Ehlers-Danlos syndrome type IV: a single base substitution of the last nucleotide of exon 34 in COL3A1 leads to exon skipping

Lumenato protects normal human dermal fibroblasts from neutrophil-induced collagen-3 damage in co-cultures

Collagen is the major structural protein in the extracellular matrix of skin produced by fibroblasts. UV exposure results in infiltration of neutrophils within the epidermis and dermis, inducing collagen damage and contributing to the process of photo-aging. Collagen-3 is an integral structural component with collagen-1, and is an important regulator of collagen-1 fibrillogenesis. Addition of neutrophils activated with TNFα to normal human dermal fibroblast cultures, but not their supernatant, caused significant collagen-3 damage. To study whether Lumenato can protect from collagen-3 damage, it was added to co-cultures of Normal human dermal fibroblasts and neutrophils activated with TNFα. Lumenato prevented collagen-3 damage induced by activated neutrophils in a dose-dependent manner in the co-cultures. Lumenato also induced a low rate of collagen-3 synthesis in a dose-dependent manner detected by pro-collagen-3 secretion, but did not affect fibroblast cell number. Although Lumenato inhibited MMP-8, MMP-9, and elastase secreted from neutrophils, its main effect was in inhibiting both NADPH oxidase-producing superoxides and MPO activity-producing halides in a dose-dependent manner that correlated with protection from collagen-3 damage. In conclusion, the results suggest that Lumenato induces low levels of collagen-3 that may contribute for skin health and is very effective in defending the co-cultures from collagen-3 damage by inhibiting free radicals secreted from neutrophils, thus, indicating Lumenato's possible potential for skin protection.

Solubilized eggshell membrane supplies a type III collagen-rich elastic dermal papilla

Signs of aging in facial skin correlate with lifespan and chronic disease; however, the health of aging skin has not been extensively studied. In healthy young skin, the dermis forms a type III collagen-rich dermal papilla, where capillary vessels supply oxygen and nutrients to basal epidermal cells. Chicken eggshell membranes (ESMs) have been used as traditional medicines to promote skin wound healing in Asian countries for many years. Previously, we designed an experimental system in which human dermal fibroblasts (HDFs) were cultured on a dish with a solubilized ESM (S-ESM) bound to an artificial phosphorylcholine polymer; we found that genes that promoted the health of the papillary dermis, such as those encoding type III collagen, were induced in the S-ESM environment. The present study found that a gel with a ratio of 20% type III/80% type I collagen, similar to that of the baby skin, resulted in a higher elasticity than 100% type I collagen (p < 0.05) and that HDFs in the gel showed high mitochondrial activity. Thus, we decided to perform further evaluations to identify the effects of S-ESM on gene expression in the skin of hairless mice and found a significant increase of type III collagen in S-ESM. Picrosirius Red staining showed that type III collagen significantly increased in the papillary dermis after S-ESM treatment. Moreover, S-ESM application significantly improved human arm elasticity and reduced facial wrinkles. ESMs may have applications in extending lifespan by reducing the loss of tissue elasticity through the increase of type III collagen.

GPR56 and the developing cerebral cortex: cells, matrix, and neuronal migration

GPR56, a member of the adhesion G protein-coupled receptor (GPCR) family, is integral to the development of the cortex, as mutations in GPR56 cause bilateral frontoparietal polymicrogyria (BFPP). BFPP is a cobblestone-like cortical malformation, characterized by overmigrating neurons and the formation of neuronal ectopias on the surface of the brain. Since its original cloning a decade ago, GPR56 has emerged from an orphaned and uncharacterized protein to an increasingly well-understood receptor, both in terms of its signaling and function. Collagen III is the ligand of GPR56 in the developing brain. Upon binding to collagen III, GPR56 activates RhoA via coupling to Gα(12/13). This pathway appears to be particularly critical in the preplate neurons, which are the earliest born neurons in the cortex, as the expression pattern of GPR56 in these neurons mimics the anterior to posterior gradient of malformation associated with loss of GPR56 in both humans and mice. Further characterizing the role of GPR56 in the preplate will shed light on the mechanism of cortical development and patterning.

