Showing papers in "Nature Genetics in 1997"
TL;DR: The results identify a strong candidate tumour suppressor gene at chromosome 10q23.3, whose loss of function appears to be associated with the oncogenesis of multiple human cancers.
Abstract: Deletions involving regions of chromosome 10 occur in the vast majority (> 90%) of human glioblastoma multiformes. A region at chromosome 10q23-24 was implicated to contain a tumour suppressor gene and the identification of homozygous deletions in four glioma cell lines further refined the location. We have identified a gene, designated MMAC1, that spans these deletions and encodes a widely expressed 5.5-kb mRNA. The predicted MMAC1 protein contains sequence motifs with significant homology to the catalytic domain of protein phosphatases and to the cytoskeletal proteins, tensin and auxilin. MMAC1 coding-region mutations were observed in a number of glioma, prostate, kidney and breast carcinoma cell lines or tumour specimens. Our results identify a strong candidate tumour suppressor gene at chromosome 10q23.3, whose loss of function appears to be associated with the oncogenesis of multiple human cancers.
2,777 citations
TL;DR: Mutational analysis of PTEN in CD kindreds has identified germline mutations that are predicted to disrupt the protein tyrosine/dual-specificity phosphatase domain of this gene, and implies that PTEN may play a role in organizing the relationship of different cell types within an organ during development.
Abstract: Cowden disease (CD) is an autosomal dominant cancer predisposition syndrome associated with an elevated risk for tumours of the breast, thyroid and skin1–2. Lhermitte-Duclos disease (LDD) cosegregates with a subset of CD families and is associated with macrocephaly, ataxia and dysplastic cerebellar gangliocytomatosis3–4. The common feature of these diseases is a predisposition to hamartomas, benign tumours containing differentiated but disorganized cells indigenous to the tissue of origin. Linkage analysis has determined that a single locus within chromosome 10q23 is likely to be responsible for both of these diseases5. A candidate tumour suppressor gene (PTEN) within this region is mutated in sporadic brain, breast and prostate cancer6. Another group has independently isolated the same gene, termed MMAC1, and also found somatic mutations throughout the gene in advanced sporadic cancers7. Mutational analysis of PTEN in CD kindreds has identified germline mutations in four of five families. We found nonsense and missense mutations that are predicted to disrupt the protein tyrosine/dual-specificity phosphatase domain of this gene. Thus, PTEN appears to behave as a tumour suppressor gene in the germline. Our data also imply that PTEN may play a role in organizing the relationship of different cell types within an organ during development.
2,000 citations
TL;DR: The discovery of a gene that codes for a novel uncoupling protein, designated UCP2, which has 59% amino-acid identity to UCP1, is reported, and properties consistent with a role in diabetes and obesity are described, suggesting that U CP2 has a unique role in energy balance, body weight regulation and thermoregulation and their responses to inflammatory stimuli.
Abstract: A mitochondrial protein called uncoupling protein (UCP1) plays an important role in generating heat and burning calories by creating a pathway that allows dissipation of the proton electrochemical gradient across the inner mitochondrial membrane in brown adipose tissue, without coupling to any other energy-consuming process. This pathway has been implicated in the regulation of body temperature, body composition and glucose metabolism. However, UCP1-containing brown adipose tissue is unlikely to be involved in weight regulation in adult large-size animals and humans living in a thermoneutral environment (one where an animal does not have to increase oxygen consumption or energy expenditure to lose or gain heat to maintain body temperature), as there is little brown adipose tissue present. We now report the discovery of a gene that codes for a novel uncoupling protein, designated UCP2, which has 59% amino-acid identity to UCP1, and describe properties consistent with a role in diabetes and obesity. In comparison with UCP1, UCP2 has a greater effect on mitochondrial membrane potential when expressed in yeast. Compared to UCP1, the gene is widely expressed in adult human tissues, including tissues rich in macrophages, and it is upregulated in white fat in response to fat feeding. Finally, UCP2 maps to regions of human chromosome 11 and mouse chromosome 7 that have been linked to hyperinsulinaemia and obesity. Our findings suggest that UCP2 has a unique role in energy balance, body weight regulation and thermoregulation and their responses to inflammatory stimuli.
1,667 citations
TL;DR: It is concluded that a small polyglutamine expansion in the human α1A calcium channel is most likely the cause of a newly classified autosomal dominant spinocerebellar ataxia, SCA6.
