Human type I procollagen genes are located on different chromosomes

Elevated Alpha 1(I) to Alpha 2(I) Collagen Ratio in Dermal Fibroblasts Possibly Contributes to Fibrosis in Systemic Sclerosis

Systemic sclerosis (SSc) is characterized by excessive collagen deposition in the skin and internal organs. Activated fibroblasts are the key effector cells for the overproduction of type I collagen, which comprises the α1(I) and α2(I) chains encoded by COL1A1 and COL1A2, respectively. In this study, we examined the expression patterns of α1(I) and α2(I) collagen in SSc fibroblasts, as well as their co-regulation with each other. The relative expression ratio of COL1A1 to COL1A2 in SSc fibroblasts was significantly higher than that in control fibroblasts. The same result was observed for type I collagen protein levels, indicating that α2(I) collagen is more elevated than α2(I) collagen. Inhibition or overexpression of α1(I) collagen in control fibroblasts affected the α2(I) collagen levels, suggesting that α1(I) collagen might act as an upstream regulator of α2(I) collagen. The local injection of COL1A1 small interfering RNA in a bleomycin-induced SSc mouse model was found to attenuate skin fibrosis. Overall, our data indicate that α2(I) collagen is a potent regulator of type I collagen in SSc; further investigations of the overall regulatory mechanisms of type I collagen may help understand the aberrant collagen metabolism in SSc.

In Situ Cytokine Expression and Morphometric Evaluation of Total Collagen and Collagens Type I and Type III in Keloid Scars

Keloids are characterized by excessive collagen deposition and growth beyond the edges of the initial injury, and cytokines may be related to their formation. The objective of this study was to evaluate the collagen fibers, analyze in situ expression of cytokines in keloid lesions, and compare to the control group. Results showed that there was a predominance of women and nonwhite and direct black ancestry. Keloid showed a significant increase in total and type III collagen. Significantly, the expression of mRNA for TGF-β in keloid was increased, the expressions of IFN-γ, IFN-γR1, and IL-10 were lower, and IFN-γR1 and TNF-α had no statistical difference. Correlations between collagen type III and TGF-β mRNA expression were positive and significant, IFN-γ, IFN-γR1, and IL-10 were negative and significant, and TNF-α showed no statistical difference. We conclude that there was a significant increase of total collagen in keloid and predominance of collagen type III compared to the controls, showing keloid as an immature lesion. There is a significant increase in TGF-β mRNA in keloid lesions, and a significant decrease in IFN-γ and IL-10, suggesting that these cytokines are related to keloid lesions.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Investigation of the Sp1-binding site polymorphism within the COL1A1 gene in participants with Achilles tendon injuries and controls

Sequence variants within the type V collagen (COL5A1) and tenascin C (TNC) genes have to date been shown to be associated with chronic Achilles tendinopathies and/or spontaneous Achilles tendon ruptures. Type V collagen and tenascin C are quantitatively minor components of tendon, while type I collagen is the major structural component. There is increased expression of the COL1A1 gene, which encodes for the alpha1 chain of type I collagen, in the painful Achilles tendon. A functional Sp1-binding site polymorphism (SNP rs1800012; IVS1+1023G>T) within this gene has been shown to be associated with several connective tissue disorders. The aim of this study was to determine whether the Sp1-binding site polymorphism within the COL1A1 gene is associated with chronic Achilles tendinopathies and/or spontaneous Achilles tendon ruptures. Achilles tendinopathy (n=85), Achilles rupture (n=41) and asymptomatic control (n=125) participants were genotyped for the COL1A1 Sp1-binding site polymorphism. There were no observed statistical differences in the genotype (p=0.602) or allele (p=0.694) distributions between the groups. In conclusion, this study has shown that there is no association between the Sp1-binding site polymorphism within the first intron of COL1A1 and Achilles tendinopathy or Achilles tendon rupture within the population studied.

Transcriptional activation of the type I collagen genes COL1A1 and COL1A2 in fibroblasts by interleukin-4: analysis of the functional collagen promoter sequences