Loss of Col3a1, the gene for Ehlers-Danlos syndrome type IV, results in neocortical dyslamination

It has recently been discovered that Collagen III, the encoded protein of the type IV Ehlers-Danlos Syndrome (EDS) gene, is one of the major constituents of the pial basement membrane (BM) and serves as the ligand for GPR56. Mutations in GPR56 cause a severe human brain malformation called bilateral frontoparietal polymicrogyria, in which neurons transmigrate through the BM causing severe mental retardation and frequent seizures. To further characterize the brain phenotype of Col3a1 knockout mice, we performed a detailed histological analysis. We observed a cobblestone-like cortical malformation, with BM breakdown and marginal zone heterotopias in Col3a1⁻/⁻ mouse brains. Surprisingly, the pial BM appeared intact at early stages of development but starting as early as embryonic day (E) 11.5, prominent BM defects were observed and accompanied by neuronal overmigration. Although collagen III is expressed in meningeal fibroblasts (MFs), Col3a1⁻/⁻ MFs present no obvious defects. Furthermore, the expression and posttranslational modification of α-dystroglycan was undisturbed in Col3a1⁻/⁻ mice. Based on the previous finding that mutations in COL3A1 cause type IV EDS, our study indicates a possible common pathological pathway linking connective tissue diseases and brain malformations.

G protein-coupled receptor 56 and collagen III, a receptor-ligand pair, regulates cortical development and lamination

GPR56, an orphan G protein-coupled receptor (GPCR) from the family of adhesion GPCRs, plays an indispensable role in cortical development and lamination. Mutations in the GPR56 gene cause a malformed cerebral cortex in both humans and mice that resembles cobblestone lissencephaly, which is characterized by overmigration of neurons beyond the pial basement membrane. However, the molecular mechanisms through which GPR56 regulates cortical development remain elusive due to the unknown status of its ligand. Here we identify collagen, type III, alpha-1 (gene symbol Col3a1) as the ligand of GPR56 through an in vitro biotinylation/proteomics approach. Further studies demonstrated that Col3a1 null mutant mice exhibit overmigration of neurons beyond the pial basement membrane and a cobblestone-like cortical malformation similar to the phenotype seen in Gpr56 null mutant mice. Functional studies suggest that the interaction of collagen III with its receptor GPR56 inhibits neural migration in vitro. As for intracellular signaling, GPR56 couples to the Gα(12/13) family of G proteins and activates RhoA pathway upon ligand binding. Thus, collagen III regulates the proper lamination of the cerebral cortex by acting as the major ligand of GPR56 in the developing brain.

Hydrolyzed eggshell membrane immobilized on phosphorylcholine polymer supplies extracellular matrix environment for human dermal fibroblasts

We have found that a water-soluble alkaline-digested form of eggshell membrane (ASESM) can provide an extracellular matrix (ECM) environment for human dermal fibroblast cells (HDF) in vitro. Avian eggshell membrane (ESM) has a fibrous-meshwork structure and has long been utilized as a Chinese medicine for recovery from burn injuries and wounds in Asian countries. Therefore, ESM is expected to provide an excellent natural material for biomedical use. However, such applications have been hampered by the insolubility of ESM proteins. We have used a recently developed artificial cell membrane biointerface, 2-methacryloyloxyethyl phosphorylcholine polymer (PMBN) to immobilize ASESM proteins. The surface shows a fibrous structure under the atomic force microscope, and adhesion of HDF to ASESM is ASESM-dose-dependent. Quantitative mRNA analysis has revealed that the expression of type III collagen, matrix metalloproteinase-2, and decorin mRNAs is more than two-fold higher when HDF come into contact with a lower dose ASESM proteins immobilized on PMBN surface. A particle-exclusion assay with fixed erythrocytes has visualized secreted water-binding molecules around the cells. Thus, HDF seems to possess an ECM environment on the newly designed PMBN-ASESM surface, and future applications of the ASESM-PMBN system for biomedical use should be of great interest.

