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Biomedical subjects

A Bird

Publications and source records attributed to A Bird.

At least 73 records · Page 4Linked to original sources
PubMed1997

Blood transfusion in South Africa.

Sixty years of development have transformed previously small collection centres into major regional transfusion services. These organisations collect and process nearly 900,000 units of blood annually from a donor base of some 500,000 individuals with a male to female ratio of 5:3. Three quarters of the donations are from a regular pool of largely white people. The latter has both a cultural and socio-economic component that needs redress to meet expanding requests. The range of products and quality of newer technologies, including those that are centered on aphereses are commensurate with first world standards. Quality control is universally monitored and registration falls under prevailing legislation. The future of these vitally important services will need to accommodate changing priorities in South Africa. Specific challenges are a greater commitment to primary health care, the rapidly rising incidence of HIV-positivity and centralisation of some facilities including plasma fractionation.

Blood Transfusion↗
PubMed1997

The dual role of mRNA half-lives in the expression of the yeast ALG7 gene.

The yeast ALG7 gene functions by initiating the synthesis of the dolichol-linked oligosaccharide precursor and plays an important role in the control of protein N-glycosylation. The levels of ALG7 multiple transcripts are modulated by the physiological status of the cell and environmental cues, and deregulation of their abundance is deleterious to several cellular functions. Since ALG7 mRNAs are unstable, we investigated the role of these transcripts' half-lives in determining their steady-state levels. Using a temperature-sensitive RNA polymerase II mutant, we demonstrate that increased stability was the primary determinant of higher ALG7 mRNA abundance in response to glucose limitation or treatment with tunicamycin. In contrast, at the G1/G0 transition point, changes in the decay rates were inversely related to ALG7 transcript accumulation: the decreased abundance of ALG7 mRNAs following exit from the mitotic cycle was associated with lengthening of the decay rates, while their increased accumulation after growth stimulation correlated with decreased stability. This suggests that, depending on the circumstance, mRNA half-lives can either directly determine the level of ALG7 transcript accumulation or oppose regulatory changes at other control levels.

Antifungal Agents↗
PubMed1997

A component of the transcriptional repressor MeCP1 shares a motif with DNA methyltransferase and HRX proteins.

Methylation of cytosines within the sequence CpG is essential for mouse development and has been linked to transcriptional suppression in vertebrate systems. Methyl-CpG binding proteins (MeCPs) 1 and 2 bind preferentially to methylated DNA and can inhibit transcription. The gene for MeCP2 has been cloned and a methyl-CpG binding domain (MBD) within it has been defined. A search of DNA sequence databases with the MBD sequence identified a human cDNA with potential to encode an MBD-like region. Sequencing of the complete cDNA revealed that the open reading frame also encodes two cysteine-rich domains that are found in animal DNA methyltransferases (DNMTs) and in the mammalian HRX protein (also known as MLL and All-1). HRX is related to Drosophila trithorax. The protein, known as Protein Containing MBD (PCM1), was expressed in bacteria and shown to bind specifically to methylated DNA. PCM1 also repressed transcription in vitro in a methylation-dependent manner. A polyclonal antibody raised against the protein was able to 'supershift' the native MeCP11 complex from HeLa cells, indicating that PCM1 is a component of mammalian MeCP1.

Amino Acid Sequence↗
PubMed1997

Mosaic methylation of the repeat unit of the human ribosomal RNA genes.

The pattern of methylation in human genes for 18S and 28S ribosomal RNA has been investigated using methylation-sensitive restriction enzymes. We find that the transcribed region of the repeat unit is predominantly unmethylated, in agreement with previous studies. In contrast the non-transcribed spacer, which makes up the majority of the 43 kb repeat unit, is highly methylated in blood cell DNA. The boundaries between methylated and non-methylated domains appear to be relatively sharp, and occur approximately 1.5 kb upstream of the 5' edge of the proximal promoter and approximately 1.0 kb downstream of the 3' end of the transcribed region. A small proportion of all repeat units are methylated throughout the transcribed region, and may represent silent genes. The coincidence between the methylation pattern, the transcription pattern and other features of the repeat unit has implications for our understanding of the mechanism by which patterns of DNA methylation are generated.

Blotting, Southern↗
PubMed1997

Methylation of genomes and genes at the invertebrate-vertebrate boundary.