Pneumonitis followed by lung fibrosis is a frequent complication of radiation therapy of chest tumors. A hallmark of these fibrotic lesions is the excessive production and accumulation of extracellular matrix proteins such as type I collagen. In addition to TGF-beta1, IL-4 has been recognized as a potent inducer of collagen gene synthesis in fibroblasts. In this study, we analyzed the regulation of the alpha1(I) procollagen (COL1A1) promoter and the alpha2(I) procollagen (COL1A2) promoter by IL-4 in normal human lung fibroblasts. We provide evidence that the IL-4-induced transcriptional activator STAT6 binds to various sequences within the COL1A1 and COL1A2 promoter. The regulatory function of these regions was tested by reporter gene analysis using 5' deletions of the COL1A1 and COL1A2 promoter fused to the luciferase gene. Interleukin-4 treatment of human fibroblasts transiently transfected with COL1A1 promoter deletion constructs resulted in luciferase activity exceeding that of untreated fibroblasts by 25%, while luciferase activity driven by the COL1A2 promoter was enhanced by about 70% upon IL-4 treatment. A combined action of SP1, NFkappaB, and STAT6 essentially contributes to the IL-4 mediated COL1A2 gene activation. An AP2 site adjacent to the reverse orientated STAT6 consensus motif TTC N(3/4) GCT is located within 205 bases from the transcription start site and seems to support the moderate IL-4-induced COL1A1 gene activation. Interferon-gamma downregulation of transcription is mainly seen with the COL1A1 promoter.

Radiation hybrid mapping of the canine type I and type IV collagen gene subfamilies

We are interested in the collagen gene superfamily and its involvement in hereditary diseases of the human and domestic dog. Presented here is radiation hybrid mapping of the type I and type IV collagen gene subfamilies on the most recent version of the canine map. The col1A1 gene was mapped to chromosome 9, col1A2 was mapped to chromosome 14, col4A1 and col4A2 were mapped to chromosome 22 and col4A3 and col4A4 were mapped to chromosome 25. The col4A5 and col4A6 genes, while linked to one another, are not linked in the present version of the canine map but likely are present on the X chromosome. These data provide an insight into the molecular evolution of these subfamilies and increase the number of mapped genes in discrete regions of the canine genome.

Elastic tissue abnormalities resembling pseudoxanthoma elasticum in beta thalassemia and the sickling syndromes

The development of clinical and histopathologic manifestations of a diffuse elastic tissue defect, resembling inherited pseudoxanthoma elasticum (PXE), has been encountered with a notable frequency in patients with beta thalassemia, sickle cell disease, and sickle thalassemia. The PXE-like clinical syndrome, consisting of skin, ocular, and vascular manifestations, has a variable severity in these hemoglobinopathies and it is age-dependent, with a generally late onset, after the second decade of life. The defect is believed to be acquired rather than inherited and related to the consequences of the primary disease. The high prevalence of the findings implicates the elastic tissue injury as one of the main comorbid abnormalities encountered in beta thalassemia and the sickling syndromes. In these patients a number of complications, sometimes serious, has been recognized to be related to ocular and vascular elastic tissue defects. Because several organ systems are involved, each medical specialty should be aware of the phenomenon. This coexistence, on the other hand, introduces a novel pathogenetic aspect of PXE and an important research challenge.

The genetic basis of the osteochondrodysplasias

The osteochondrodysplasias are a heterogeneous group of disorders characterized by abnormal growth and remodeling of cartilage and bone, affecting from 2 to 4.7 per 10,000 individuals. Most osteochondrodysplasias are heritable and many have elaborate patterns of genetic transmission. Affected individuals generally require management by multidisciplinary teams of specialists. In this review, we divide the osteochondrodysplasias into groups based on their genetic relationships, including mutations in various types of collagen, fibroblast growth factor, cartilage oligomeric matrix protein, parathyroid hormone receptor, the diastrophic dysplasia sulfate transporter, enzymes such as steroid sulfatases, transcription factor SOX9, and a cysteine proteinase, cathepsin K. We describe the major osteochondrodysplasias, define their causes and clinical manifestations, and provide the orthopaedic surgeon with an understanding of the underlying molecular defects as well as the anatomical aspects of these disorders.

Estradiol suppresses mesangial cell type I collagen synthesis via activation of the MAP kinase cascade

We have previously shown that estradiol suppresses the synthesis of type I collagen by murine mesangial cells grown in the presence of serum via activation of the transcription factor activator protein-1 (AP-1). We hypothesized that estradiol upregulates AP-1 via activation of the mitogen-activated protein (MAP) kinase cascade, a signal transduction pathway that regulates AP-1 activity. Estradiol (10(-10) to 10(-7) M) upregulated the MAP kinase pathway in murine mesangial cells grown in the presence of serum in a dose-dependent manner. Activation was evident by 1 min, peaked at 10 min, and was completely dissipated by 2 h. In contrast, estradiol had no significant effect on total (phosphorylated + unphosphorylated) p44 extracellular signal-related protein kinase (ERK) or p42 ERK. Nuclear extracts isolated from mesangial cells treated with estradiol showed increased binding to a consensus sequence AP-1 binding oligonucleotide in gel shift assays. In contrast, nuclear extracts from cells exposed to PD-98059, a highly selective inhibitor of MAP kinase-ERK kinase 1 (MEK1) and MEK2, showed reduced binding. In addition, PD-98059 antagonizes the enhanced binding induced by estradiol. Estradiol (10(-9) M) suppressed mesangial cell type I collagen synthesis (37.8 +/- 2.4%, expressed as a percentage of control values, P < 0.001 vs. control). In contrast, PD-98059 increased type I collagen synthesis (344.6 +/- 98.8, P < 0.01) and reversed the suppression of type I collagen synthesis induced by estradiol. The effects of estradiol, PD-98059, and PD-98059 plus estradiol on type I collagen protein synthesis were closely paralleled by their effects on steady-state levels of mRNA for the alpha(1) chain of type I collagen. These data suggest that estradiol suppresses type I collagen synthesis via upregulation of the MAP kinase cascade, leading to stimulation of AP-1 activity.