α-MSH inhibits TNF-α-induced maturation of human dendritic cells in vitro through the up-regulation of ANXA1

α-Melanocyte-stimulating hormone (α-MSH), an anti-inflammatory and immunomodulatory neuropeptide, has been shown to be effective in the experimental treatment of autoimmune diseases and allograft rejection. However, its regulatory mechanism is still unclear. Mature dendritic cells (DCs) are pivotal initiators of immune response and inflammation. We hypothesized that the regulatory role of α-MSH in DC maturation would contribute to the effects of α-MSH in immune-response-mediated disease models. It was found that α-MSH inhibited tumor necrosis factor-alpha (TNF-α)-induced maturation of human peripheral-monocyte-derived DCs (MoDCs), both phenotypically and functionally. This occurred through the down-regulation of the expression of co-stimulatory molecules CD83 and CD86, the production of IL-12, the promotion of IL-10 secretion, and the MoDC phagocytic activity, suggesting that the inhibition of DC maturation by α-MSH could contribute to the anti-inflammatory effect of this neuropeptide. Furthermore, increased expression of annexin A1 (ANXA1) was found to be responsible for the α-MSH inhibiting effect on TNF-α-induced MoDC maturation, which could be abolished by the treatment of MoDCs with specific, small interfering RNAs targeting ANXA1 (ANXA1-siRNA), suggesting that α-MSH-induced ANXA1 mediates the inhibition. Therefore, α-MSH inhibits TNF-α-induced maturation of human DCs through α-MSH-up-regulated ANXA1, suggesting that inhibition of the maturation of DCs by α-MSH could mediate the anti-inflammatory effect of the neuropeptide. Furthermore, ANXA1 could be identified as a new therapeutic drug target based on the role of DCs in immune-mediated inflammatory diseases.

Haploinsufficiency of the murine Col3a1 locus causes aortic dissection: a novel model of the vascular type of Ehlers-Danlos syndrome

Aims

The vascular type of Ehlers–Danlos syndrome (EDS IV) is an autosomal-dominant disorder characterized by thin translucent skin and extensive bruising. Patients with EDS IV have reduced life expectancy (median 45–50 years) due to spontaneous rupture of arteries (particularly large arteries) or bowel. EDS IV results from mutation of the COL3A1 gene, which encodes the pro-α₁ chains of type III collagen that is secreted into the extracellular matrix, e.g. by smooth muscle cells. A mouse model of EDS IV produced by targeted ablation of Col3a1 has been of limited use as only 10% of homozygous animals survive to adulthood, whereas heterozygous animals do not die from arterial rupture. We report a novel, exploitable model of EDS IV in a spontaneously generated mouse line.

Methods and results

Mice were identified by predisposition to sudden, unexpected death from dissection of the thoracic aorta. Aortic dissection inheritance was autosomal-dominant, presented at an early age (median, 6 weeks) with incomplete penetrance, and had a similar sex ratio bias as EDS IV (2:1, male:female). Molecular genetic analysis demonstrated that the causal mutation is a spontaneous 185 kb deletion, including the promoter region and exons 1–39, of the Col3a1 gene. As in EDS IV, aortic dissection was not associated with elevated blood pressure, aneurysm formation, or infection, but may result from aberrant collagen fibrillogenesis within the aortic wall.

Conclusion

This novel, exploitable mouse line that faithfully models the vascular aspects of human EDS IV provides an important new tool for advancing understanding of EDS IV and of aortic dissection in general.

Terminal osseous dysplasia is caused by a single recurrent mutation in the FLNA gene

Terminal osseous dysplasia (TOD) is an X-linked dominant male-lethal disease characterized by skeletal dysplasia of the limbs, pigmentary defects of the skin, and recurrent digital fibroma with onset in female infancy. After performing X-exome capture and sequencing, we identified a mutation at the last nucleotide of exon 31 of the FLNA gene as the most likely cause of the disease. The variant c.5217G>A was found in six unrelated cases (three families and three sporadic cases) and was not found in 400 control X chromosomes, pilot data from the 1000 Genomes Project, or the FLNA gene variant database. In the families, the variant segregated with the disease, and it was transmitted four times from a mildly affected mother to a more seriously affected daughter. We show that, because of nonrandom X chromosome inactivation, the mutant allele was not expressed in patient fibroblasts. RNA expression of the mutant allele was detected only in cultured fibroma cells obtained from 15-year-old surgically removed material. The variant activates a cryptic splice site, removing the last 48 nucleotides from exon 31. At the protein level, this results in a loss of 16 amino acids (p.Val1724_Thr1739del), predicted to remove a sequence at the surface of filamin repeat 15. Our data show that TOD is caused by this single recurrent mutation in the FLNA gene.

