Search PubMed⌕ Search

Biomedical subjects

A Bird

Publications and source records attributed to A Bird.

At least 55 records · Page 3Linked to original sources
PubMed1999

Genomic structure and chromosomal mapping of the murine and human Mbd1, Mbd2, Mbd3, and Mbd4 genes.

DNA methylation is essential for murine development and is implicated in the control of gene expression. MeCP2, MBD1, MBD2, MBD3, and MBD4 comprise a family of mammalian, nuclear proteins related by the presence in each of an amino acid motif called the methyl-CpG binding domain (MBD). Each of these proteins, with the exception of MBD3, is capable of binding specifically to methylated DNA. MeCP2, MBD1 and MBD2 can also repress transcription. We describe the genomic structure and chromosomal localization of the human and murine Mbd1, Mbd2, Mbd3, and Mbd4 genes. We find that the highly similar MBD2 and MBD3 proteins are encoded by genes that map to different chromosomes in humans and mice but show a similar genomic structure. The Mbd1 and Mbd2 genes, in contrast, map together to murine and human Chromosomes (Chrs)18. The Mbd3 and Mbd4 genes map to murine Chrs 10 and 6, respectively, while the human MBD3 and MBD4 genes map to Chrs 19 and 3, respectively.

Animals↗
PubMed1999

DNA methylation and chromatin modification.

DNA methylation and chromatin modification are two global mechanisms that regulate gene expression. Recent studies provide insight into the mechanism of transcriptional silencing by a methyl-CpG binding protein, MeCP2. MeCP2 is shown to interact with the Sin3/histone deacetylase co-repressor complex. Thus, this interaction can provide a mechanistic explanation for the long-known relationship between DNA methylation and chromatin structure. Moreover, several studies have shown that inhibition of histone deacetylases by specific inhibitors can reactivate endogenous genes or reporter constructs previously silenced by DNA methylation. Taken together, the data strongly suggest that DNA methylation can pattern chromatin modification.

Acetylation↗
PubMed1999

Changes in Bruch's membrane and related structures with age.

Age-related macular disease is a major and growing public health burden in developed Caucasian societies, accounting for about 50% of blind registration. Evidence exists that this is an emerging problem in Eastern Asia, although the phenotype appears to differ from that seen in Western society. It is likely that several genes are involved, and that the genes or allelic variants conferring are common. Environment plays a major role in its pathogenesis, and it is believed that genetic susceptibility becomes apparent only if there are sufficient environmental pressures. There is no therapy currently available that will have an impact on the prevalence of blindness from age-related macular disease. It has been shown that visual loss occurs as a reaction to ageing changes in Bruch's membrane, which is interposed between the choriocapillaris and the retinal pigment epithelium. The age changes in all three structures have been partly characterised, and as a consequence, multiple putative pathogenic mechanisms have been proposed. Cross-sectional studies of populations with different genetic background and life styles would serve to prove the importance of inheritance and environment. Molecular genetic analysis of blood from affected sibling pairs from these sources may indicate the relevant genes, the prevalence of which may differ in different communities. Enquiries as to life styles may determine important environmental influences. Examination of donor eyes from these communities may reveal distinctive features that may reflect the variation in genetic predisposition and environmental pressures. It is hoped that the findings from such studies will lead to novel and potentially successful management strategies.

Aging↗
PubMed1999

MBD2 is a transcriptional repressor belonging to the MeCP1 histone deacetylase complex.

Mammalian DNA is methylated at many CpG dinucleotides. The biological consequences of methylation are mediated by a family of methyl-CpG binding proteins. The best characterized family member is MeCP2, a transcriptional repressor that recruits histone deacetylases. Our report concerns MBD2, which can bind methylated DNA in vivo and in vitro and has been reported to actively demethylate DNA (ref. 8). As DNA methylation causes gene silencing, the MBD2 demethylase is a candidate transcriptional activator. Using specific antibodies, however, we find here that MBD2 in HeLa cells is associated with histone deacetylase (HDAC) in the MeCP1 repressor complex. An affinity-purified HDAC1 corepressor complex also contains MBD2, suggesting that MeCP1 corresponds to a fraction of this complex. Exogenous MBD2 represses transcription in a transient assay, and repression can be relieved by the deacetylase inhibitor trichostatin A (TSA; ref. 12). In our hands, MBD2 does not demethylate DNA. Our data suggest that HeLa cells, which lack the known methylation-dependent repressor MeCP2, use an alternative pathway involving MBD2 to silence methylated genes.