Arterial calcifications in beta-thalassemia

The purpose of this study was to define the incidence of arterial calcifications in patients with beta-thalassemia. Beta-thalassemia patients have been shown to present a high prevalence of angioid streaks and skin lesions characteristic of pseudoxanthoma elasticum (PXE). Given the fact that vascular involvement in the form of arterial calcifications is also a common manifestation of PXE, the authors investigated radiographically the presence of arterial calcifications in beta-thalassemia patients. They studied 40 patients with beta-thalassemia over 30 years of age. Forty healthy, age- and sex-matched subjects were chosen as a control group. Radiographs of the tibias were performed in order to disclose arterial calcifications. The occurrence of PXE skin lesions and of angioid streaks (AS) was also investigated. Arterial calcifications were detected in the posterior tibial artery in 22 (55%) beta-thalassemia patients and in six (15%) controls (P < 0.01 for the comparison). PXE skin lesions and AS were found in eight (20%) and 21 (52%) patients respectively. A total of 34 patients (85%) had at least one of the three lesions, namely, arterial calcifications, angioid streaks, and/or PXE-like skin lesions. Stepwise logistic regression analysis did not reveal prognostic value in independent variables such as transfusions, chelation therapy, pseudoxanthoma elasticum skin lesions and/or angioid streaks, diabetes, hemoglobin, serum ferritin, and uric acid. It was concluded that arterial calcifications are common in older beta-thalassemia patients. This finding could be a manifestation of an acquired PXE syndrome associated with beta-thalassemia, and consequently, vascular events complicating PXE should be expected in these patients.

Ribozymes: structure, function, and potential therapy for dominant genetic disorders

Some dominant genetic disorders, viral processes and neoplastic disorders base their pathogenicity on the production of protein or proteins that negatively affect cellular metabolism or environment. Thus, the inhibition of the synthesis of those proteins should prevent the biological damage. A promising approach to decreasing the level of the abnormal protein(s) is represented by specific interference with gene expression at the level of mRNA. The specific suppression of the expression of an mRNA can be achieved by using ribozymes. Ribozymes are RNA molecules able to break and form covalent bonds within a nucleic acid molecule. These molecules, with even greater potential advantages than antisense oligodeoxynucleotides, are able to bind specifically and cleave an mRNA substrate. There are advantages to using ribozymes instead of antisense oligodeoxynucleotides. Ribozymes can inactivate the target RNA without relying on the host cell's machinery and they have the capacity to cleave more than one copy of the target RNA by dissociating from the cleavage products and binding to another target molecule. Most of the studies performed to date have described the use of ribozymes as therapeutic agents for viral and cancer diseases. However, some dominant genetic disorders may also benefit from this approach. This is the case for some connective tissue disorders such as osteogenesis imperfecta, Marfan syndrome and the craniosynostotic syndromes.

Regulation of lysyl oxidase by basic fibroblast growth factor in osteoblastic MC3T3-E1 cells

Lysyl oxidase catalyzes the final known enzymatic step required for collagen and elastin cross-linking. A cross-linked collagenous extracellular matrix is required for bone formation. This study investigated whether lysyl oxidase, like its type I collagen substrate, is down-regulated by basic fibroblast growth factor (bFGF) in osteoblastic MC3T3-E1 cells and determined the degree of post-transcriptional control. Steady-state lysyl oxidase mRNA levels decreased to 30% of control after 24 h of treatment with 1 and 10 nm bFGF. This regulation was time-dependent. COL1A1 mRNA levels declined to less than 10% of control after 24 h of bFGF treatment. Media lysyl oxidase activity decreased consistent with steady-state mRNA changes in cultures that were refed after 24 h of growth factor treatment. Interestingly, treatment of MC3T3-E1 cells with 0.01-0.1 nm bFGF for 24 h and treatment with 1 nm bFGF for up to 12 h resulted in a modest stimulation of lysyl oxidase gene expression and enzyme activity. At least 50% of the down-regulation of lysyl oxidase was shown to be posttranscriptional. New protein synthesis was not required for the down-regulation by bFGF, but cycloheximide did increase constitutive lysyl oxidase mRNA levels 2.5-fold. We conclude that lysyl oxidase and COL1A1 are regulated similarly by bFGF in these osteoblastic cells, consistent with the in vivo effects of this growth factor on bone collagen metabolism.

