Regulation of the expression of genes encoding types I, II, and III collagen during chick embryonic development

COL1A2 Barcoding: Bone Species Identification via Shotgun Proteomics

Species identification of fragmentary bones remains a challenging task in archeology and forensics. A species identification method for such fragmentary bones that has recently attracted interest is the use of bone collagen proteins. Here, we describe a method similar to DNA barcoding that reads collagen protein sequences in bone and automatically determines the species by performing sequence database searches. The method is almost identical to conventional shotgun proteomics analysis of bone samples, except that the database used by the SEQUEST search engine consisted only of entries for collagen type 1 alpha 2 (COL1A2) proteins from various vertebrates. Accordingly, the COL1A2 peptides that differ in sequence among species act as species marker peptides. In SEQUEST-based shotgun proteomics, the protein entries that contain more marker peptide sequences are assigned higher scores; therefore, the highest-scoring protein entry will be the COL1A2 entry for the species from which the analyzed bone was derived. We tested our method using bone samples from 30 vertebrate species and found that all species were correctly identified. In conclusion, COL1A2 can be used as a bone protein barcode and can be read through shotgun proteomics, allowing for automatic bone species identification. Data are available via ProteomeXchange with the identifier PXD045402.

Effect of Hydrogen Oxide-Induced Oxidative Stress on Bone Formation in the Early Embryonic Development Stage of Chicken

The current study aimed to monitor the impact of H₂O₂-induced oxidative stress on avian bone formation during the early stage of embryonic development. Fertilized Cobb broiler eggs were divided into five treatment groups and micro-injected with varying concentrations of H₂O₂, i.e., control (PBS; 0 nM), 10 nM, 30 nM, 100 nM, and 300 nM, on embryonic day 3, with continued incubation thereafter. The treatment concentrations were selected based on the level of lipid peroxidation and the survival rate of embryo. Embryos were collected at 6 h, 24 h, 48 h, and 72 h post-injection. The mRNA expression levels of apoptotic markers, antioxidant enzymes, and early bone formation gene markers were measured. The results showed that the microinjection of H₂O₂ altered the expression pattern of antioxidant enzymes' mRNA during early embryogenesis and decreased the expression of COL1A2 and COL2A1 at 6 h and 24 h post-injection. Decreased expression of BMP, BGLAP, and RUNX2 was observed 48 h post-injection. Additionally, a shorter embryo length was observed in the 100 nM and 300 nM H₂O₂ treatment groups 72 h post-injection. In conclusion, H₂O₂-induced oxidative stress suppressed the expression of bone formation gene markers, with chronic effects on avian embryonic development.

Learning from regeneration research organisms: The circuitous road to scar free wound healing

The skin is the largest organ in the body and plays multiple essential roles ranging from regulating temperature, preventing infection and ultimately defining who we are physically. It is a highly dynamic organ that constantly replaces the outermost cells throughout life. However, when faced with a major injury, human skin cannot restore a significant lesion to its original functionality, instead a reparative scar is formed. In contrast to this, many other species have the unique ability to regenerate full thickness skin without formation of scar tissue. Here we review recent advances in the field that shed light on how the skin cells in regenerative species react to injury to prevent scar formation versus scar forming humans.

Structural and functional studies on the interstitial collagen genes

An understanding of the molecular mechanisms which control expression of the type I and III collagen genes may provide a rational basis for the design of more effective therapeutic approaches to fibrotic diseases. The structure of the interstitial collagen genes is reviewed and potential sites which could control their expression are examined. One approach to the study of the regulation of these genes consists in DNA-mediated gene transfection experiments and is discussed in this paper.