Characterization of gels composed of blends of collagen I, collagen III, and chondroitin sulfate

Type I collagen is explored heavily for use in biomaterials, but the role of other extracellular matrix components in regulating collagen organization is gaining attention. We show that as the ratio of type III to type I collagen increases, fibril diameter decreases. A mixture of the two collagen types results in a more open structural network, corresponding to a more compliant material, as compared to a material composed of only one collagen type. Glycosaminoglycans also affect collagen organization and tissue properties. We show that chondroitin sulfate decreases the collagen fibril diameter. Additionally, chondroitin sulfate (CS) increases the void space of a collagen I or collagen III gel, resulting in a more compliant material, but the interactions between types I and III collagen negate the effects of CS. The simple combination of these components results in materials with unique structural, mechanical, and biological cues that can be useful in tailoring biomaterials for tissue engineering.

Comprehensive cDNA study and quantitative transcript analysis of mutantOPA1transcripts containing premature termination codons

Autosomal dominant optic atrophy (adOA) is most commonly caused by mutations in the OPA1 gene. There is a considerable allelic heterogeneity among adOA-associated OPA1 mutations, however these mutations have mostly been identified and studied only at the genomic DNA level. Here we report the identification of 22 novel OPA1 mutations and their analysis at the cDNA level along with 15 already known OPA1 mutations. We found that 18 of these mutations cause splice defects that involve either skipping of the adjacent exon or the activation of a cryptic splice site. We also observed a reduced level of the mutant transcript in several adOA subjects. Allele-specific quantification of the transcript steady-state level was performed for 13 different OPA1 mutations applying pyrosequencing to a RT-PCR amplified cSNP (c.2109C>T) in OPA1. Using this new assay we could demonstrate that the majority of OPA1 mutations that lead to a premature termination codon (PTC) undergo nonsense-mediated mRNA decay (NMD). Mutant transcript levels were reduced between 1.25- and 2.5-fold and varied between PTC containing mutations, and between subjects. Our results emphasize the value of cDNA analysis in the characterization of OPA1 mutations and further strengthen the model of haploinsufficiency as a major pathomechanism in OPA1-associated adOA.

Single-base substitution at the last nucleotide of exon 6 (c.671G>A), resulting in the skipping of exon 6, and exons 6 and 7 in human succinyl-CoA:3-ketoacid CoA transferase (SCOT) gene

Succinyl-CoA:3-ketoacid CoA transferase (SCOT, EC 2.8.3.5) is the key enzyme for ketone body utilization. Hereditary SCOT deficiency (MIM 245050) causes episodes of severe ketoacidosis. We identified a homozygous point mutation (c.671G>A) , which is a single-base substitution at the last nucleotide of exon 6, in a Turkish patient (GS12) with SCOT deficiency. This point mutation resulted in the skipping of exon 6, and exons 6 and 7 in human SCOT genes. To understand why the c.671G>A causes exons 6 and 7 skipping, nuclear RNA was separated from cytoplasmic RNA and both were analyzed by RT-PCR. In nuclear RNA, SCOT mRNA with exon 6 skipping was predominant and mRNA with exons 6 and 7 skipping was hardly detected, whereas the latter became one of major mRNA species in cytoplasmic RNA. This discrepancy was interpreted as follows: exon 6 skipping causes a frameshift and nonsense-mediated RNA decay in the cytosol, so mRNA with exon 6 skipping was unstable. On the other hand, SCOT mRNA with exons 6 and 7 is a minor transcript but it retains the reading-frame and is stable in cytosol. As a result, the latter mRNA is more abundant under steady-state conditions as compared to the former mRNA.