Abstract: A polymorphic CAG repeat was identified in the human α1A voltage-dependent calcium channel subunit. To test the hypothesis that expansion of this CAG repeat could be the cause of an inherited progressive ataxia, we genotyped a large number of unrelated controls and ataxia patients. Eight unrelated patients with late onset ataxia had alleles with larger repeat numbers (21‐27) compared to the number of repeats (4‐16) in 475 non‐ataxia individuals. Analysis of the repeat length in families of the affected individuals revealed that the expansion segregated with the phenotype in every patient. We identified six isoforms of the human α1A calcium channel subunit. The CAG repeat is within the open reading frame and is predicted to encode glutamine in three of the isoforms. We conclude that a small polyglutamine expansion in the human α1A calcium channel is most likely the cause of a newly classified autosomal dominant spinocerebellar ataxia, SCA6.
1,558 citations
TL;DR: It is demonstrated that a mutation in bovine MSTN, which encodes myostatin, a member of the TGFβ superfamily, is responsible for the double-muscled phenotype, and an 11-bp deletion in the coding sequence for the bioactive carboxy-termihal domain of the protein causing the muscular hypertrophy observed in Belgian Blue cattle is reported.
Abstract: An exceptional muscle development commonly referred to as 'double-muscled' (Fig. 1) has been seen in several cattle breeds and has attracted considerable attention from beef producers. Double-muscled animals are characterized by an increase in muscle mass of about 20%, due to general skeletal-muscle hyperplasia-that is, an increase in the number of muscle fibers rather than in their individual diameter. Although the hereditary nature of the double-muscled condition was recognized early on, the precise mode of inheritance has remained controversial; monogenic (domainant and recessive), oligogenic and polygenic models have been proposed. In the Belgian Blue cattle breed (BBCB), segregation analysis performed both in experimental crosses and in the outbred population suggested an autosomal recessive inheritance. This was confirmed when the muscular hypertrophy (mh) locus was mapped 3.1 cM from microsatellite TGLA44 on the centromeric end of bovine chromosome 2 (ref. 5). We used a positional candidate approach to demonstrate that a mutation in bovine MSTN, which encodes myostatin, a member of the TGF beta superfamily, is responsible for the double-muscled phenotype. We report an 11-bp deletion in the coding sequence for the bioactive carboxy-terminal domain of the protein causing the muscular hypertrophy observed in Belgian Blue cattle.
1,486 citations
TL;DR: The results suggest that missense mutations located in the MET proto-oncogene lead to constitutive activation of the MET protein and papillary renal carcinomas.
Abstract: Hereditary papillary renal carcinoma (HPRC) is a recently recognized form of inherited kidney cancer characterized by a predisposition to develop multiple, bilateral papillary renal tumours. The pattern of inheritance of HPRC is consistent with autosomal dominant transmission with reduced penetrance. HPRC is histologically and genetically distinct from two other causes of inherited renal carcinoma, von Hippel-Lindau disease (VHL) and the chromosome translocation (3;8). Malignant papillary renal carcinomas are characterized by trisomy of chromosomes 7, 16 and 17, and in men, by loss of the Y chromosome. Inherited and sporadic clear cell renal carcinomas are characterized by inactivation of both copies of the VHL gene by mutation, and/or by hypermethylation. We found that the HPRC gene was located at chromosome 7q31.1-34 in a 27-centimorgan (cM) interval between D7S496 and D7S1837. We identified missense mutations located in the tyrosine kinase domain of the MET gene in the germline of affected members of HPRC families and in a subset of sporadic papillary renal carcinomas. Three mutations in the MET gene are located in codons that are homologous to those in c-kit and RET, proto-oncogenes that are targets of naturally-occurring mutations. The results suggest that missense mutations located in the MET proto-oncogene lead to constitutive activation of the MET protein and papillary renal carcinomas.
1,392 citations
TL;DR: A minimal co-segregating region of 60 kb containing the FMF gene (MEFV) is defined and one of these transcripts encodes a new protein (marenostrin) related to the ret-finger protein and to butyrophilin.
Abstract: Familial Mediterranean fever (FMF) is an autosomal recessive disorder characterized by attacks of fever and serositis. In this paper, we define a minimal co-segregating region of 60 kb containing the FMF gene (MEFV) and identify four different transcript units within this region. One of these transcripts encodes a new protein (marenostrin) related to the ret-finger protein and to butyrophilin. Four conservative missense variations co-segregating with FMF have been found within the MEFV candidate gene in 85% of the carrier chromosomes. These variations, which cluster at the carboxy terminal domain of the protein, were not present in 308 control chromosomes, including 162 validated non-carriers. We therefore propose that the sequence alterations in the marenostrin protein are responsible for the FMF disease.