Late Deposition of Elastin to Vertical Microfibrillar Fibers in the Presumptive Dermis of the Chick Embryonic Tarsometatarsus

Fibrillin microfibrils are integral components of elastic fibers and serve as a scaffold for elastin deposition. However, microfibrillar fibers (MFs) are not necessarily committed to develop into so-called elastic fibers. In dermis, elastin-free oxytalan MFs originating from the dermoepidermal junction are continuous to elaunin-type MFs (with a small amount of elastin) in the deeper papillary dermis, whereas the reticular dermis contains elastic fibers, or MFs embedded largely in elastin. In this study, we have investigated temporospatial patterns of elastin deposition on the MFs in tarsometatarsal presumptive dermis. While the earliest expression of elastin was demonstrated immunohistochemically as early as embryonic day 4 (ED4) in the wall of cardiac outflow and pharyngeal arch arteries, its deposition in the tarsometatarsus was first detected at ED6 in the deeper mesenchyme and at ED13 in the subectodermal mesenchyme. In the latter tissue, MFs had been organized perpendicularly to the covering ectoderm by ED4, well before an overt accumulation of collagenous matrix. Elastin deposition was observed initially in a punctate manner at ED13 and afterward became continuous along MFs. However, a characteristic spaced array of subectodermal vertical MFs was disorganized by ED17. These findings suggest that elastin deposition in the subectodermal MFs is not deployed by continuous, orderly propagation from elastic fibers in the deeper mesenchyme but occurs de novo in multiple foci along vertical MFs. Moreover, the present chronology of elastin deposition indicates that subectodermal, elastin-free MFs function as a transient, but primary fibrous structure in the presumptive dermis before the accumulation of collagenous matrix.

Subectodermal microfibrillar bundles are organized into a distinct parallel array in the developing chick limb bud

In this study, a unique fiber system in the subectodermal mesenchyme of the chick limb bud was visualized immunohistochemically with the use of a novel monoclonal antibody termed "FB1." This antibody stained a subset of extracellular fibers in the embryonic mesenchyme. Among the fibers visualized, those running perpendicularly to the limb bud ectoderm became progressively prominent in their thickness and length, and organized into a parallel array in the subectodermal region. This fiber system was distinct from that of major collagens, fibronectin, or tenascin. A molecule immunoprecipitated with FB1 comigrated with JB3 antigen, or chicken fibrillin-2. The fibers visualized immunohistochemically by FB1 and JB3 were indistinguishable from each other, and ultrastructurally appeared to be bundles composed of tubular-like microfibrils that originated directly from the ectodermal basal lamina. They lacked the amorphous deposits that are characteristic of elastin. A similar array of subectodermal fibers was also found in the developing axilla and some truncal regions, again well before the development of a definitive dermis. These findings suggest that a parallel array of subectodermal FB1-positive fibers constitutes a precocious fiber system in the presumptive dermis prior to the substantial formation of collagenous fibers. These fibers could be developmentally linked to oxytalan fibers, which are known to be present in the papillary dermis in mature cutaneous tissue.

Developmental gene expression of procollagen III in bovine extraembryonic membranes during early pregnancy

A major secretory protein produced by bovine chorioallantoic membranes, in vitro, was previously identified as the carboxyl-propeptide of alpha-1 type III collagen. In the present study, the protein and gene expression of procollagen III by bovine chorioallantois between days 17 and 45 of pregnancy was investigated. In addition, differential usage of multiple transcription termination sites by chorioallantois was examined. Two-dimensional PAGE of proteins synthesized and released by whole conceptuses or isolated chorioallantoic membranes into culture medium demonstrated that the C-terminal of procollagen III was not detectable before day 21 of pregnancy and concentrations increased thereafter. Developmental gene expression was determined by Northern blot analysis using a probe (A) that preceded all five polyadenylation sites of the previously sequenced clone 9.22. Procollagen III mRNA expression was undetectable at day 17, low on day 20, and increased through day 36. Two major transcripts of 5.9 and 4.9 kb were identified, the latter of which was expressed more prominently. A second probe (B), which terminated between poly-A sites 2 and 3, was designed to identify transcripts that terminated at poly-A site 1 or 2. This probe bound to the 5.9-kb mRNA only. Two additional procollagen III cDNA clones were isolated from our bovine conceptus cDNA library and sequenced. One, designated 9.29, terminated at poly-A site 5. The other, designated 11.7, terminated at poly-A site 2, indicating that the bovine conceptus uses these stop sites in procollagen III transcription. Results from this study demonstrate that procollagen III gene and protein expression coincide with the development of the allantois, which progressively fuses with the chorion forming the chorioallantois placenta. In addition, multiple termination sites are used in procollagen III transcription.