Amino Acid Sequence↗
PubMed1999

Mutations in the RP1 gene causing autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration that affects approximately 1 in 3500 people worldwide. Recently we identified the gene responsible for the RP1 form of autosomal dominant retinitis pigmentosa (adRP) at 8q11-12 and found two different nonsense mutations in three families previously mapped to 8q. The RP1 gene is an unusually large protein, 2156 amino acids in length, but is comprised of four exons only. To determine the frequency and range of mutations in RP1 we screened probands from 56 large adRP families for mutations in the entire gene. After preliminary results indicated that mutations seem to cluster in a 442 nucleotide segment of exon 4, an additional 194 probands with adRP and 409 probands with other degenerative retinal diseases were tested for mutations in this region alone. We identified eight different disease-causing mutations in 17 of the 250 adRP probands tested. All of these mutations are either nonsense or frameshift mutations and lead to a severely truncated protein. Two of the eight different mutations, Arg677X and a 5 bp deletion of nucleotides 2280-2284, were reported previously, while the remaining six mutations are novel. We also identified two rare missense changes in two other families, one new polymorphic amino acid substitution, one silent substitution and a rare variant in the 5'-untranslated region that is not associated with disease. Based on this study, mutations in RP1 appear to cause at least 7% (17/250) of adRP. The 5 bp deletion of nucleotides 2280-2284 and the Arg677X nonsense mutation account for 59% (10/17) of these mutations. Further studies will determine whether missense changes in the RP1 gene are associated with disease, whether mutations in other regions of RP1 can cause forms of retinal disease other than adRP and whether the background variation in either the mutated or wild-type RP1 allele plays a role in the disease phenotype.

Adult↗
PubMed1998

Transcriptional repression by the methyl-CpG-binding protein MeCP2 involves a histone deacetylase complex.

Cytosine residues in the sequence 5'CpG (cytosine-guanine) are often postsynthetically methylated in animal genomes. CpG methylation is involved in long-term silencing of certain genes during mammalian development and in repression of viral genomes. The methyl-CpG-binding proteins MeCP1 and MeCP2 interact specifically with methylated DNA and mediate transcriptional repression. Here we study the mechanism of repression by MeCP2, an abundant nuclear protein that is essential for mouse embryogenesis. MeCP2 binds tightly to chromosomes in a methylation-dependent manner. It contains a transcriptional-repression domain (TRD) that can function at a distance in vitro and in vivo. We show that a region of MeCP2 that localizes with the TRD associates with a corepressor complex containing the transcriptional repressor mSin3A and histone deacetylases. Transcriptional repression in vivo is relieved by the deacetylase inhibitor trichostatin A, indicating that deacetylation of histones (and/or of other proteins) is an essential component of this repression mechanism. The data suggest that two global mechanisms of gene regulation, DNA methylation and histone deacetylation, can be linked by MeCP2.

Acetylation↗
PubMed1998

Initiation of DNA replication at CpG islands in mammalian chromosomes.

CpG islands are G+C-rich regions approximately 1 kb long that are free of methylation and contain the promoters of many mammalian genes. Analysis of in vivo replication intermediates at three hamster genes and one human gene showed that the CpG island regions, but not their flanks, were present in very short nascent strands, suggesting that they are replication origins (ORIs). CpG island-like fragments were enriched in a population of short nascent strands from human erythroleukaemic cells, suggesting that islands constitute a significant fraction of endogenous ORIs. Correspondingly, bulk CpG islands were found to replicate coordinately early in S phase. Our results imply that CpG islands are initiation sites for both transcription and DNA replication, and may represent genomic footprints of replication initiation.

Adenine Phosphoribosyltransferase↗
PubMed1998

Gene number in an invertebrate chordate, Ciona intestinalis.

Gene number can be considered a pragmatic measure of biological complexity, but reliable data is scarce. Estimates for vertebrates are 50-100,000 genes per haploid genome, whereas invertebrate estimates fall below 25,000. We wished to test the hypothesis that the origin of vertebrates coincided with extensive gene creation. A prediction is that gene number will differ sharply between invertebrate and vertebrate members of the chordate phylum. A gene number estimation method requiring limited sequence sampling of genomic DNA was developed and validated by using data for Caenorhabditis elegans. Using the method, we estimated that the invertebrate chordate Ciona intestinalis has 15,500 protein-coding genes (+/-3,700). This number is significantly lower than gene numbers of vertebrate chordates, but similar to those of invertebrates in distantly related phyla. The data indicate that evolution of vertebrates was accompanied by a dramatic increase in protein-coding capacity of the genome.

Animals↗
PubMed1998

Gene silencing by methyl-CpG-binding proteins.

An important consequence of CpG methylation is the local silencing of gene expression. In part this can be mediated by direct interference of methylation with the binding of transcription factors. The major component of silencing, however, appears to be the binding of repressors that have an affinity for methyl-CpG. We have studied two proteins that bind to methylated DNA, methyl-CpG-binding protein 1 (MeCP1) and MeCP2. MeCP2 is a relatively abundant chromosomal protein whose localization in the nucleus is primarily dependent on CpG methylation. We find that MeCP2 is a potent transcriptional repressor with a genome-wide distribution. MeCP1 requires multiple methylated CpGs for binding and has previously been implicated as a methyl-CpG-dependent transcriptional repressor. Recent cloning of a candidate gene for a component of MeCP1 may provide clues to its mechanism of action.

Animals↗
PubMed1998

Factor concentrates for haemophilia in the developing world.

