Tenascin-X deficiency mimics Ehlers-Danlos syndrome in mice through alteration of collagen deposition

Tenascin-X is a large extracellular matrix protein of unknown function. Tenascin-X deficiency in humans is associated with Ehlers-Danlos syndrome, a generalized connective tissue disorder resulting from altered metabolism of the fibrillar collagens. Because TNXB is the first Ehlers-Danlos syndrome gene that does not encode a fibrillar collagen or collagen-modifying enzyme, we suggested that tenascin-X might regulate collagen synthesis or deposition. To test this hypothesis, we inactivated Tnxb in mice. Tnxb-/- mice showed progressive skin hyperextensibility, similar to individuals with Ehlers-Danlos syndrome. Biomechanical testing confirmed increased deformability and reduced tensile strength of their skin. The skin of Tnxb-/- mice was histologically normal, but its collagen content was significantly reduced. At the ultrastructural level, collagen fibrils of Tnxb-/- mice were of normal size and shape, but the density of fibrils in their skin was reduced, commensurate with the reduction in collagen content. Studies of cultured dermal fibroblasts showed that although synthesis of collagen I by Tnxb-/- and wildtype cells was similar, Tnxb-/- fibroblasts failed to deposit collagen I into cell-associated matrix. This study confirms a causative role for TNXB in human Ehlers-Danlos syndrome and suggests that tenascin-X is an essential regulator of collagen deposition by dermal fibroblasts.     

Evidence for a relationship between Ehlers-Danlos type VII C in humans and bovine dermatosparaxis.

Ehlers-Danlos (ED) syndrome type VII is characterized by the accumulation of collagen precursors in connective tissues. ED VII A and B are caused by mutations in the genes of alpha 1 and alpha 2 collagen I which result in the disruption of the cleavage site of procollagen I N-proteinase. The existence of ED VII C in humans has been hypothesized on the basis of a disorder in cattle and sheep related to the absence of the enzyme. We now present evidence for the existence of this disease in humans, characterized by skin fragility, altered polymers seen as hieroglyphic pictures with electron microscopy, accumulation of p-N-alpha 1 and p-N-alpha 2 collagen type I in the dermis and absence of processing of the p-N-I polypeptides in fibroblast cultures.     

Mutations in COL11A2 cause non-syndromic hearing loss (DFNA13)

We report that mutation of COL11A2 causes deafness previously mapped to the DFNA13 locus on chromosome 6p. We found two families (one American and one Dutch) with autosomal dominant, non-syndromic hearing loss to have mutations in COL11A2 that are predicted to affect the triple-helix domain of the collagen protein. In both families, deafness is non-progressive and predominantly affects middle frequencies. Mice with a targeted disruption of Col11a2 also were shown to have hearing loss. Electron microscopy of the tectorial membrane of these mice revealed loss of organization of the collagen fibrils. Our findings revealed a unique ultrastructural malformation of inner-ear architecture associated with non-syndromic hearing loss, and suggest that tectorial membrane abnormalities may be one aetiology of sensorineural hearing loss primarily affecting the mid-frequencies.     

An aspartic acid repeat polymorphism in asporin inhibits chondrogenesis and increases susceptibility to osteoarthritis

Osteoarthritis is the most common form of human arthritis. We investigated the potential role of asporin, an extracellular matrix component expressed abundantly in the articular cartilage of individuals with osteoarthritis, in the pathogenesis of osteoarthritis. Here we report a significant association between a polymorphism in the aspartic acid (D) repeat of the gene encoding asporin (ASPN) and osteoarthritis. In two independent populations of individuals with knee osteoarthritis, the D14 allele of ASPN is over-represented relative to the common D13 allele, and its frequency increases with disease severity. The D14 allele is also over-represented in individuals with hip osteoarthritis. Asporin suppresses TGF-beta-mediated expression of the genes aggrecan (AGC1) and type II collagen (COL2A1) and reduced proteoglycan accumulation in an in vitro model of chondrogenesis. The effect on TGF-beta activity is allele-specific, with the D14 allele resulting in greater inhibition than other alleles. In vitro binding assays showed a direct interaction between asporin and TGF-beta. Taken together, these findings provide another functional link between extracellular matrix proteins, TGF-beta activity and disease, suggesting new therapeutic strategies for osteoarthritis.     