1,374 citations
TL;DR: Mutational analysis of ABCR in STGD families revealed a total of 19 different mutations including homozygous mutations in two families with consanguineous parentage, indicating that ABCR is the causal gene of STGD/FFM.
Abstract: Stargardt disease (STGD, also known as fundus flavimaculatus; FFM) is an autosomal recessive retinal disorder characterized by a juvenile-onset macular dystrophy, alterations of the peripheral retina, and subretinal deposition of lipofuscin-like material A gene encoding an ATP-binding cassette (ABC) transporter was mapped to the 2-cM (centiMorgan) interval at 1p13-p21 previously shown by linkage analysis to harbour the STGD gene This gene, ABCR, is expressed exclusively and at high levels in the retina, in rod but not cone photoreceptors, as detected by in situ hybridization Mutational analysis of ABCR in STGD families revealed a total of 19 different mutations including homozygous mutations in two families with consanguineous parentage These data indicate that ABCR is the causal gene of STGD/FFM
1,363 citations
TL;DR: Results indicate that this gene is responsible for the pathogenesis of APECED, a autosomal-recessive disorder that maps to human chromosome 21q22.3 and should facilitate the genetic diagnosis and potential treatment of the disease and enhance the general understanding of the mechanisms underlying autoimmune diseases.
Abstract: Autoimmune polyglandular syndrome type I (APS 1, also called APECED) is an autosomal-recessive disorder that maps to human chromosome 21q22.3 between markers D21S49 and D21S171 by linkage studies. We have isolated a novel gene from this region, AIRE (autoimmune regulator), which encodes a protein containing motifs suggestive of a transcription factor including two zinc-finger (PHD-finger) motifs, a proline-rich region and three LXXLL motifs. Two mutations, a C-->T substitution that changes the Arg 257 (CGA) to a stop codon (TGA) and an A-->G substitution that changes the Lys 83 (AAG) to a Glu codon (GAG), were found in this novel gene in Swiss and Finnish APECED patients. The Arg257stop (R257X) is the predominant mutation in Finnish APECED patients, accounting for 10/12 alleles studied. These results indicate that this gene is responsible for the pathogenesis of APECED. The identification of the gene defective in APECED should facilitate the genetic diagnosis and potential treatment of the disease and further enhance our general understanding of the mechanisms underlying autoimmune diseases.
1,295 citations
TL;DR: To generate animal models for human diseases involving the gonadotropin signal transduction pathway, mice deficient in the FSHβ subunit are produced and therefore in FSH using ES cell technology.
Abstract: Follicle stimulating hormone (FSH) is a member of the glycoprotein hormone family that includes luteinzing hormone (LH), thyroid stimulating hormone, and chorionic gonadotropin. These heterodimeric hormones share a common alpha subunit and differ in their hormone-specific beta subunit. The biological activity is conferred only by the heterodimers. FSH and LH are synthesized in the same cells of the pituitary, the gonadotrophs. FSH receptors are localized to Sertoli cells of the testes and granulosa cells of the ovary. Minimal data has been accumulated so far involving human mutations in the FSH beta, LH beta, or the gonadotropin receptor genes. There are no known mouse strains with mutations in the FSH beta gene. To generate animal models for human diseases involving the gonadotropin signal transduction pathway, we produced mice deficient in the FSH beta subunit and therefore in FSH using ES cell technology. FSH-deficient females are infertile due to a block in folliculogenesis prior to antral follicle formation. Although FSH was predicted to be necessary for spermatogenesis and Sertoli cell growth in males, FSH-deficient males are fertile despite having small testes. Our findings have important implications for male contraceptive development in humans.
1,269 citations
TL;DR: It is demonstrated that UBE3A mutations are one cause of AS and indicate a possible abnormality in ubiquitin-mediated protein degradation during brain development in this disease.
Abstract: Angelman syndrome (AS), characterized by mental retardation, seizures, frequent smiling and laughter, and abnormal gait, is one of the best examples of human disease in which genetic imprinting plays a role. In about 70% of cases, AS is caused by de novo maternal deletions at 15q11-q13 (ref. 2). Approximately 2% of AS cases are caused by paternal uniparental disomy (UPD) of chromosome 15 (ref. 3) and 2-3% are caused by "imprinting mutations'. In the remaining 25% of AS cases, no deletion, uniparental disomy (UPD), or methylation abnormality is detectable, and these cases, unlike deletions or UPD, can be familial. These cases are likely to result from mutations in a gene that is expressed either exclusively or preferentially from the maternal chromosome 15. We have found that a 15q inversion inherited by an AS child from her normal mother disrupts the 5' end of the UBE3A (E6-AP) gene, the product of which functions in protein ubiquitination. We have looked for novel UBE3A mutations in nondeletion/non-UPD/non-imprinting mutation (NDUI) AS patients and have found one patient who is heterozygous for a 5-bp de novo tandem duplication. We have also found in two brothers a heterozygous mutation, an A to G transition that creates a new 3' splice junction 7 bp upstream from the normal splice junction. Both mutations are predicted to cause a frameshift and premature termination of translation. Our results demonstrate that UBE3A mutations are one cause of AS and indicate a possible abnormality in ubiquitin-mediated protein degradation during brain development in this disease.