The success in the management of haemophilia in the last two decades has been predominantly due to the availability of sufficient quantities of safe factor concentrates. Unfortunately, the prohibitive cost of these products has prevented this benefit from being available to the vast majority (approximately 80%) of haemophiliacs living in the developing world. A few developing countries have established facilities for the production of low- to intermediate-purity factor concentrates locally. The infrastructure required to achieve this can be very basic. The experience in South Africa, Thailand, Cuba and Brazil, described herein, shows that this approach provides factor concentrates which are very economical in comparison with more purified commercial products. This has had a major impact on the quality of haemophilia care in these countries. Wide availability of low-cost factor concentrates has made these products accessible to a large number of haemophiliacs and even made home therapy possible. The effort to provide these products results in improvement of the blood transfusion services. This, in turn, contributes to better facilities for patients with other transfusion-dependent diseases and society in general. Installation of small plasma fractionation plants is also a viable option. This not only allows processing of large pools of plasma for greater quantities of factor concentrates but also provides albumin and immunoglobulin. The revenue generated from the sale of the other products has been used to improve and subsidize haemophilia care. It is concluded that local production of intermediate purity factor concentrates in developing countries is absolutely necessary. A well organized transfusion service is required to collect adequate quantities of plasma for fractionation.

Blood Coagulation Factors↗
PubMed1998

Identification and characterization of a family of mammalian methyl-CpG binding proteins.

Methylation at the DNA sequence 5'-CpG is required for mouse development. MeCP2 and MBD1 (formerly PCM1) are two known proteins that bind specifically to methylated DNA via a related amino acid motif and that can repress transcription. We describe here three novel human and mouse proteins (MBD2, MBD3, and MBD4) that contain the methyl-CpG binding domain. MBD2 and MBD4 bind specifically to methylated DNA in vitro. Expression of MBD2 and MBD4 tagged with green fluorescent protein in mouse cells shows that both proteins colocalize with foci of heavily methylated satellite DNA. Localization is disrupted in cells that have greatly reduced levels of CpG methylation. MBD3 does not bind methylated DNA in vivo or in vitro. MBD1, MBD2, MBD3, and MBD4 are expressed in somatic tissues, but MBD1 and MBD2 expression is reduced or absent in embryonic stem cells which are known to be deficient in MeCP1 activity. The data demonstrate that MBD2 and MBD4 bind specifically to methyl-CpG in vitro and in vivo and are therefore likely to be mediators of the biological consequences of the methylation signal.

Amino Acid Sequence↗
PubMed1998

An alternative promoter in the mouse major histocompatibility complex class II I-Abeta gene: implications for the origin of CpG islands.

Nonmethylated CpG islands are generally located at the 5' ends of genes, but a CpG island in the mouse major histocompatibility complex class II I-Abeta gene is remote from the promoter and covers exon 2. We have found that this CpG island includes a novel intronic promoter that is active in embryonic and germ cells. The resulting transcript potentially encodes a severely truncated protein which would lack the signal peptide and external beta1 domains. The functional significance of the internal CpG island may be to facilitate gene conversion, thereby sustaining the high level of polymorphism seen at exon 2. Deletions of the I-Abeta CpG island promoter reduce transcription and frequently lead to methylation of the CpG island in a transgenic mouse assay. These and other results support the idea that all CpG islands arise at promoters that are active in early embryonic cells.

Animals↗
PubMed1997

Deregulation of the first N-glycosylation gene, ALG7, perturbs the expression of G1 cyclins and cell cycle arrest in Saccharomyces cerevisiae.

The evolutionarily conserved ALG7 gene encodes the dolichol-P-dependent N-acetylglucosamine-1-P transferase (GPT) and functions by initiating the dolichol pathway of protein N-glycosylation. In Saccharomyces cerevisiae, ALG7 has been shown to play a role in cell proliferation. The yeast alpha-factor-induced cell cycle arrest in G1 occurs, in part, by downregulation of CLN1 and CLN2. The function of ALG7 in G1 arrest was examined in alg7 mutants containing diminished GPT activity. In wild type, CLN1 and CLN2 mRNAs were rapidly downregulated, while in alg7 mutants, these transcripts were only transiently repressed before becoming greatly augmented. Analyses of DNA contents and budding indices showed that alg7 mutants resumed cycling when wild type cells remained arrested. Thus, deregulation of ALG7 interferes with cell cycle arrest by preventing a sustained downregulation of CLN1 and CLN2 mRNAs. These results provide a molecular insight into the role of ALG7, and protein N-glycosylation in general, in proliferation.

Cell Cycle↗
PubMed1997

MeCP2 is a transcriptional repressor with abundant binding sites in genomic chromatin.

MeCP2 is an abundant mammalian protein that binds to methylated CpG. We have found that native and recombinant MeCP2 repress transcription in vitro from methylated promoters but do not repress nonmethylated promoters. Repression is nonlinearly dependent on the local density of methylation, becoming significant at the density found in bulk vertebrate genomic DNA. Transient transfection using fusions with the GAL4 DNA binding domain identified a region of MeCP2 that is capable of long-range repression in vivo. Moreover, MeCP2 is able to displace histone H1 from preassembled chromatin that contains methyl-CpG. These properties, together with the abundance of MeCP2 and the high frequency of its 2 bp binding site, suggest a role as a global transcriptional repressor in vertebrate genomes.

Animals↗