Pre- and post-translational regulation of lysyl oxidase by transforming growth factor-beta 1 in osteoblastic MC3T3-E1 cells

The final enzymatic step required for collagen cross-linking is the extracellular oxidative deamination of peptidyl-lysine and -hydroxylysine residues by lysyl oxidase. A cross-linked collagenous extracellular matrix is required for bone formation. The goals of this study were to compare the transforming growth factor (TGF)-beta 1 regulation of lysyl oxidase enzyme activity and steady state mRNA levels to changes in COL1A1 mRNA levels in MC3T3-E1 osteoblastic cells. TGF-beta 1 increased steady state lysyl oxidase and COL1A1 mRNA levels in a dose- and time-dependent manner. The increase in lysyl oxidase mRNA levels was transient, peaking at 12 h and 8.8 times controls in cells treated with 400 pM TGF-beta 1. COL1A1 steady state mRNA levels increased maximally to 3.5-fold of controls. Development of increased lysyl oxidase enzyme activity was delayed and was of slightly lower magnitude than the increase in its mRNA levels. This suggested limiting post-translational processing of lysyl oxidase proenzyme. Pulse-labeling/immunoprecipitation studies demonstrated slow proenzyme secretion and proteolytic processing. Development and application of an independent assay for lysyl oxidase proenzyme proteolytic processing activity verified its proportionately lower stimulation by 400 pM TGF-beta 1. Thus, lysyl oxidase regulation by TGF-beta 1 in osteoblastic cell cultures occurs at both pre- and post-translational levels. This regulation is consistent with increased production of a collagenous extracellular matrix.

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.

Pseudoxanthoma elasticum-like skin lesions and angioid streaks in beta-thalassemia

One hundred patients with homozygous or doubly heterozygous beta-thalassemia (62 with the major form and 38 with beta-thalassemia intermedia) were examined for signs of Pseudoxanthoma elasticum (PXE). Diagnostic skin lesions were found in 16 patients with either form of the basic disease. Twenty percent of all patients had angioid streaks (AS); both PXE skin lesions and AS were found in 10% of the patients; in all, 26% had either one or both of these manifestations. A positive correlation was found between the presence of one or both types of lesion and age of the patients (P = 0.032); there were no differences as regards ferritin and hematocrit levels, number of transfused units, chelation therapy, and splenic status between patients with PXE/AS findings and those without. The pathogenesis of these connective tissue manifestations at such a high frequency in beta-thalassemia is not clear; the possibilities of it's being acquired or inherited are discussed, the former being considered to be the more economical interpretation.

Expression of type I collagen pro-alpha 2 chain mRNA in adult human permanent teeth as revealed by in situ hybridization

The expression of the gene COL1A2, coding for the pro-alpha 2 chain of type I pro-collagen, was analyzed in fully developed human permanent teeth. The teeth were fixed with formalin, demineralized with EDTA for about ten weeks, and embedded in paraffin. Pro-alpha 2(I) mRNA was localized in the sections by in situ hybridization, with use of [35S)]-labeled single-stranded RNA probes. The amount of mRNA for pro-alpha 2(I) collagen chain, as indicated by the relative densities of silver grains and the grain counts per cell in autoradiography, was high in odontoblasts, whereas in pulpal fibroblasts it was low. High levels of pro-alpha 2(I)mRNA expression were also present in those odontoblasts which had elaborated new dentin matrix in response to dental caries. Expression in the periodontal ligament, including the cementoblast layer, was slightly stronger than that in odontoblasts. The intense expression of pro-alpha 2(I) mRNA in odontoblasts of adult teeth suggests that even after the completion of primary dentin formation, they continue to synthesize heterotrimeric type I collagen molecules. Cell type-specific differences in the expression of pro-alpha 2(I) mRNA imply that type I collagen probably plays a major role in the regulation of the structure and function of dental tissues. Finally, in situ hybridization enabled pro-alpha 2(I) collagen mRNA to be detected in tissue sections even after prolonged demineralization, and thus it proved to be a valuable technique for analysis of gene expression in adult dental tissues, as shown here for COL1A2.

Clinical and genetic aspects in autosomal dominant inherited osteogenesis imperfecta type I

In 30 fully investigated family pedigrees in which there were at least two generations of people suffering from osteogenesis imperfecta type I (McKusick no. 16620), the data on 144 random offspring could be used for segregation analysis. The major characteristics, blue sclerae, fractures, and hearing loss, were present in every pedigree. Their penetrance was also calculated. Precise definitions were used in the study. The segregation ratio or observed: expected ratio was 70:72. The incidence of blue sclerae was 70:70 (100%), for fractures 61:70 (87%), and for hearing loss 30:70 (43%). There was a very clear relationship between age and the progression of the hearing loss. Dividing the offspring into two groups depending on whether or not male-to-male inheritance was present and performing segregation and penetrance calculation on these data did not produce any indications that there are two genetically distinguishable subtypes of osteogenesis imperfecta type I. In a smaller group of 107 offspring, calculations could be made on several separate generations.