Mutations in ABCC6 cause pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a heritable disorder of the connective tissue. PXE patients frequently experience visual field loss and skin lesions, and occasionally cardiovascular complications. Histopathological findings reveal calcification of the elastic fibres and abnormalities of the collagen fibrils. Most PXE patients are sporadic, but autosomal recessive and dominant inheritance are also observed. We previously localized the PXE gene to chromosome 16p13.1 (refs 8,9) and constructed a physical map. Here we describe homozygosity mapping in five PXE families and the detection of deletions or mutations in ABCC6 (formerly MRP6) associated with all genetic forms of PXE in seven patients or families.     

Herpesvirus vector gene transfer and expression of beta-glucuronidase in the central nervous system of MPS VII mice.

Genetic disorders affecting the central nervous system (CNS) can potentially be treated by gene transfer using vectors which infect and express genes in post-mitotic neurons. Herpesviruses establish latent infections in neurons during which only one viral gene (LAT) is expressed, thus the LAT promoter may express foreign genes in latently infected CNS cells. Expression of a beta-glucuronidase gene driven by the LAT promoter was tested in mice lacking this enzyme, which are a model for a human genetic disease affecting the CNS (mucopolysaccharidosis VII, Sly disease). Cells expressing the missing enzymatic activity were present in the trigeminal ganglia and brainstems of latently infected animals, up to four months post-inoculation, demonstrating the potential of this approach for the long-term expression of foreign genes in the CNS.     

An epi-allelic series of p53 hypomorphs created by stable RNAi produces distinct tumor phenotypes in vivo

The application of RNA interference (RNAi) to mammalian systems has the potential to revolutionize genetics and produce novel therapies. Here we investigate whether RNAi applied to a well-characterized gene can stably suppress gene expression in hematopoietic stem cells and produce detectable phenotypes in mice. Deletion of the Trp53 tumor suppressor gene greatly accelerates Myc-induced lymphomagenesis, resulting in highly disseminated disease. To determine whether RNAi suppression of Trp53 could produce a similar phenotype, we introduced several Trp53 short hairpin RNAs (shRNAs) into hematopoietic stem cells derived from E(mu)-Myc transgenic mice, and monitored tumor onset and overall pathology in lethally irradiated recipients. Different Trp53 shRNAs produced distinct phenotypes in vivo, ranging from benign lymphoid hyperplasias to highly disseminated lymphomas that paralleled Trp53-/- lymphomagenesis in the E(mu)-Myc mouse. In all cases, the severity and type of disease correlated with the extent to which specific shRNAs inhibited p53 activity. Therefore, RNAi can stably suppress gene expression in stem cells and reconstituted organs derived from those cells. In addition, intrinsic differences between individual shRNA expression vectors targeting the same gene can be used to create an 'epi-allelic series' for dissecting gene function in vivo.     

Adenovirus-mediated in vivo gene transfer and expression in normal rat liver.

Replication deficient, recombinant adenovirus (Ad) vectors do not require target cell replication for transfer and expression of exogenous genes and thus may be useful for in vivo gene therapy in hepatocytes. In vitro, primary cultures of rat hepatocytes infected with a recombinant Ad containing a human alpha 1-antitrypsin cDNA (Ad-alpha 1AT) synthesized and secreted human alpha 1AT for 4 weeks. In rats, in vivo intraportal administration of a recombinant Ad containing the E. coli lacZ gene, was followed by expression of beta-galactosidase in hepatocytes 3 days after infection. Intraportal infusion of Ad-alpha 1AT produced detectable serum levels of human alpha 1AT for 4 weeks. Thus, targeted gene expression has been achieved in the liver, albeit at low levels, suggesting that adenovirus vectors may be a useful means for in vivo gene therapy in liver disorders.     