TL;DR: Four distinct coding mutations in JAG1 are demonstrated, providing evidence that it is the causal gene for Alagille syndrome, and supporting the hypothesis that haploinsufficiency for this gene is one of the mechanisms causing the Alagile syndrome phenotype.
Abstract: Alagille syndrome is an autosomal dominant disorder characterized by abnormal development of liver, heart, skeleton, eye, face and, less frequently, kidney Analyses of many patients with cytogenetic deletions or rearrangements have mapped the gene to chromosome 20p12, although deletions are found in a relatively small proportion of patients (< 7%) We have mapped the human Jagged1 gene (JAG1), encoding a ligand for the developmentally important Notch transmembrane receptor, to the Alagille syndrome critical region within 20p12 The Notch intercellular signalling pathway has been shown to mediate cell fate decisions during development in invertebrates and vertebrates We demonstrate four distinct coding mutations in JAG1 from four Alagille syndrome families, providing evidence that it is the causal gene for Alagille syndrome All four mutations lie within conserved regions of the gene and cause translational frameshifts, resulting in gross alterations of the protein product Patients with cytogenetically detectable deletions including JAG1 have Alagille syndrome, supporting the hypothesis that haploinsufficiency for this gene is one of the mechanisms causing the Alagille syndrome phenotype
TL;DR: A positional cloning strategy is undertaken to identify the causative mutation in mice with microcytic anaemia, and it is suggested that the phenotype is a consequence of a missense mutation in Nramp2 (ref. 5), a previously identified gene of unknown function.
Abstract: Although disorders of iron metabolism are prevalent, iron transport remains poorly understood. To address this problem, we undertook a positional cloning strategy to identify the causative mutation in mice with microcytic anaemia (mk). Homozygous mk/mk mice have microcytic, hypochromic anaemia due to severe defects in intestinal iron absorption and erythroid iron utilization1–4. We report the identification of a strong candidate gene for mk, and suggest that the phenotype is a consequence of a missense mutation in Nramp2 (ref. 5), a previously identified gene of unknown function. Nramp2 is homologous to Nrampl, a gene active in host defense. If Nramp2 is mk, as the cumulative evidence suggests, our findings have broad implications for the understanding of iron transport and resistance to intracellular pathogens.
TL;DR: These studies provide compelling evidence that defects in pendrin cause Pendred syndrome thereby launching a new area of investigation into thyroid physiology, the pathogenesis of congenital deafness and the role of altered sulphate transport in human disease.
Abstract: Pendred syndrome is a recessively inherited disorder with the hallmark features of congenital deafness and thyroid goitre. By some estimates, the disorder may account for upwards of 10% of hereditary deafness. Previous genetic linkage studies localized the gene to a broad interval on human chromosome 7q22-31.1. Using a positional cloning strategy, we have identified the gene (PDS) mutated in Pendred syndrome and found three apparently deleterious mutations, each segregating with the disease in the respective families in which they occur. PDS produces a transcript of approximately 5 kb that was found to be expressed at significant levels only in the thyroid. The predicted protein, pendrin, is closely related to a number of known sulphate transporters. These studies provide compelling evidence that defects in pendrin cause Pendred syndrome thereby launching a new area of investigation into thyroid physiology, the pathogenesis of congenital deafness and the role of altered sulphate transport in human disease.
TL;DR: A novel gene, AIRE, encoding for a putative nuclear protein featuring two PHD-type zinc-finger motifs is isolated, suggesting its involvement in transcriptional regulation in APECED, suggesting the molecular basis of autoimmunity.
Abstract: Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is the only described systemic autoimmune disease with established monogenic background, and the first autoimmune disorder localized outside the major histocompatibility complex (MHC) region. The primary biochemical defect in APECED is unknown. We have isolated a novel gene, AIRE, encoding for a putative nuclear protein featuring two PHD-type zinc-finger motifs, suggesting its involvement in transcriptional regulation. Five mutations in AIRE are reported in individuals with this disorder. This is the first report of a single-gene defect causing a systemic human autoimmune disease, providing a tool for exploring the molecular basis of autoimmunity.