Pseudoxanthoma elasticum and angioid streaks in two cases of beta-thalassaemia

Two cases of beta thalassaemia with pseudoxanthoma elasticum and angioid streaks (Grönblad-Strandberg syndrome) are reported. To the best of our knowledge, this is the first report of a combination between these two genetically determined disorders. The possible theories of the pathogenesis of pseudoxanthoma elasticum and angioid streaks are discussed.

Assignment of the gene coding for the alpha-subunit of prolyl 4-hydroxylase to human chromosome region 10q21.3-23.1

Prolyl 4-hydroxylase, an alpha 2 beta 2 tetramer, catalyzes the formation of 4-hydroxyproline in collagens by the hydroxylation of proline residues in peptide linkages and plays a crucial role in the synthesis of these proteins. The gene for the beta-subunit of prolyl 4-hydroxylase has recently been mapped to the long arm of human chromosome 17, at band 17q25. We report here chromosomal localization of the gene for the catalytically and regulatorily important alpha-subunit of human prolyl 4-hydroxylase. Analysis of 24 rodent x human cell hybrids by Southern blotting with cDNA probes for the human alpha-subunit indicated complete cosegregation of the gene for the alpha-subunit with human chromosome 10. A cell hybrid containing only part of chromosome 10 mapped the gene to 10q11----qter. In situ hybridization mapped the gene to 10q21.3-23.1. The gene for the alpha-subunit is thus not physically linked to that for the beta-subunit of the enzyme.

Protein disulphide isomerase, a multifunctional endoplasmic reticulum protein

Protein disulphide isomerase (E.C. 5.3.4.1) has been purified, cloned, and sequenced from a variety of vertebrate tissues. The enzyme and its isoforms have been assigned a role in four functional activities: (1) hydroxylation of proline residues in procollagen; (2) disulphide bond oxidation, isomerization, and reduction; (3) the major non-nuclear binding protein of the thyroid hormone 3,3',5-triiodo-L-thyronine; and (4) a component of oligosaccharide transferase. The concentration of the enzyme has been shown to be positively correlated with an endoplasmic reticulum network which is active in secreting disulphide-bonded polypeptides. The enzyme is directed into the endoplasmic reticulum by virtue of a 19 residue N-terminal signal peptide; a four amino acid C-terminal KDEL sequence prevents the enzyme from being secreted. Careful inspection of the sequence data of the isoforms from human tissues reveals a 97% similarity; whereas, analyses of the data from chick tissues reveals only a 80% level of similarity. Chromosomal localizations using human cDNA probes against different human isoforms have assigned the gene(s) to opposite ends of the long arm of chromosome 17. The compiled data suggest the presence of a family of related polypeptides, all of which reside within the lumen of the endoplasmic reticulum.

Molecular mechanisms of collagen gene expression

Collagens are a structurally and functionally heterogenous group of proteins encoded by a family of genes that share evolutionary history. Collagen gene expression is regulated both in developmental, tissue-specific manners as well as in response to a variety of biologic and pharmacologic inducers. In the present review we have attempted to synthesize a conceptual overview of the available information from studies aimed at deciphering the molecular mechanisms of collagen gene expression. We have chosen to focus our discussion mainly, although not exclusively, to observations relating to type I collagen gene for a number of practical reasons. The underlying theme that emerges from this survey of the literature is that the regulation of collagen gene expression is complex, utilizing transcriptional, posttranscriptional and translational mechanisms. Although the transcriptional control mechanisms that involve activation and modulation of collagen gene transcription by RNA polymerase II appear to predominate, preferential stabilization of collagen mRNAs and modulation of translational discrimination appear to play significant roles in the regulation of collagen biosynthesis under some physiological situations. Molecular organization of the regulatory regions of collagen genes reveal a mosaic of subdomains with overlapping sequence motifs, involved in positive and negative transcriptional regulation. The precise identity of the cis-acting subdomains of the promoter/enhancer-proximal DNA of collagen gene and how they interact with the trans-acting nuclear protein(s) have yet to be elucidated and will remain the focus of future studies.