A novel type 2A von Willebrand factor mutation located at the last nucleotide of exon 26 (3538G>A) causes skipping of 2 nonadjacent exons

In this manuscript, we describe a case of type 2A von Willebrand disease (VWD) caused by the novel heterozygous G&gt;A transition at nucleotide 3538, which should result in the putative, nonconservative substitution of G1180R. This mutation was reproduced by site-directed mutagenesis; however, the recombinant mutant protein was efficiently secreted from cells and assembled correctly into multimers. Because the substitution is located at the last nucleotide of exon 26, the patient's platelet von Willebrand factor (VWF) mRNA was analyzed and 3 transcripts were observed: the normal transcript without the 3538G&gt;A transition, a transcript with the in-frame deletion of exon 26, and a transcript with the in-frame deletions of exons 23 and 26. These deletion VWF cDNA constructs were created and the resulting recombinant proteins were analyzed following transfection into COS-7 cells. Cotransfection results demonstrate that the exon-skipped transcripts led to intracellular retention, and the levels of VWF antigen (VWF:Ag) produced by these constructs were as follows: del23/26&lt;del26&lt; G1180R≤wild type. The homozygous exon-skipped transcripts show the presence of only the lowest molecular weight multimers. The G&gt;A transition at nucleotide (nt) 3538 does not result in the expression of the G1180R missense mutation, but rather leads to exon skipping, which is the pathogenic basis of the patient's phenotype. This is the first report of a coding region mutation resulting in the skipping of 2 nonadjacent exons. (Blood. 2004;104:2739-2745)

Identification of novel pro-alpha2(IX) collagen gene mutations in two families with distinctive oligo-epiphyseal forms of multiple epiphyseal dysplasia

Multiple epiphyseal dysplasia (MED) is a genetically heterogeneous disorder with marked clinical and radiographic variability. Traditionally, the mild "Ribbing" and severe "Fairbank" types have been used to define a broad phenotypic spectrum. Mutations in the gene encoding cartilage oligomeric-matrix protein have been shown to result in several types of MED, whereas mutations in the gene encoding the alpha2 chain of type IX collagen (COL9A2) have so far been found only in two families with the Fairbank type of MED. Type IX collagen is a heterotrimer of pro-alpha chains derived from three distinct genes-COL9A1, COL9A2, and COL9A3. In this article, we describe two families with distinctive oligo-epiphyseal forms of MED, which are heterozygous for different mutations in the COL9A2 exon 3/intron 3 splice-donor site. Both of these mutations result in the skipping of exon 3 from COL9A2 mRNA, but the position of the mutation in the splice-donor site determines the stability of the mRNA produced from the mutant COL9A2 allele.

Hereditary skin diseases of anchoring fibrils

Remarkable progress has been made in the last few years in understanding the functions of the anchoring fibrils, polymers of collagen VII, that connect the epidermal basement membrane with the dermal connective tissue. Novel insights into the biology of these fibrils have been gained from studies on dystrophic epidermolysis bullosa (DEB), a group of inherited blistering disorders caused by abnormalities of the anchoring fibrils. Mutations in the COL7A1 gene encoding collagen VII have been disclosed in a number of DEB families, and the mutation analyses and studies on genotype-phenotype correlations in DEB have revealed an unusual complexity of the gene defects and their biological consequences. In analogy to heritable disorders of other collagen genes, predictable phenotypes of COL7A1 mutations causing premature termination codons (PTC) or dominant negative interference have been observed. However, collagen VII seems to be unique among collagens in that many mutations lead to minimal phenotypes, or to no phenotype at all. Furthermore, the mild DEB phenotypes can be severely modulated by a second mutation in individuals compound heterozygous for two different COL7A1 defects. Therefore, not only definition of mutations with diagnostic analyses, but also cell biological, protein chemical and suprastructural studies of the mutated molecules are required for understanding the pathomechanisms underlying DEB.

Facial development and type III collagen RNA expression: concurrent repression in the osteopetrotic (Toothless,tl) rat and rescue after treatment with colony-stimulating factor-1