Treatment-specific changes in gene expression discriminate in vivo drug response in human leukemia cells

To elucidate the genomics of cellular responses to cancer treatment, we analyzed the expression of over 9,600 human genes in acute lymphoblastic leukemia cells before and after in vivo treatment with methotrexate and mercaptopurine given alone or in combination. Based on changes in gene expression, we identified 124 genes that accurately discriminated among the four treatments. Discriminating genes included those involved in apoptosis, mismatch repair, cell cycle control and stress response. Only 14% of genes that changed when these medications were given as single agents also changed when they were given together. These data indicate that lymphoid leukemia cells of different molecular subtypes share common pathways of genomic response to the same treatment, that changes in gene expression are treatment-specific and that gene expression can illuminate differences in cellular response to drug combinations versus single agents.     

Somatic integration and long-term transgene expression in normal and haemophilic mice using a DNA transposon system

The development of non-viral gene-transfer technologies that can support stable chromosomal integration and persistent gene expression in vivo is desirable. Here we describe the successful use of transposon technology for the nonhomologous insertion of foreign genes into the genomes of adult mammals using naked DNA. We show that the Sleeping Beauty transposase can efficiently insert transposon DNA into the mouse genome in approximately 5-6% of transfected mouse liver cells. Chromosomal transposition resulted in long-term expression (>5 months) of human blood coagulation factor IX at levels that were therapeutic in a mouse model of haemophilia B. Our results establish DNA-mediated transposition as a new genetic tool for mammals, and provide new strategies to improve existing non-viral and viral vectors for human gene therapy applications.     

Mutational and functional analyses reveal that ST7 is a highly conserved tumor-suppressor gene on human chromosome 7q31

Loss of heterozygosity (LOH) of markers on human chromosome 7q31 is frequently encountered in a variety of human neoplasias, indicating the presence of a tumor-suppressor gene (TSG). By a combination of microcell-fusion and deletion-mapping studies, we previously established that this TSG resides within a critical region flanked by the genetic markers D7S522 and D7S677. Using a positional cloning strategy and aided by the availability of near-complete sequence of this genomic interval, we have identified a TSG within 7q31, named ST7 (for suppression of tumorigenicity 7; this same gene was recently reported in another context and called RAY1). ST7 is ubiquitously expressed in human tissues. Analysis of a series of cell lines derived from breast tumors and primary colon carcinomas revealed the presence of mutations in ST7. Introduction of the ST7 cDNA into the prostate-cancer-derived cell line PC3 had no effect on the in vitro proliferation of the cells, but abrogated their in vivo tumorigenicity. Our data indicate that ST7 is a TSG within chromosome 7q31 and may have an important role in the development of some types of human cancer.     

Mutations in the region encoding the von Willebrand factor A domain of matrilin-3 are associated with multiple epiphyseal dysplasia

Multiple epiphyseal dysplasia (MED) is a relatively mild and clinically variable osteochondrodysplasia, primarily characterized by delayed and irregular ossification of the epiphyses and early-onset osteoarthritis. Mutations in the genes encoding cartilage oligomeric matrix protein (COMP) and type IX collagen (COL9A2 and COL9A3) have previously been shown to cause different forms of MED (refs. 4-13). These dominant forms of MED (EDM1-3) are caused by mutations in the genes encoding structural proteins of the cartilage extracellular matrix (ECM); these proteins interact with high affinity in vitro. A recessive form of MED (EDM4) has also been reported; it is caused by a mutation in the diastrophic dysplasia sulfate transporter gene (SLC26A). A genomewide screen of family with autosomal-dominant MED not linked to the EDM1-3 genes provides significant genetic evidence for a MED locus on the short arm of chromosome 2 (2p24-p23), and a search for candidate genes identified MATN3 (ref. 18), encoding matrilin-3, within the critical region. Matrilin-3 is an oligomeric protein that is present in the cartilage ECM. We have identified two different missense mutations in the exon encoding the von Willebrand factor A (vWFA) domain of matrilin-3 in two unrelated families with MED (EDM5). These are the first mutations to be identified in any of the genes encoding the matrilin family of proteins and confirm a role for matrilin-3 in the development and homeostasis of cartilage and bone.     