TL;DR: It is likely that this autosomal recessive mutation is the cause of the pancreatic agenesis phenotype in this patient, and IPF1 appears to be a critical regulator of pancreas development in humans as well as mice.
Abstract: The homeodomain protein IPF1 (also known as IDX1, STF1 and PDX1; see Methods) is critical for development of the pancreas in mice and is a key factor for the regulation of the insulin gene in the beta-cells of the endocrine pancreas. Targeted disruption of the Ipf1 gene encoding IPF1 in transgenic mice results in a failure of the pancreas to develop (pancreatic agenesis). Here, we report the identification of a single nucleotide deletion within codon 63 of the human IPF1 gene (13q12.1) in a patient with pancreatic agenesis. The patient is homozygous for the point deletion, whereas both parents are heterozygotes for the same mutation. The deletion was not found in 184 chromosomes from normal individuals, indicating that the mutation is unlikely to be a rare polymorphism. The point deletion causes a frame shift at the C-terminal border of the transactivation domain of IPF1 resulting in the translation of 59 novel codons before termination, aminoproximal to the homeodomain essential for DNA binding. Expression of mutant IPF1 in Cos-1 cells confirms the expression of a prematurely terminated truncated protein of 16 kD. Thus, the affected patient should have no functional IPF1 protein. Given the essential role of IPF1 in pancreas development, it is likely that this autosomal recessive mutation is the cause of the pancreatic agenesis phenotype in this patient. Thus, IPF1 appears to be a critical regulator of pancreas development in humans as well as mice.
TL;DR: It is reported here that in VDR null mutant mice, no defects in development and growth were observed before weaning, irrespective of reduced expression of vitamin D target genes, which establishes a critical role for VDR in growth, bone formation and female reproduction in the post-weaning stage.
Abstract: 1 alpha,25-Dihydroxyvitamin D3[1 alpha,25(OH)2D3], an active form of vitamin D, has roles in many biological phenomena such as calcium homeostasis and bone formation, which are thought to be mediated by the 1 alpha,25(OH)2D3 receptor (VDR), a member of the nuclear hormone receptor superfamily. However, the molecular basis for the actions of 1 alpha,25(OH)2D3 in bone formation, its role during development and VDR genetic polymorphisms for predicting bone mineral density are uncertain. To investigate the functional role of VDR, we generated mice deficient in VDR by gene targeting. We report here that in VDR null mutant mice, no defects in development and growth were observed before weaning, irrespective of reduced expression of vitamin D target genes. After weaning, however, mutants failed to thrive, with appearance of alopoecia, hypocalcaemia and infertility, and bone formation was severely impaired as a typical feature of vitamin D-dependent rickets type II (refs 8, 9). Unlike humans with this disease, most of the null mutant mice died within 15 weeks after birth, and uterine hypoplasia with impaired folliculogenesis was found in female reproductive organs. These defects, such as alopoecia and uterine hypoplasia, were not observed in vitamin D-deficient animals. The findings establish a critical role for VDR in growth, bone formation and female reproduction in the post-weaning stage.
TL;DR: It is concluded that AGS is caused by haploinsufficiency of JAG1, the human homologue of rat Jagged1, which encodes a ligand for the Notch receptor, an attractive candidate gene for a developmental disorder in humans.
Abstract: Alagille syndrome (AGS) is an autosomal-dominant disorder characterized by intrahepatic cholestasis and abnormalities of heart, eye and vertebrae, as well as a characteristic facial appearance. Identification of rare AGS patients with cytogenetic deletions has allowed mapping of the gene of 20p12. We have generated a cloned contig of the critical region and used fluorescent in situ hybridization on cells from patients with submicroscopic deletions to narrow the candidate region to only 250 kb. Within this region we identified JAG1, the human homologue of rat Jagged1, which encodes a ligand for the Notch receptor. Cell-cell Jagged/Notch interactions are known to be critical for determination of cell fates in early development, making this an attractive candidate gene for a developmental disorder in humans. Determining the complete exon-intron structure of JAG1 allowed detailed mutational analysis of DNA samples from non-deletion AGS patients, revealing three frame-shift mutations, two splice donor mutations and one mutation abolishing RNA expression from the altered allele. We conclude that AGS is caused by haploinsufficiency of JAG1.
TL;DR: It is inferred that molecular defects in prohormone conversion may represent a generic mechanism for obesity, common to humans and rodents.