Transcription of human type I collagen genes. Variation in the relative rates of transcription of the pro alpha 1 and pro alpha 2 genes

The relative rates of transcription of the two genes for type I collagen have been measured in a runoff transcription assay using nuclei isolated from cultured human fibroblasts. Control experiments indicated that the ratio of pro alpha 1(I)/pro alpha 2(I) transcripts detected with a given nuclear preparation did not vary over a range of transcription times, nuclei concentrations, and amounts of filter-bound cDNA used in the assay. However, a significant difference in the ratio was observed when nuclei isolated from cells grown under different conditions were used. Nuclei from sub-confluent cultures generally transcribed the two genes in a ratio of 2:1 or lower, while nuclei from post-confluent cultures transcribed the genes in a much higher ratio of about 4:1. Analysis of the amount of pro alpha 1(I) and pro alpha 2(I) RNA transcribed suggests that it is the transcription of the pro alpha 1(I) gene, and not the pro alpha 2(I) gene, that varies with culture conditions. The steady state ratios of pro alpha 1(I)/pro alpha 2(I) RNA remained near 2:1 under all conditions. Thus, some post-transcriptional mechanism apparently results in maintenance of the steady-state pro alpha 1(I)/pro alpha 2(I) RNA ratios at approximately 2:1.

Chromosomal mapping of human keratin genes: evidence of non-linkage

We have determined the chromosomal location of the genes for the human keratin intermediate filament proteins K1 (type II; 67 kDa) and K10 (type I; 57 kDa) by the use of specific cDNA clones in conjunction with somatic cell hybrid analysis and in situ hybridization. The K1 keratin gene maps to chromosome region 12q11----q13; the K10 keratin gene maps to chromosome region 17q12----q21. Each gene has been mapped relative to other genes known to be localized on chromosomes 12 and 17, respectively. In somatic cell hybrid analysis, the K1 gene segregates concordantly with the Hox-3 homeo box gene cluster at chromosome region 12p12----q13. The K10 gene localizes to a region proximal to a breakpoint at 17q21 which is involved in a t(17;21)(q21;q22) translocation associated with an acute leukemia. K10 appears to be distal (telomeric) to the gene loci for G-CSF, erb-A, and Her-2, which map to chromosome region 17q12----q21. The NGFR gene and Hox-2 homeo box locus are localized distal to the 17q21 break point and thus distal to the K10 gene. These data demonstrate that keratin genes K1 and K10, which are coexpressed in terminally differentiated epidermis, are not linked in the human genome, implying the existence of trans-acting factors involved in the regulation of expression of these genes.

Construction of a genetic map of human chromosome 17 by use of chromosome-mediated gene transfer

We used somatic-cell hybrids, containing as their only human genetic contribution part or all of chromosome 17, as donors for chromosome-mediated gene transfer. A total of 54 independent transfectant clones were isolated and analyzed by use of probes or isoenzymes for greater than 20 loci located on chromosome 17. By combining the data from this chromosome-mediated gene transfer transfectant panel, conventional somatic-cell hybrids containing well-defined breaks on chromosome 17, and in situ hybridization, we propose the following order for these loci: pter-(TP53-RNP2-D17S1)-(MYH2-MYH1)-D17Z 1-CRYB1-(ERBA1-GCSF-NGL)-acute promyelocytic leukemia breakpoint-RNU2-HOX2-(NGFR-COLIAI-MPO)-GAA-UM PH-GHC-TK1-GALK-qter. Using chromosome-mediated gene transfer, we have also regionally localized the random probes D17S6 to D17S19 on chromosome 17.

Ascorbic acid specifically increases type I and type III procollagen messenger RNA levels in human skin fibroblast

In cultured human skin fibroblasts, ascorbic acid stimulates collagen production with no apparent change in the intracellular degradation of newly synthesized procollagen. To understand the basis for this effect, we measured the steady-state levels of type I and type III procollagen mRNAs in cells treated with ascorbic acid. A three- to fourfold increase in collagen synthesis was associated with a two- to threefold increase in the levels of mRNAs for both type I and type III procollagens. These effects of ascorbic acid are explained by a translational control linked either to procollagen gene transcription or mRNA degradation.

High recombination between two physically close human basement membrane collagen genes at the distal end of chromosome 13q

Two basement membrane collagen genes coding for the pro alpha 1 chain and pro alpha 2 chain of type IV collagen map to 13q34 and are linked with a maximum likelihood estimate of recombination of 0.028 at a logarithm of odds (lod) score of 19.98. The single-copy sequence that identifies the locus D13S3 is also closely linked to both collagen genes. Four enzymes reveal polymorphisms with COL4A1, and 10 haplotypes have been observed in Caucasoids. Within COL4A1 a nonrandom association of alleles exists only between alleles defined by Hae III and those defined by the other three enzymes. A random association of alleles of COL4A1 and COL4A2 is observed. Between the two collagen genes were detected three meiotic recombination events that contributed to the estimate of 2.8% recombination. This is higher than expected for two genes that lie within 650 kilobases of each other. The lack of linkage disequilibrium between COL4A1 and COL4A2 is in agreement with the relatively high recombination that is observed.