The toothless (osteopetrotic) mutation in the rat is characterized by retarded development of the anterior facial skeleton. Growth of the anterior face in rats occurs at the premaxillary-maxillary suture (PMMS). To identify potential mechanisms for stunted facial growth in this mutation we compared the temporospatial expression of collagen I (Col I) and collagen III (Col III) RNA around this suture in toothless (tl) rats and normal littermates by in situ hybridization of specific riboprobes in sagittal sections of the head. In normal rats, the suture is S shaped at birth and becomes highly convoluted by 10 days with cells in the center (fibroblasts and osteoblast progenitors) expressing Col III RNA and those at the periphery (osteoblasts) expressing no Col III RNA but high amounts of Col I RNA throughout the growth phase (the first 2 postnatal weeks). In the mutant PMMS, cells were reduced in number, less differentiated, and fewer osteoblasts were encountered. Expression of Col I RNA was at normal levels, but centrosutural cells expressed Col III RNA only after day 6 and then only weakly. A highly convoluted sutural shape was never achieved in mutants during the first 2 postnatal weeks. Treatment of tl rats with the cytokine CSF-1 improved facial growth and restored cellular diversity and Col III RNA expression in the PMMS to normal levels. Taken together, these data suggest that normal facial growth in rats is related to expression of Col III RNAby osteoblast precursors in the PMMS, that these cells are deficient in the tl mutation and are rescued following treatment with CSF-1.

Biology of anchoring fibrils: lessons from dystrophic epidermolysis bullosa

Anchoring fibrils are adhesive suprastructures that ensure the connection of the epidermal basement membrane with the dermal extracellular matrix. The fibrils represent polymers of collagen VII, the major structural fibril component, but may also contain other proteins. Remarkable progress has been made in the last few years in understanding the functions of skin basement membrane components including the anchoring fibrils. Novel insights into the biology of the anchoring fibrils have been gained from experimental studies on dystrophic epidermolysis bullosa (DEB), a group of inherited blistering disorders caused by mutations in the gene for collagen VII, COL7A1. Mutation analyses of DEB families have disclosed more than 100 COL7A1 gene defects so far, but the unusual complexity of the mutation constellations and their biological consequences are only beginning to emerge. In analogy to heritable disorders of other collagen genes, predictable phenotypes of COL7A1 mutations causing premature termination codons or dominant negative interference have been observed. However, collagen VII seems to represent a remarkable exception among collagens in that many mutations, including heterozygous glycine substitutions and deletions, lead to minimal phenotypes, or to no phenotype at all. In contrast to fibrillar collagens, structural abnormalities of collagen VII molecules in anchoring fibrils appear to be tolerated to a certain extent. However, the mild DEB phenotypes can be severely modulated by a second aberration in individuals compound heterozygous for two different COL7A1 mutations. Therefore, not only definition of mutation(s) but also cell biological, protein chemical and suprastructural studies of the mutated molecules yield novel insight into the molecular pathomechanisms underlying disease.

A novel Arg362Ser mutation in the sterol 27-hydroxylase gene (CYP27): its effects on pre-mRNA splicing and enzyme activity

A novel C to A mutation in the sterol 27-hydroxylase gene (CYP27) was identified by sequencing amplified CYP27 gene products from a patient with cerebrotendinous xanthomatosis (CTX). The mutation changed the adrenodoxin cofactor binding residue 362Arg to 362Ser (CGT 362Arg to AGT 362Ser), and was responsible for deficiency in the sterol 27-hydroxylase activity, as confirmed by expression of mutant cDNA into COS-1 cells. Quantitative analysis showed that the expression of CYP27 gene mRNA in the patient represented 52.5% of the normal level. As the mutation occurred at the penultimate nucleotide of exon 6 (-2 position of exon 6-intron 6 splice site) of the gene, we hypothesized that the mutation may partially affect the normal splicing efficiency in exon 6 and cause alternative splicing elsewhere, which resulted in decreased transcript in the patient. Transfection of constructed minigenes, with or without the mutation, into COS-1 cells confirmed that the mutant minigene was responsible for a mRNA species alternatively spliced at an activated cryptic 5' splice site 88 bp upstream from the 3' end of exon 6. Our data suggest that the C to A mutation at the penultimate nucleotide of exon 6 of the CYP27 gene not only causes the deficiency in the sterol 27-hydroxylase activity, but also partially leads to alternative pre-mRNA splicing of the gene. To our knowledge, this is the first report regarding effects on pre-mRNA splicing of a mutation at the -2 position of a 5' splice site.