Abstract: Human obesity has an inherited component, but in contrast to rodent obesity, precise genetic defects have yet to be defined. A mutation of carboxypeptidase E (CPE), an enzyme active in the processing and sorting of prohormones, causes obesity in the fat/fat mouse. We have previously described a women with extreme childhood obesity (Fig. 1), abnormal glucose homeostasis, hypogonadotrophic hypogonadism, hypocortisolism and elevated plasma proinsulin and pro-opiomelanocortin (POMC) concentrations but a very low insulin level, suggestive of a defective prohormone processing by the endopeptidase, prohormone convertase 1 (PC1; ref. 4). We now report this proband to be a compound heterozygote for mutations in PC1. Gly-->Arg483 prevents processing of proPC1 and leads to its retention in the endoplasmic reticulum (ER). A-->C+4 of the intro-5 donor splice site causes skipping of exon 5 leading to loss of 26 residues, a frameshift and creation of a premature stop codon within the catalytic domain. PC1 acts proximally to CPE in the pathway of post-translational processing of prohormones and neuropeptides. In view of the similarity between the proband and the fat/fat mouse phenotype, we infer that molecular defects in prohormone conversion may represent a generic mechanism for obesity, common to humans and rodents.
TL;DR: It is concluded that TBX5 is critical for limb and heart development and suggest that haploinsufficiency ofTBX5 causes Holt-Oram syndrome.
Abstract: Holt-Oram syndrome is characterized by upper limb malformations and cardiac septation defects. Here, we demonstrate that mutations in the human TBX5 gene underlie this disorder. TBX5 was cloned from the disease locus on human chromosome 12q24.1 and identified as a member of the T-box transcription factor family. A nonsense mutation in TBX5 causes Holt-Oram syndrome in affected members of one family; a TBX5 missense mutation was identified in affected members of another. We conclude that TBX5 is critical for limb and heart development and suggest that haploinsufficiency of TBX5 causes Holt-Oram syndrome.
TL;DR: A marked deficiency of the SMN protein in SMA is shown and the molecular mechanism underlying the pathogenesis of the disease is elucidated by western blot and immunohistochemical analyses using antibodies raised against theSMN protein.
Abstract: Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder characterized by degeneration of motor neurons of the spinal cord. Three different forms of childhood SMA have been recognized on the basis of age at onset and clinical course: Werdnig-Hoffmann disease (type-1), the intermediate form (type-II) and Kugelberg-Welander disease (type-III). A gene termed 'survival of motor neuron' (SMN) has been recognized as the disease-causing gene in SMA. SMN encodes a protein located within a novel nuclear structure and interacts with RNA-binding proteins. To elucidate the molecular mechanism underlying the pathogenesis of the disease, we examined the expression of the SMN gene in both controls and SMA patients by western blot and immunohistochemical analyses using antibodies raised against the SMN protein. The present study shows a marked deficiency of the SMN protein in SMA.
TL;DR: In vitro transcription and translation of hTRT when co-synthesized or mixed with hTR reconstitutes telomerase activity that exhibits enzymatic properties like those of the native enzyme.
Abstract: The maintenance of chromosome termini, or telomeres, requires the action of the enzyme telomerase, as conventional DNA poly-merases cannot fully replicate the ends of linear molecules1–4. Telomerase is expressed and telomere length is maintained in human germ cells and the great majority of primary human tumours5,6. However, telomerase is not detectable in most normal somatic cells; this corresponds to the gradual telomere loss observed with each cell division7–9. It has been proposed that telomere erosion eventually signals entry into senescence or cell crisis and that activation of telomerase is usually required for immortal cell proliferation10. In addition to the human telomerase RNA component (hTR; ref. 11), TP1/TLP1 (refs 12,13), a protein that is homologous to the p80 protein associated with the Tetrahymena enzyme14, has been identified in humans. More recently, the human telomerase reverse transcriptase (hTRT; refs 15, 16), which is homologous to the reverse transcriptase (RT)-like proteins associated with the Euplotes aediculatus (Ea_p123), Saccharomyces cerevisiae (Est2p) and Schizosaccharomyces pombe (SpTrt!) telomerases15,17, has been reported to be a telomerase protein subunit. A catalytic function has been demonstrated for Est2p in the RT-like class but not for p80 or its homologues17,18. We now report that in vitro transcription and translation of hTRT when co-synthesized or mixed with hTR reconstitutes telomerase activity that exhibits enzymatic properties like those of the native enzyme. Single amino-acid changes in conserved telomerase-specific and RT motifs reduce or abolish activity, providing direct evidence that hTRT is the catalytic protein component of telomerase. Normal human diploid cells transiently expressing hTRT possessed telomerase activity, demonstrating that hTRT is the limiting component necessary for restoration of telomerase activity in these cells. The ability to reconstitute telomerase permits further analysis of its biochemical and biological roles in cell aging and carcinogenesis.