Expression of the alpha-5(IV) collagen chain in the fetal human small intestine

BACKGROUND/AIMS

The basement membrane type IV collagen is a family composed of at least five genetically distinct but structurally similar polypeptide chains, alpha 1-alpha 5. The alpha 1(IV) and alpha 2(IV) chains are ubiquitous components of basement membranes, whereas the alpha 3(IV), alpha 4(IV), and alpha 5(IV) chains have a restricted tissue distribution. The aim of this study was to analyze the presence of these minor type IV collagen chains in the small intestinal mucosa.

METHODS

The expression of type IV collagen chains in the developing and adult human small intestine was determined by indirect immunofluorescence with monoclonal and polyclonal antibodies. Western blotting and Northern hybridization analysis were also used to additionally investigate the expression of the alpha 1(IV) and alpha 5(IV) chains.

RESULTS

The alpha 3-alpha 5(IV) chains were absent from the adult epithelium, but, surprisingly, the alpha 5(IV) chain was consistently detected in the fetal mucosa. Its expression was confirmed by Western blotting, complementary DNA polymerase chain-reaction amplification, and Northern hybridization analysis.

CONCLUSIONS

The alpha 5(IV) chain of collagen is expressed in the fetal but not adult human intestinal epithelium. Its position at the basolateral domain of epithelial cells suggests a potential role for this molecule during development.

Presence of the factor that inhibits collagen synthesis and stimulates cell proliferation in developing embryonic chick skin extracts

The effects were studied of the extracts prepared from 10- and 18-day developing chick skins on collagen synthesis and proliferation of the monolayered fibroblasts established from 10-day skin. Cell proliferation was stimulated by both 10- and 18-day skin extracts at the concentration of 3.5 micrograms/ml. Collagen synthesis was suppressed by the treatment of extracts prepared from both 10- and 18-day skins at the concentration of 3.5 micrograms/ml, to a greater extent in 18-day extract. The results indicate that skin extracts possess factors exhibiting both a stimulating effect on cell proliferation and an inhibitory effect on collagen synthesis.

Comparison on collagen gene expression in the developing chick embryo tendon and heart. Tissue and development time-dependent action of dexamethasone

Glucocorticoids modulate various cellular functions such as proliferation, energy metabolism and the synthesis of proteins. In the present study, the response of collagen genes to dexamethasone in different stages of chick embryo development was studied in tendon and heart using Northern blot analysis and specific cDNA probes. The changes in collagen gene expression were compared to alterations in two reference mRNAs: actin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The levels of specific mRNAs measured per ribosomal RNA in tendon and heart varied markedly during normal development. In tendon the relative levels of alpha 1(I), alpha 2(I) and alpha 1(III) collagen mRNAs were highest between days 14-16 when also the synthesis of matrix proteins is most active. In heart the levels of these mRNAs peaked at day 12. In addition, qualitative differences were observed in the expression of actin genes between tendon and heart. Dexamethasone in high dose decreased collagen mRNA levels in tendons, while in heart a stimulatory effect was noted. Dexamethasone also decreased GAPDH mRNA levels in tendons. The alterations in gene expression after dexamethasone treatment in tendon and heart did not correlate with the level of specific glucocorticoid receptors, which varied markedly during the development of chick embryos. The cDNA for pro alpha 1(I) collagen hybridized to two transcripts corresponding to 6.2 and 5.1 kb in tendon and heart. During normal development of chick embryos the ratio of 6.2/5.1 kb mRNAs decreased markedly in heart, but no such change was observed in tendons. Dexamethasone, however, decreased the ratio of 6.2/5.1 kb transcripts in tendons. There was a significant correlation between the ratio 6.2/5.1 kb transcripts and total alpha 1(I) mRNA both in tendon and heart, suggesting that the 6.2 kb transcript may be associated with the rate of synthesis of type I collagen.