Deletions within COL7A1 exons distant from consensus splice sites alter splicing and produce shortened polypeptides in dominant dystrophic epidermolysis bullosa

We describe two familial cases of dominant dystrophic epidermolysis bullosa (DDEB) that are heterozygous for deletions in COL7A1 that alter splicing, despite intact consensus splice-site sequences. One patient shows a 28-bp genomic deletion (6081del28) in exon 73 associated with the activation of a cryptic donor splice site within this exon; the combination of both defects restores the phase and replaces the last 11 Gly-X-Y repeats of exon 73 by a noncollagenous sequence, Glu-Ser-Leu. The second patient demonstrates a 27-bp deletion in exon 87 (6847del27), causing in-frame skipping of this exon; consensus splice sites, putative branch sites, and introns flanking exons 73 and 87 showed a normal sequence. Keratinocytes from the probands synthesized normal and shortened type VII collagen polypeptides and showed intracellular accumulation of type VII procollagen molecules. This first report of genomic deletions in COL7A1 in DDEB suggests a role for exonic sequences in the control of splicing of COL7A1 pre-mRNA and provides evidence that shortened type VII collagen polypeptides can alter, in a dominant manner, anchoring-fibril formation and can cause DDEB of differing severity.

Splicing defects in the COL3A1 gene: marked preference for 5' (donor) spice-site mutations in patients with exon-skipping mutations and Ehlers-Danlos syndrome type IV

Ehlers-Danlos syndrome (EDS) type IV results from mutations in the COL3A1 gene, which encodes the constituent chains of type III procollagen. We have identified, in 33 unrelated individuals or families with EDS type IV, mutations that affect splicing, of which 30 are point mutations at splice junctions and 3 are small deletions that remove splice-junction sequences and partial exon sequences. Except for one point mutation at a donor site, which leads to partial intron inclusion, and a single base-pair substitution at an acceptor site, which gives rise to inclusion of the complete upstream intron into the mature mRNA, all mutations result in deletion of a single exon as the only splice alteration. Of the exon-skipping mutations that are due to single base substitutions, which we have identified in 28 separate individuals, only two affect the splice-acceptor site. The underrepresentation of splice acceptor-site mutations suggests that the favored consequence of 3' mutations is the use of an alternative acceptor site that creates a null allele with a premature-termination codon. The phenotypes of those mutations may differ, with respect to either their severity or their symptomatic range, from the usual presentation of EDS type IV and thus have been excluded from analysis.

Juvenile hyaline fibromatosis: impaired collagen metabolism in human skin fibroblasts

Juvenile hyaline fibromatosis (JHF) is inherited as a fatal autosomal recessive disorder characterised by multiple tumorous mucocutaneous proliferations. In this paper a 14 month old girl with JHF is described. For this condition, a malfunction of collagen synthesis is considered as the pathogenetic cause. Recently published data have revealed an absent band for type III collagen (TIIIC) chain in western blot studies of clinically unaffected JHF skin. Therefore supernatants of skin fibroblast cell cultures, obtained from normal human skin, were analysed for type 1 collagen (TIC) and TIIIC metabolites by radioimmunoassays. Besides the typical morphological connective tissue changes in the skin lesions, TIC synthesis and degradation were found increased in JHF fibroblasts compared with control fibroblasts. In contrast, TIIIC overall metabolism was significantly reduced by 36% compared with controls.

The autosomal recessive isolated deafness, DFNB2, and the Usher 1B syndrome are allelic defects of the myosin-VIIA gene

Hereditary non-syndromic profound deafness affects about 1 in 2000 children prior to language acquisition. In 80% of the cases, the mode of transmission is autosomal recessive. The number of genes involved in these recessive forms of isolated deafness (DFNB genes) has been estimated to between 30 and 100. So far, ten DFNB genes have been mapped to human chromosomes, one of which has been isolated. By linkage analysis of a single family whose members were affected with profound deafness, some of them presenting with vestibular dysfunction, DFNB2 has been mapped to chromosome 11q13 (ref. 3). The gene responsible for a form of Usher syndrome type I, USH1B, has been assigned to the same chromosomal region. Usher syndrome associates profound congenital deafness and vestibular dysfunction with retinitis pigmentosa. In the homologous murine region are located the shaker-1 mutations responsible for deafness and vestibular dysfunction. It has been demonstrated that the murine shaker-1 and human USH1B phenotypes result from mutations in the gene encoding myosin-VIIA. Based on mapping data as well as on the similarities between the phenotypes of DFNB2-affected patients and shaker-1 mouse mutants, we have proposed that a defective myosin-VIIA may also be responsible for DFNB2 (ref. 1). Sequence analysis of each of the coding exons of the myosin-VIIA gene (MYO7A) was thus undertaken in the DFNB2-affected family. In the last nucleotide of exon 15, a G to A transition was detected, a type of mutation that is known to decrease the efficiency of splicing. Accordingly, this result shows that different mutations in MYO7A result in either an isolated or a syndromic form of deafness.