Chromosomal localization of the gene for a human thyroid hormone-binding protein

A cDNA for the gene that encodes for a human cellular thyroid hormone-binding protein (p55) has recently been isolated and sequenced. The sequence of p55 indicates that it is identical to the protein disulfide isomerase and the beta-subunit of prolyl 4-hydroxylase. By in situ hybridization, the gene for p55 was localized on chromosome 17 at band q25. This localization shows that the p55 gene is not linked to either erbA1 or erbA2; two other thyroid hormone-binding protein genes are located at 17q 11-21 and 3p21-pter, respectively. The localization of p55 gene will permit the evaluation of the possible effects of chromosome changes on the structure and activity of the p55 gene in chromosome syndromes or neoplasms.

Cloning and chromosomal localization of human genes encoding the three chains of type VI collagen

Type VI collagen is a heterotrimer composed of three polypeptide chains, alpha 1(VI), alpha 2(VI), and alpha 3(VI). By immunological screening of an expression cDNA library, human cDNAs specific for each chain were isolated and characterized. Major mRNA species encoding these chains have a size of 4.2 kb (alpha 1), 3.5 kb (alpha 2), and 8.5 kb (alpha 3). The cDNA clones were also used to map the genes on human chromosomes by somatic cell hybrid analysis and in situ hybridization. The alpha 1 (VI) and alpha 2(VI) collagen genes were both located on chromosome 21, in band q223. This represents a third example of a possible physical proximity of two collagen loci. The alpha 3(VI) collagen gene was localized to chromosome 2, in the region 2q37. The alpha 3(VI) collagen gene is the fifth extracellular matrix gene to be localized to 2q, as four other extracellular matrix genes--i.e., the alpha 1(III) and alpha 2(V) collagen genes, the elastin gene, and the fibronectin gene--have been previously mapped to the distal region of the long arm of chromosome 2.

The genes coding for human pro alpha 1(IV) collagen and pro alpha 2(IV) collagen are both located at the end of the long arm of chromosome 13

We have isolated and characterized a cDNA clone containing DNA sequences coding for the noncollagenous carboxy-terminal domain of human pro alpha 2(IV) collagen. Using this cDNA clone in both Southern blot analysis of DNA isolated from human-mouse somatic-cell hybrids and in situ hybridization of normal human metaphase chromosomes, we have demonstrated that the gene coding for human pro alpha 2(IV) collagen is located at 13q33----34, in the same position on chromosome 13 as the pro alpha 1(IV) collagen gene.

Partial structure of the human alpha 2(IV) collagen chain and chromosomal localization of the gene (COL4A2)

We have isolated a 2.1-kb cDNA clone from a human placental library encoding part of the alpha 2 chain of collagen IV, a major structural protein of basement membranes. The DNA sequence encodes 446 amino acids in the triple-helical domain plus the 227 amino acids of the carboxy-terminal globular domain. The latter structure is composed of two homologous subdomains and is highly conserved between the alpha 1 and alpha 2 chains. The triple-helical domain contained seven interruptions of the Gly-X-Y repeat and these interruptions were in general larger than their counterparts in the alpha 1 chain. DNA from human rodent hybrid cell lines was analyzed under conditions in which there was no cross-hybridization of the alpha 2(IV) cDNA probe with the gene for the alpha 1(IV) collagen chain. An EcoRI fragment characteristic of the alpha 2 chain had a concordance of 0.97 with chromosome 13. This result was confirmed and extended with in situ localization of the gene at 13q34. Since the alpha 1(IV) gene has previously been localized to 13q34, the two type IV collagen genes reside in the same chromosome region (13q34), possibly in a gene cluster. The presence of the genes for type IV collagen chains on chromosome 13 excludes a primary role for these genes in adult polycystic kidney disease and X-linked forms of hereditary nephritis.

Chromosomal localization of ceruloplasmin and transferrin genes in laboratory rats, mice and in man by hybridization with specific DNA probes

Fragments of the natural rat ceruloplasmin (Cp) gene and cDNA copies of rat Cp and transferring (Tf) mRNAs highly labelled by nick translation with 125I-dCTP were used as specific probes for assignment of these genes to the metaphase chromosomes of rat, mouse and man by in situ hybridization. Both Cp and Tf genes were found to be syntenic in rodents, occupying with high probability the regions 9D and 9F1-3 in mice and 7q11-13 and 7q31-34 in rats respectively. The significant increase in silver grain count over chromosome 15 in rats after hybridization with both the Cp and Tf probes suggests the presence of a related pseudogene cluster on this particular chromosome and thus favours its partial homeology to chromosome 7. The localization of silver grains in metaphase chromosome of man indicates subregional assignment of the Tf gene to 3q21. Use of the rat Cp DNA probe does not indicate synteny of the Cp and Tf genes in man and suggests the existence of a related DNA sequence in 15q11-13. The potential and limitations of the in situ hybridization technique with heterologous DNA probes for gene mapping in mammalian species are discussed.