Optimal heat-induced expression of the Drosophila hsp26 gene requires a promoter sequence containing (CT)n.(GA)n repeats

We report here the analysis of the sequence requirements for the heat-induced expression of the Drosophila melanogaster hsp26 gene using germline transformation. Heat-induced expression is augmented fivefold by a homopurine/homopyrimidine region from -85 to -134 that is devoid of heat-shock elements but contains numerous (dC-dT).(dG-dA) repeats. Sequences within this interval have been shown to assume a nuclease S1-hypersensitive structure in vitro. In this paper, we extend those in vitro observations, demonstrating that the S1-hypersensitive structure is triple-helical H-DNA formed by a symmetric (dC-dT).(dG-dA) sequence. Thus, the sequences that form H-DNA in vitro are also required in vivo for optimal hsp26 transcription. However, mutational analysis and diethylpyrocarbonate modification experiments in isolated nuclei suggest that the (dC-dT).(dG-dA) sequence does not form H-DNA in vivo and argue against a role for H-DNA in the heat-induced expression of hsp26.

Expression of cartilage-matrix genes and localization of their translation products in the embryonic chick eye

The presence of cartilage-matrix molecules in the embryonic chick eye was shown by means of measuring RNA expression and immunostaining studies. The molecules examined were proteoglycan core protein (PG-core), link protein (LP), cartilage-matrix protein (CMP) and type II collagen. The genes encoding these proteins are expressed in 8- to 11-day embryonic chick eyes at constant steady-state levels. Immunopositive stained tissues include sclera, choroid, cornea, lens capsule (PG-core, LP, CMP), lens epithelium, lens fibers (LP, CMP) and the membranes in the retina (LP). In addition, data from comparative studies employing the eyes from the proteoglycan core-protein-deficient mutant, nanomelia, indicate that levels of mRNA for core protein are almost absent and that CMP is reduced in the above-mentioned tissues.

Isolation of cDNA clones corresponding to the Mr = 150,000 subunit of chick type VI collagen

Type VI collagen is a disulfide-bonded protein with an unusual structure in that the molecule contains three short triple-helical domains and very extended non-collagenous regions. The molecule is a heterotrimer composed in the chick of two polypeptides of similar apparent size in SDS-PAGE (Mr = 140- and 150,000) but different structure, and a third component that is much larger (Mr = 260,000) than the other two chains. We report here on the isolation of several overlapping cDNA clones from a chicken aorta mRNA expression library in the plasmid vector pEX1. Antibodies affinity purified onto the fusion proteins recognized the chick type VI collagen Mr = 150,000 subunit. Northern blots using the cDNA inserts from the above clones revealed a single RNA species of about 4,600 nucleotides sufficient to code for a protein with the size of the Mr = 150,000 subunit.

Collagen gene expression in keloids: analysis of collagen metabolism and type I, III, IV, and V procollagen mRNAs in keloid tissue and keloid fibroblast cultures