TL;DR: The DYT1 gene on human chromosome 9q34 is identified as being responsible for early-onset torsion dystonia, a movement disorder, characterized by twisting muscle contractures, that begins in childhood.
Abstract: Early-onset torsion dystonia is a movement disorder, characterized by twisting muscle contractures, that begins in childhood. Symptoms are believed to result from altered neuronal communication in the basal ganglia. This study identifies the DYT1 gene on human chromosome 9q34 as being responsible for this dominant disease. Almost all cases of early-onset dystonia have a unique 3-bp deletion that appears to have arisen idependently in different ethnic populations. This deletion results in loss of one of a pair of glutamic-acid residues in a conserved region of a novel ATP-binding protein, termed torsinA. This protein has homologues in nematode, rat, mouse and humans, with some resemblance to the family of heat-shock proteins and Clp proteases.
TL;DR: A deficient activity of the iron-sulphur (Fe-S) cluster-containing subunits of mitochondrial respiratory complexes I, II and III in the endomyocardial biopsy of two unrelated FRDA patients was found to be deficient.
Abstract: Friedreich ataxia (FRDA) is a common autosomal recessive degenerative disease (1/50,000 live births) characterized by a progressive gait and limb ataxia with lack of tendon reflexes in the legs, dysarthria and pyramidal weakness of the inferior limbs(1,2). Hypertrophic cardiomyopathy is observed in most FRDA patients. The gene associated with the disease has been mapped to chromosome 9q13 (ref. 3) and encodes a 210-amino-acid protein, frataxin. FRDA is caused primarily by a GAA repeat expansion within the first intron of the frataxin gene, which accounts for 98% of mutant alleles(4). The function of the protein is unknown, but an increased iron content has been reported in hearts of FRDA patients(5) and the mitochondria of yeast strains carrying a deleted frataxin gene counterpart (YFH1), suggesting that frataxin plays a major role in regulating mitochondrial iron transport(6.7). Here, we report a deficient activity of the iron-sulphur (Fe-S) cluster-containing subunits of mitochondrial respiratory complexes I, II and III in the endomyocardial biopsy of two unrelated FRDA patients. Aconitase, an iron-sulphur protein involved in iron homeostasis, was found to be deficient as well. Moreover, disruption of the YFH1 gene resulted in multiple Fe-S-dependent enzyme deficiencies in yeast. The deficiency of Fe-S-dependent enzyme activities in both FRDA patients and yeast should be related to mitochondrial iron accumulation, especially as Fe-S proteins are remarkably sensitive to free radicals(8). Mutated frataxin triggers aconitase and mitochondrial Fe-S respiratory enzyme deficiency in FRDA, which should therefore be regarded as a mitochondrial disorder.
TL;DR: It is shown that during fetal development and childhood, mRNAs for insulin and other islet cell autoantigens are expressed at low levels in the human thymus, and this finding provides a plausible explanation for the dominant protective effect of class III VNTRs, and suggests that diabetes susceptibility and resistance associated with IDDM2 may derive from the VN TR influence on INS transcription in the thymos.
Abstract: Type 1, or insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease associated with loss of tolerance to several pancreatic islet cell molecules, including insulin, glutamic acid decarboxylase (GAD), ICA69 and the tyrosine phosphatase IA-2 (refs 1-3). Among several predisposing loci, IDDM2 maps to the insulin gene (INS) VNTR (variable number of tandem repeats) minisatellite on chromosome 11p15 (refs 4-9). Allelic variation at this VNTR locus correlates with steady-state levels of INS mRNA in pancreas and transfected rodent cell lines, but it is difficult to reconcile the association of lower INS mRNA levels in the pancreas with class III VNTRs that are dominantly protective from IDDM. We show that during fetal development and childhood, mRNAs for insulin and other islet cell autoantigens (GAD, ICA69, IA-2) are expressed at low levels in the human thymus. Critically, we also detect proinsulin and insulin protein. VNTR alleles correlate with differential INS mRNA expression in the thymus where, in contrast to the pancreas, protective class III VNTRs are associated with higher steady-state levels of INS mRNA expression. This finding provides a plausible explanation for the dominant protective effect of class III VNTRs, and suggests that diabetes susceptibility and resistance associated with IDDM2 may derive from the VNTR influence on INS transcription in the thymus. Higher levels of (pro)insulin in the thymus may promote negative selection (deletion) of insulin-specific T-lymphocytes which play a critical role in the pathogenesis of type-1 diabetes.