The role of the transcriptional regulator Ptf1a in converting intestinal to pancreatic progenitors

Pancreas development begins with the formation of buds at specific sites in the embryonic foregut endoderm. We used recombination-based lineage tracing in vivo to show that Ptf1a (also known as PTF1-p48) is expressed at these early stages in the progenitors of pancreatic ducts, exocrine and endocrine cells, rather than being an exocrine-specific gene as previously described. Moreover, inactivation of Ptf1a switches the character of pancreatic progenitors such that their progeny proliferate in and adopt the normal fates of duodenal epithelium, including its stem-cell compartment. Consistent with the proposal that Ptf1a supports the specification of precursors of all three pancreatic cell types, transgene-based expression of Pdx1, a gene essential to pancreas formation, from Ptf1a cis-regulatory sequences restores pancreas tissue to Pdx1-null mice that otherwise lack mature exocrine and endocrine cells because of an early arrest in organogenesis. These experiments provide evidence that Ptf1a expression is specifically connected to the acquisition of pancreatic fate by undifferentiated foregut endoderm.     

Perlecan is essential for cartilage and cephalic development.

Perlecan, a large, multi-domain, heparan sulfate proteoglycan originally identified in basement membrane, interacts with extracellular matrix proteins, growth factors and receptors, and influences cellular signalling. Perlecan is present in a variety of basement membranes and in other extracellular matrix structures. We have disrupted the gene encoding perlecan (Hspg2) in mice. Approximately 40% of Hspg2-/- mice died at embryonic day (E) 10.5 with defective cephalic development. The remaining Hspg2-/- mice died just after birth with skeletal dysplasia characterized by micromelia with broad and bowed long bones, narrow thorax and craniofacial abnormalities. Only 6% of Hspg2-/- mice developed both exencephaly and chondrodysplasia. Hspg2-/- cartilage showed severe disorganization of the columnar structures of chondrocytes and defective endochondral ossification. Hspg2-/- cartilage matrix contained reduced and disorganized collagen fibrils and glycosaminoglycans, suggesting that perlecan has an important role in matrix structure. In Hspg2-/- cartilage, proliferation of chondrocytes was reduced and the prehypertrophic zone was diminished. The abnormal phenotypes of the Hspg2-/- skeleton are similar to those of thanatophoric dysplasia (TD) type I, which is caused by activating mutations in FGFR3 (refs 7, 8, 9), and to those of Fgfr3 gain-of-function mice. Our findings suggest that these molecules affect similar signalling pathways.     

Kras regulatory elements and exon 4A determine mutation specificity in lung cancer

Kras is the most frequently mutated ras family member in lung carcinomas, whereas Hras mutations are common in tumors from stratified epithelia such as the skin. Using a Hras knock-in mouse model, we demonstrate that specificity for Kras mutations in lung and Hras mutations in skin tumors is determined by local regulatory elements in the target ras genes. Although the Kras 4A isoform is dispensable for mouse development, it is the most important isoform for lung carcinogenesis in vivo and for the inhibitory effect of wild-type (WT) Kras on the mutant allele. Kras 4A expression is detected in a subpopulation of normal lung epithelial cells, but at very low levels in lung tumors, suggesting that it may not be required for tumor progression. The two Kras isoforms undergo different post-translational modifications; therefore, these findings can have implications for the design of therapeutic strategies for inhibiting oncogenic Kras activity in human cancers.