Regulation of collagen gene expression was studied in keloids and fibroblast cultures established from keloid biopsies from 9 patients. The collagen concentration in keloid tissue was not different from that in normal skin. The activities of 2 enzymes catalyzing intracellular collagen biosynthesis, prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyltransferase (GGT) were significantly elevated in the keloids, the mean increase in the former enzyme being 5-fold and in the latter 3-fold with respect to the controls. The mean procollagen production rate in the keloid fibroblasts was at the control level, with only 1 keloid cell line showing a procollagen synthesis rate higher than the mean value + 2 SD of the controls. The mean PH and GGT activities of the keloid fibroblasts were not elevated, but PH activity in 2 cell lines and GGT activity in 1 cell line were higher than the mean + 2 SD for the controls. Cellular type I, III, IV, and V procollagen mRNAs were measured by slot blot hybridization using specific human cDNA clones for the various collagen types. The amounts of type I, III, and V procollagen mRNAs corresponded to the ratios in which these collagen types are produced by fibroblasts. No synthesis of type IV procollagen mRNA by keloid fibroblasts was observed. The total amount of type I and III procollagen mRNAs correlated significantly (p less than 0.01) with the procollagen synthesis rate measured after radioactive labeling of the cells in the keloid and control fibroblasts, indicating that collagen production in these cells is mainly controlled by regulating the final steady state levels of collagen mRNA. The results suggest that fibroblasts isolated from keloids often synthesize normal amounts of collagen.

Regulation of collagen gene expression in cutaneous diseases with dermal fibrosis: evidence for pretranslational control

Dermal fibrosis, characterized by collagen accumulation, is the hallmark of several cutaneous diseases. To examine the mechanisms of collagen deposition in fibrotic skin diseases, fibroblast cultures were established from the skin of patients with progressive systemic sclerosis, morphea, scleredema, familial cutaneous collagenoma, connective tissue nevi of the collagen type, or keloids; these patients served as prototypes of fibrotic skin diseases with varying clinical features and potentially different etiologic factors. Collagen production was assayed by the synthesis of [3H]hydroxyproline, and types I and III procollagen messenger RNA (mRNA) levels were determined by dot blot hybridizations using human type I and type III procollagen-specific cDNA probes. The collagen production in fibroblast cultures from the fibrotic diseases was increased up to 6-fold over the controls, and a relatively good correlation between the collagen production and type I collagen mRNA levels was noted. The type I/III procollagen mRNA ratio in control fibroblast cultures was 5.9 +/- 1.6 (mean +/- SD). The corresponding ratio in keloid cell culture was markedly increased, while slightly decreased values were noted in the case of morphea and familial cutaneous collagenoma; the values in other cultures were within the normal range. The results suggest that procollagen production in fibroblast cultures derived from fibrotic skin diseases reflects elevated levels of the corresponding procollagen mRNA. The increased mRNA abundance, suggesting pretranslational control, may result from enhanced transcriptional activity of the corresponding gene or alternatively reflects increased stability of the mRNA molecule.

Procollagen gene expression by scleroderma fibroblasts in culture. Inhibition of collagen production and reduction of pro alpha 1(I) and pro alpha 1(III) collagen messenger RNA steady-state levels by retinoids

Recent studies have demonstrated that retinoids (synthetic vitamin A analogs) can modulate connective tissue metabolism in human skin fibroblast cultures. In this study, we examined the effects of 3 retinoids, all-trans-retinoic acid (RA), 13-cis-RA, and an aromatic retinoid, RO-10-9359, on collagen gene expression in scleroderma fibroblast cultures and matched control fibroblast cultures. The results indicated that all-trans-RA and 13-cis-RA significantly reduced procollagen production both in control and scleroderma fibroblast cultures in a dose-dependent manner. The reduction in procollagen production was paralleled by a similar decrease in steady-state levels of type I and type III procollagen messenger RNAs, which suggests that there is coordinate inhibition on the transcriptional level. In contrast, RO-10-9359 elicited only limited effects on collagen production, and such effects were variable. The results suggest that further development of retinoids might provide an effective means to counteract tissue deposition of collagen in scleroderma and other fibrotic diseases.