Ehlers-Danlos syndrome has varied molecular mechanisms

Images

Type III collagen is crucial for collagen I fibrillogenesis and for normal cardiovascular development

Type III collagen is a fibrillar forming collagen comprising three alpha1(III) chains and is expressed in early embryos and throughout embryogenesis. In the adult, type III collagen is a major component of the extracellular matrix in a variety of internal organs and skin. Mutations in the COL3A1 gene have been implicated as a cause of type IV Ehlers-Danlos syndrome, a disease leading to aortic rupture in early adult life. To directly study the role of Col3a1 in development and disease, we have inactivated the Col3a1 gene in embryonic stem cells by homologous recombination. The mutated allele was transmitted through the mouse germ line and homozygous mutant animals were derived from heterozygous intercrosses. About 10% of the homozygous mutant animals survived to adulthood but have a much shorter life span compared with wild-type mice. The major cause of death of mutant mice was rupture of the major blood vessels, similar to patients with type IV Ehlers-Danlos syndrome. Ultrastructural analysis of tissues from mutant mice revealed that type III collagen is essential for normal collagen I fibrillogenesis in the cardiovascular system and other organs.

Mutations in the COL3A1 gene result in the Ehlers-Danlos syndrome type IV and alterations in the size and distribution of the major collagen fibrils of the dermis

Ehlers-Danlos syndrome type IV (EDS type IV) results from heterozygosity for mutations in the COL3A1 gene that encodes the chains of type III procollagen. By using light, transmission, and scanning electron microscopy, we examined skin biopsies from 22 individuals with EDS type IV in whom the COL3A1 mutations had been identified. The most striking changes in EDS type IV were correlated with point mutations that substituted a residue for a glycine near the carboxyl-terminal end of the triple-helical domain of pro alpha1(III). In three cases with the mutation G1012R, G1018V, or G1021E, cells in the dermis had extremely dilated rough endoplasmic reticulum (RER), the dermis was thin, and there was a reduced proportion of collagen although the proportion of elastic fibers appeared increased. In these tissues, collagen fibrils were small (65-80 nm) compared to normal (95-110 nm). Fibrils 80-90 nm in diameter and moderately dilated RER were found with mutations G769R, G373R, and G061E and with exon-skipping mutations of exons 34 and 45. With mutations G034R and G016C and exon-skipping mutations that deleted the sequences of exons 7, 8, 14, 18, 24, and 27, fibrils were more variable in size (85-120 nm). The composite collagen fibrils characteristic of EDS types I and II were not found in EDS type IV. These findings indicate that mutations in the COL3A1 gene have effects on secretion, fibrillogenesis, and skin architecture that reflect the position and nature of the mutation.

Abnormal extracellular matrix in Ehlers-Danlos syndrome type IV due to the substitution of glycine 934 by glutamic acid in the triple helical domain of type III collagen

A unique substitution of glycine 934 by glutamic acid in the triple helical domain of type III collagen was identified in a proband with Ehlers-Danlos syndrome type IV. The substitution was due to the transition of G 3302 to A in alpha 1(III) cDNA which is encoded by exon 46 of COL3A1. It resulted in a severe deficiency of type III collagen in fibroblast cultures and dermis. Dilatation of the endoplasmic reticulum of the dermal fibroblasts was probably due to the failure of these cells to secrete type III collagen molecules containing one or more mutant alpha 1(III) chains. The dermal collagen fibrils were narrow, but their constituent type III collagen molecules contained predominantly normal alpha 1(III) chains. As a results, the major effect of the substitution of glycine 934 by glutamic acid was to severely reduce the amount of normal type III collagen available for the formation of heterotypic collagen fibrils in the extracellular matrix.