TL;DR: A new yeast genomic library is constructed and a highly selective two-hybrid procedure adapted for exhaustive screens of the yeast genome is developed, able to characterize new interactions between known splicing factors, identify new yeast splicing Factors, and reveal novel potential functional links between cellular pathways.
Abstract: The genome of the yeast Saccharomyces cerevisiae is now completely sequenced. Despite successful genetic work in recent years, 60% of yeast genes have no assigned function and half of those encode putative proteins without any homology with known proteins. Genetic analyses, such as suppressor or synthetic lethal screens, have suggested many functional links between gene products, some of which have been confirmed by biochemical means. Altogether, these approaches have led to a fairly extensive knowledge of defined biochemical pathways. However, the integration of these pathways against the background of complexity in a living cell remains to be accomplished. The two-hybrid method applied to the yeast genome might allow the characterization to the network of interactions between yeast proteins, leading to a better understanding of cellular functions. Such an analysis has been performed for the bacteriophage T7 genome that encodes 55 proteins and for Drosophila cell cycle regulators. However, the currently available two-hybrid methodology is not suitable for a large-scale project without specific methodological improvements In particular, the exhaustivity and selectivity of the screens must first be greatly improved. We constructed a new yeast genomic library and developed a highly selective two-hybrid procedure adapted for exhaustive screens of the yeast genome. For each bait we selected a limited set of interacting preys that we classified in categories of distinct heuristic values. Taking into account this classification, new baits were chosen among preys and, in turn, used for second-round screens. Repeating this procedure several times led to the characterization of the network of interactions. Using known pre-mRNA splicing factors as initial baits, we were able to characterize new interactions between known splicing factors, identify new yeast splicing factors, including homologues of human SF1 and SAP49, and reveal novel potential functional links between cellular pathways. Using different cellular pathways as anchor points, this novel strategy allows us to envision the building of an interaction map of the yeast proteome. In addition, this two-hybrid strategy could be applied to other genomes and might help to resolve the human protein linkage map.
TL;DR: TRF2 as discussed by the authors is a distant homologue of TRF1 that carries a very similar Myb-related DNA-binding motif and was found to have similar DNA binding activity and domain organization, but its N terminus was basic rather than acidic.
Abstract: Human telomeres are composed of long arrays of TTAGGG repeats that form a nucleoprotein complex required for the protection and replication of chromosome ends. One component of human telomeres is the TTAGGG repeat binding factor 1 (TRF1), a ubiquitously expressed protein, related to the proto-oncogene Myb, that is present at telomeres throughout the cell cycle1–6. Recent evidence has implicated TRF1 in the control of telomere length7. TRF1 is proposed to be an inhibitor of telomerase, acting in cis to limit the elongation of individual chromosome ends. Here we report the cloning of TRF2, a distant homologue of TRF1 that carries a very similar Myb-related DNA-binding motif. Like TRF1, TRF2 was ubiquitously expressed, bound specifically to duplex TTAGGG repeats in vitro and localized to all human telomeres in metaphase chromosomes. TRF2 was shown to have an architecture similar to that of TRF1 in that it carries a C-terminal Myb motif and a large TRF1-related dimerization domain near its N terminus. However, the dimerization domains of TRF1 and TRF2 did not interact, suggesting that these proteins exist predominantly as homodimers. While having similar telomere binding activity and domain organization, TRF2 differed from TRF1 in that its N terminus was basic rather than acidic, and TRF2 was much more conserved than TRF1. The results indicate that the TTAGGG repeat arrays at the ends of human and mouse chromosomes bind to two related proteins. Because TRF1 and TRF2 showed significant differences, we suggest that these factors have distinct functions at telomeres.
TL;DR: Tissue in situ hybridization studies on human embryos from days 26 to 52 of gestation reveal expression of TBXS in heart and limb, consistent with a role in human embryonic development.
Abstract: Holt-Oram syndrome is a developmental disorder affecting the heart and upper limb, the gene for which was mapped to chromosome 12 two years ago. We have now identified a gene for this disorder (HOS1). The gene (TBX5) is a member of the Brachyury (T) family corresponding to the mouse TbxS gene. We have identified six mutations, three in HOS families and three in sporadic HOS cases. Each of the mutations introduces a premature stop codon in the TBXS gene product. Tissue in situ hybridization studies on human embryos from days 26 to 52 of gestation reveal expression of TBXS in heart and limb, consistent with a role in human embryonic development.