Expression of extracellular matrix genes in relation to myogenesis and neoplastic transformation

Fibronectin and alpha 1(I) and alpha 2(I) collagen proteins and RNAs are highly expressed during the growth phase of the non-transformed L6 alpha 1 rat myoblasts. When L6 alpha 1 cells from myotubes following transfer to low serum medium, the levels of fibronectin RNA decrease 8-fold, those of both alpha 2(I) transcripts decrease only 2-fold, while those of both alpha 1(I) transcripts remain stable. The L6 alpha 1 cell-derived non-differentiable low-malignant M4 cell and high-malignant RMS4 cell display only one size of alpha 1(I) and alpha 2(I) transcripts. Compared with L6 alpha 1 myoblasts, the levels of fibronectin and alpha 1(I) RNAs are reduced by factors of 4-5 and 9-10 respectively in both M4 and RMS4 and those of alpha 2(I) RNAs by factors of 10-11 and 20-22 in M4 and RMS4, respectively. Transcription rates are similarly decreased for fibronectin RNA, but are decreased less for collagen RNAs.

Sequence-specific DNA-binding proteins which interact with (G + C)-rich sequences flanking the chicken c-myc gene

The interaction of nuclear sequence-specific DNA-binding proteins from definitive chicken erythrocytes, thymus and proliferating transformed erythroid precursor (HD3) cells with the 700-base-pair (700-bp) DNA 5'-flanking region of the chicken c-myc gene was investigated by in vitro footprint analysis. The major HD3 protein-binding activity binds to a site (site V) 200 bp upstream from the 'cap' site but, after further fractionation, a second distinct binding activity is detected to a site (site VIII) which contains both the 'CAAT' and 'SP1-binding' consensus sequences. Protein from thymus and erythrocyte cells which express c-myc at lower levels, bind to seven and eight sites respectively. In common with HD3 cell protein, they both bind to site VIII and, although binding to the sequence at site V is also detected, the footprint protection pattern is sufficiently different (site V') to suggest the involvement of different proteins in terminally differentiated and proliferating cells. The DNA-binding activities were partially fractionated by high-performance liquid chromatography gel filtration and include an erythrocyte-specific protein which binds to a c-myc gene poly(dG) homopolymer sequence similar to that found upstream of the chicken beta A-globin gene.

Demonstration of elevated type I and type III procollagen mRNA levels in cutaneous wounds treated with helium-neon laser. Proposed mechanism for enhanced wound healing

To assess laser modulation of wound healing, full-thickness cutaneous wounds were produced in the backs of pigs, and subjected to treatment with helium-neon laser. For comparison, some wounds were treated with non-laser energy source (a tungsten light) or left untreated as controls. Type I and type III procollagen mRNA levels were determined in the wounds by molecular hybridization with cDNA probes. The results indicated that type I and type III mRNA levels were markedly increased at days 17 and 28 of the healing in wounds treated with He-Ne laser, when compared to control or tungsten light-treated wounds. The results suggest that helium-neon laser stimulates wound healing by enhancing procollagen gene expression. These observations may have relevance to previous clinical studies suggesting that helium-neon laser stimulates wound healing.

Progressive nodular fibrosis of the skin: altered procollagen and collagenase expression by cultured fibroblasts

A 33-year-old man presented with a spontaneous progressive cutaneous tumor-like fibrosis involving the right leg and buttock. Histologically the deep dermis was composed of numerous fibroblasts and dense bands of collagen, suggesting that the lesion might be related to an abnormality in collagen metabolism. Fibroblast cultures were established from the affected and normal-appearing skin. The growth rate of the lesional cells was essentially equal to that of control cells. The synthesis of procollagen was approximately 3.5-fold increased in the cells derived from the nodules when compared with control fibroblasts (p less than 0.001). The increase in procollagen synthesis was reflected by an approximate 6-fold increase in both type I and type III procollagen mRNA abundance in the lesional fibroblasts (p less than 0.001), thus suggesting an aberration in the pretranslational level of procollagen gene expression. In contrast, the synthesis of collagenase, the enzyme required for the initiation of collagen degradation, was decreased to approximately 25% of control values (p less than 0.0025), although the enzyme was catalytically normal. The data indicate that these cells are characterized by an increased synthesis of procollagen and decreased synthesis of collagenase, 2 phenotypic characteristics that could account pathophysiologically for the lesions. The unusual reciprocal nature of these biochemical parameters in 2 proteins important in connective tissue homeostasis suggests that this progressive tumor-like condition may have resulted from the expansion of a clonal population of cells.

