with those previously published, make it possible to design primers for the polymerase chain reaction for amplifying and sequencing the gene. The availability of such primers will greatly facilitate the current search for mutations that can cause common and rare diseases of connective tissue.

Feedback regulation of collagen gene expression: a Trojan horse approach

The mechanisms involved in feedback regulation of type I procollagen synthesis by the N-terminal propeptide of the pro alpha 1(I) chain, termed Col 1, are poorly understood. We have constructed a metallothionein-human collagen chimeric minigene (pMTCol) that codes for a Col 1 fusion protein but lacks a signal peptide sequence and, therefore, would be expected to direct the synthesis of the fusion protein to the cytosol. Baby hamster kidney cells and fetal calf ligament cells, transfected with pMTCol, transcribed the gene and synthesized an intracellular antigen that was identified as the fusion protein with a monospecific antibody. Transfected fetal calf ligament fibroblasts showed significantly reduced levels of endogenously produced type I collagen, as determined by imaging and digital quantitation of immunofluorescence by confocal microscopy; synthesis of fibronectin, thrombospondin, and SPARC (secreted protein, acidic and rich in cysteine) was unchanged or increased in these cells. This recombinant approach offers the potential for a systematic analysis of feedback regulation of collagen synthesis.

Alternatively spliced type II procollagen mRNAs define distinct populations of cells during vertebral development: differential expression of the amino-propeptide

Type II collagen is a major component of cartilage providing structural integrity to the tissue. Type II procollagen can be expressed in two forms by differential splicing of the primary gene transcript. The two mRNAs either include (type IIA) or exclude (type IIB) an exon (exon 2) encoding the major portion of the amino (NH2)-propeptide (Ryan, M. C., and L. J. Sandell. 1990. J. Biol. Chem. 265:10334-10339). The expression of the two procollagens was examined in order to establish a potential functional significance for the two type II procollagen mRNAs. First, to establish whether the two mRNAs are functional, we showed that both mRNAs can be translated and the proteins secreted into the extracellular environment. Both proteins were identified as type II procollagens. Secondly, to test the hypothesis that differential expression of type II procollagens may be a marker for a distinct population of cells, specific procollagen mRNAs were localized in tissue by in situ hybridization to oligonucleotides spanning the exon junctions. Embryonic vertebral column was chosen as a source of tissue undergoing rapid chondrogenesis, allowing the examination of a variety of cell types related to cartilage. In this issue, each procollagen mRNA had a distinct tissue distribution during chondrogenesis with type IIB expressed in chondrocytes and type IIA expressed in cells surrounding cartilage in prechondrocytes. The morphology of the cells expressing the two collagen types was distinct: the cells expressing type IIA are narrow, elongated, and "fibroblastic" in appearance while the cells expressing type IIB are large and round. The expression of type IIB appears to be correlated with abundant synthesis and accumulation of cartilagenous extracellular matrix. The expression of type IIB is spatially correlated with the high level expression of the cartilage proteoglycan, aggrecan, establishing type IIB procollagen and aggrecan as markers for the chondrocyte phenotype. Transcripts of type II collagen, primarily type IIA, are also expressed in embryonic spinal ganglion. While small amounts of type II collagen have been previously detected in noncartilagenous tissues, the detection of this new form of the collagen in relatively high abundance in embryonic nerve tissue is unique. Taken together, these findings imply a potential functional difference between type IIA and type IIB procollagens and indicate that the removal of exon 2 from the pre-mRNA, and consequently the NH2-propeptide from the collagen molecule, may be an important step in chondrogenesis. In addition, type II procollagen, specifically type IIA, may function in noncartilage tissues, particularly during development.