The physical map of Mus musculus chromosome 11 reveals evolutionary relationships with different syntenic groups of genes in Homo sapiens

The physical localization of sequences homologous to three cloned genes was determined by in situ hybridization to metaphase chromosomes. Previous work had assigned the skeletal myosin heavy chain gene cluster (Myh), the functional locus for the cellular tumor antigen p53 (Trp53-1), and the cellular homologue of the viral erb-B oncogene (Erbb) to Mus musculus chromosome 11 (MMU11). Our results provide regional assignments of Myh and Trp53-1 to chromosome bands B2----C, and of Erbb to bands A1----A4. Taken together with in situ mapping of three other loci on MMU 11 (Hox-2 homeobox-containing gene cluster, the Sparc protein, and the Colla-1 collagen gene), which have been reported elsewhere, these data allowed us to construct a physical map of MMU11 and to compare it with the linkage map of this chromosome. The map positions of the homologous genes on human chromosomes suggest evolutionary relationships of distinct regions of MMU11 with six different human chromosome arms: 1p, 5q, 7p, 16p, 17p, and 17q. The delineation of conserved chromosome regions has important implications for the understanding of karyotype evolution in mammalian species and for the development of animal models of human genetic diseases.

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.

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.

Osteogenesis imperfecta type IV. Biochemical confirmation of genetic linkage to the pro alpha 2(I) gene of type I collagen

Fibroblasts from two affected members of a large pedigree in which osteogenesis imperfecta (OI) type IV is genetically linked to the pro alpha 2(I) gene of type I collagen synthesize two populations of pro alpha 2(I) chains. One population is normal; the second population appears to have a deletion of about 10 amino acid residues from the middle of the triple helical domain. The mutation in pro alpha 2(I) causes increased posttranslational modification in the amino-terminal half of some pro alpha 1(I) chains, lowers the melting temperature of type I collagen molecules that incorporate a mutant pro alpha 2(I) chain, and prevents or delays the secretion of those molecules from fibroblasts in cell culture. On the basis of this study and linkage studies in additional families, it appears that the OI type IV phenotype is often the result of heterozygosity for mutations in pro alpha 2(I) that alter the triple helical structure of type I collagen.

Cognate homeo-box loci mapped on homologous human and mouse chromosomes

The homeotic genes of Drosophila, which regulate pattern formation during larval development, contain a 180-base-pair DNA sequence termed the "homeo-box." Nucleotide sequence comparisons indicate that the homeo-box motif is highly conserved in a variety of motazoan species. As in Drosophila, homeo-box sequences of mammalian species are expressed in a temporal and tissue-specific pattern during embryogenesis. These observations suggest functional homologies between dipteran and mammalian homeo-box gene products. To identify possible relationships between homeo-box genes of mice and humans, we have compared the chromosomal location of homeo-box genes in these species. Using in situ hybridization and somatic cell genetic techniques, we have mapped the chromosome 6-specific murine Hox-1 homolog to the region p14-p21 on human chromosome 7. We have also regionally mapped the murine Hox-3 locus to 15F1-3 and its human cognate to 12q11-q21. These comparative mapping data indicate that a syntenic relationship in mice and humans is maintained for all homeo-box loci examined to date. We suggest these regions represent evolutionarily conserved genomic domains encoding homologous protein products that function in regulating patterns of mammalian development.

The single copy gene coding for human alpha 1 (IV) procollagen is located at the terminal end of the long arm of chromosome 13

Using dual-laser sorted chromosomes and spot-blot analysis, we have previously assigned genomic DNA sequences coding for human alpha 1 (IV) procollagen to chromosome 13 (Pihlajaniemi et al. 1985). By in situ hybridization to normal chromosomes and chromosomes with 13q deletions, we now report the localization of this gene to the terminal end of the long arm of chromosome 13. In addition, Southern and slot blot hybridization analysis clearly show that these genomic sequences are present only once per haploid genome.

The pro alpha 2(V) collagen gene (COL5A2) maps to 2q14----2q32, syntenic to the pro alpha 1 (III) collagen locus (COL3A1)

A recombinant probe specific for the pro alpha 2 chain of human Type V collagen has been used for the localization of the corresponding gene (COL5A2) to chromosome 2. Regional mapping by in situ hybridization and analysis of DNA from human X rodent cell lines indicated that COL5A2 is confined within the segment 2q14----2q32, thus syntenic to the pro alpha 1 (III) collagen gene (COL3A1).

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.