The effects of chronic ozone exposure on pulmonary collagen content and collagen synthesis in rats

Male rats were exposed to 0.125, 0.25 or 0.5 ppm of ozone or clean air for up to 1 year. During this exposure period there was little evidence for collagen accumulation in the lungs. However, the rate of incorporation of tritiated proline into both lung collagen and total lung protein was accelerated. These data suggest that exposure to ozone under these conditions results in an increase in the turnover of collagen as well as other lung proteins.

Biochemical composition of the connective tissue in keloids and analysis of collagen metabolism in keloid fibroblast cultures

Keloids are histologically characterized by an abundance of the extracellular matrix of connective tissue. In the present study, we examined the connective tissue composition of keloids, and analyzed the details of collagen metabolism utilizing fibroblast cultures established from keloid tissue. Quantitative connective tissue analyses indicated that collagen was the predominant extracellular matrix component in keloids. The ratio of genetically distinct collagens type I/III was significantly increased, as compared to normal human skin. Collagen biosynthesis was measured in fibroblast cultures by the formation of radioactive hydroxyproline: 5 of 9 keloid cell cultures studied demonstrated increased procollagen production in comparison to age-, sex-, and passage-matched control skin fibroblast lines, while the remaining 4 cell lines were within the control range. Keloid fibroblast cultures which were high collagen producers also demonstrated elevated prolyl hydroxylase activity. The mechanisms of increased procollagen production in fibroblast cultures were first examined by assaying the abundance of type I procollagen-specific mRNA utilizing dot blot hybridizations with a pro alpha 2(I)-chain-specific cDNA. The type I procollagen mRNA levels were significantly increased in 4 keloid fibroblast lines, and a good correlation between the mRNA levels and the rate of procollagen production in the same cultures was noted. These observations suggest regulation of the collagen gene expression on the transcriptional level. The catabolic pathway of collagen metabolism in fibroblast cultures was examined by determining the degradation of newly synthesized procollagen polypeptides through assay of radioactive hydroxyproline in small-molecular-weight peptide fragments. In 3 keloid cell cultures, the degradation of newly synthesized collagen polypeptides was below the range of normal controls. These findings suggest that a reduced degradation of newly synthesized polypeptides might contribute to the accumulation of procollagen in some keloid fibroblast cultures. The results of this study suggest two possible mechanisms for deposition of collagen in keloid lesions in vivo: first, the growth of the lesions may result from a localized loss of control of the extracellular matrix production by fibroblasts; secondly, reduced degradation of the newly synthesized procollagen polypeptides may contribute to collagen deposition in some keloids.

Quantitation of type II procollagen mRNA levels during chick limb cartilage differentiation

A single-stranded DNA probe complementary to chicken type II procollagen mRNA has been used to quantitate levels of that mRNA present in chicken limb mesenchyme during cartilage differentiation. Excess labeled probe prepared from a cDNA template cloned in M13mp9 was hybridized to completion to increasing amounts of total RNA and assayed by protection from S1 nuclease digestion. Estimates of the absolute levels of type II procollagen RNA were determined using the M13mp9 template containing the coding strand as a standard. RNA complementary to the probe increased from 20 copies per diploid genome in stage 24 limb to approximately 2000 copies per diploid genome in stage 24 limb mesenchyme which had differentiated to cartilage in culture. Similar levels were found in cartilage from stage 31 limb. Sternal cartilage from 17-day embryos contained approximately 10,000 copies per diploid genome suggesting that the level of expression of this gene is different in limb growth cartilage compared with sternal cartilage. Low but detectable levels of RNA complementary to the probe were observed in limb at stages 20-24. Since a large fraction of the type II procollagen RNA in these early limbs is associated with polysomes, the type II procollagen gene appears to be expressed at a low level prior to phenotypic differentiation and prior to the accumulation of immunologically detectable levels of type II collagen.

Peptide-maps of procollagen (I) from corneas and tendons of 17-day-old chick embryos

Corneas and tendons dissected from 17-day-old chick embryos were labeled with [35S]methionine in the presence of 0.3 mM alpha,alpha'-dipyridyl. The unhydroxylated, 35S-labeled pro alpha chains and alpha chains were isolated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The pro alpha and alpha chains were then subjected to peptide-map analysis by proteolytic digestion with trypsin and alpha-chymotrypsin, papain or proteinase K. The peptide-maps derived from cornea and tendon pro alpha 1(I) chains are identical. Similar results were obtained from cornea and tendon alpha 1(I) chains. There were differences in the peptide maps derived from cornea and tendon pro alpha 2(I) chains. However, no difference was observed in alpha 2(I) chains. These results suggest that cornea and tendon pro alpha 1(I) chains are probably identical in primary structures, whereas the cornea pro alpha 2(I) chain may be different from the tendon pro alpha 2(I) chain within pepsin sensitive regions of the procollagen molecule. The reason for difference in the peptide-maps of pro alpha 2(I) chains remain unknown. One of the possible explanations is the variation of posttranslational modification within the propeptides of the pro alpha 2(I) chain. However, this hypothesis needs to be further investigated. Nevertheless, the finding that the peptide-maps of alpha 2(I) chains from tendons and corneas are identical fail to support the two genes hypothesis for pro alpha 2(I) chains.

Retrovirus-induced lethal mutation in collagen I gene of mice is associated with an altered chromatin structure

The chromatin structure of the collagen alpha 1(I) gene, which has been mutated by retrovirus insertion in Mov13 mice, was compared with that of the wildtype allele. Limited digestions with DNAase I revealed the presence of two hypersensitive sites in all normal cells analyzed, while a third site at 100 to 200 bp 5' of the transcription start was detected only in cells synthesizing collagen alpha 1(I) mRNA. This transcription-associated site was not present in chromatin of the mutant allele, while the two other hypersensitive sites, one of which is located close to the provirus, were not changed by the virus integration. Our results suggest that the virus insertion in Mov13 mice may prevent the developmentally regulated appearance of a transcription-associated hypersensitive site, thereby interfering with proper activation of the gene during embryonic development.

Amplification and enhanced expression of the epidermal growth factor receptor gene in A431 human carcinoma cells

The sequence of the human epidermal growth factor (EGF) receptor shows great homology with the avian erythroblastosis virus v-erb B oncogene, raising the possibility that the receptor gene is identical to the c-erb B protooncogene. Human A431 epidermoid carcinoma cells, which have an unusually high number of EGF receptors, were examined to determine whether elevated EGF receptor levels correlate with gene amplification. Southern blots of genomic DNA's from A431 and other human cell lines were probed with either a v-erb B gene fragment or a human EGF receptor complementary DNA clone (pE7), previously isolated from an A431 complementary DNA library. When either probe was used to analyze Eco RI- or Hind III-generated DNA fragments, EGF receptor DNA sequences were amplified about 30-fold in A431. Differences in the banding pattern of A431 DNA fragments relative to normal fibroblast DNA indicate the occurrence of a rearrangement in the region of the receptor gene. Furthermore, A431 cells contain a characteristic, prominent 2.9-kilobase RNA. These results are consistent with the hypothesis that, in A431 cells, gene amplification, possibly associated with a translocation event, may result in the overproduction of EGF receptor protein or the appearance of the transformed phenotype (or both).