Patterns of DNA methylation in animal genomes are known to vary from an apparent absence of modified bases, via methylation of a minor fraction of the genome, to genome-wide methylation. Representative genomes from 10 invertebrate phyla comprise predominantly nonmethylated DNA and (usually but not always) a minor fraction of methylated DNA. In contrast, all 27 vertebrate genomes that have been examined display genome-wide methylation. Our studies of chordate genomes suggest that the transition from fractional to global methylation occurred close to the origin of vertebrates, as amphioxus has a typically invertebrate methylation pattern whereas primitive vertebrates (hagfish and lamprey) have patterns that are typical of vertebrates. Surprisingly, methylation of genes preceded this transition, as many invertebrate genes have turned out to be heavily methylated. Methylation does not preferentially affect genes whose expression is highly regulated, as several housekeeping genes are found in the heavily methylated fraction whereas several genes expressed in a tissue-specific manner are in the nonmethylated fraction.

Animals↗
PubMed1997

Hepatitis C virus infection rate in volunteer blood donors from the Western Cape--comparison of screening tests and PCR.

INTRODUCTION: Hepatitis C virus (HCV) antibody seroprevalence studies overestimate the true infection rate. No data exist on the incidence of HCV or its clinical features in blood donors of sub-Saharan Africa. AIMS: To establish the true incidence of HCV infection in volunteer blood donors in the Western Cape, and compare risk factors and clinical and biochemical features of viraemic and non-viraemic subjects. METHODS: All donors attending the Western Province Blood Transfusion Service between December 1992 and August 1994 were screened prospectively for anti-HCV using the Abbott second-generation assay. Positive donors were evaluated clinically and biochemically. Their sera were examined for HCV-RNA by the polymerase chain reaction (PCR). RESULTS: Of 66314 donors screened, 275 (0.41%) were anti-HCV-positive. Of these 13.6% were PCR-positive (0.056% of all donors). PCR-positive patients had more risk factors for HCV acquisition (P < 0.01), symptoms of hepatitis (P = 0.02) and clinical signs of liver disease (P = 0.05) and higher alanine (P < 0.0001) and aspartate aminotransferase levels (P < 0.0001) than PCR-negative donors. However, clinical and biochemical features did not discriminate adequately between PCR-positive and negative donors. Liver biopsies performed in 9 of 13 PCR-positive cases showed mild inflammation, but no cirrhosis.

Blood Donors↗
PubMed1996

Rational modulation of the catalytic activity of A1-1 glutathione S-transferase: evidence for incorporation of an on-face (pi...HO-Ar) hydrogen bond at tyrosine-9.

The alpha-, pi-, and mu-class glutathione S-transferases utilize a hydrogen bond between a conserved tyrosine and glutathione (GSH) to stabilize the nucleophilic thiolate anion, as Tyr-OH...-SG. This hydrogen bond is critical for efficient detoxication catalysis. The detailed structure of this hydrogen bond, however, is controlled by active site features which are not conserved across class boundaries. The alpha-class GST A1-1 has a cluster of aromatic residues on one side of the ring of the catalytic tyrosine, Tyr-9. Also, a hydrophobic Met-16 side chain is packed against the edge of the ring of Tyr-9. Molecular modeling and ab initio calculations suggested that substitution of Phe-220 with tyrosine could generate an aromatic on-face hydrogen bond (pi...HO-Ar) between the ring of Tyr-9 and the hydroxyl group of Tyr-220, and this would lower the pKa of enzyme-bound GSH. Therefore, Phe-220 was replaced by Tyr in the rat A1-1 isozyme. Also, Met-16 was replaced by Thr in order to investigate the effect of a hydrogen bond donor at the Tyr-9 ring edge. UV spectroscopic titration of GST.GSH and steady-state kinetic analysis indicate that substitution of Tyr at Phe-220 results in a decrease of the pKa of the cofactor, whereas substitution of Met-16 with Thr results in an increase of this pKa. Also, the pKa of Tyr-9 in the absence of substrates was determined directly by fluorescence titration. Substitutions F220Y and M16T resulted in a decrease of 0.5 pKa unit and an increase of 0.6 pKa unit, respectively. Together, these results indicate that a weak hydrogen bond between the engineered Tyr-220 side chain and the aromatic ring face of the catalytic Tyr-9 decreases the pKa of GSH and Tyr-9, and this alters the pH dependence of the enzymatic reaction.

Amino Acid Sequence↗
PubMed1996

A longitudinal study of factors predicting change in cognitive test scores over time, in an older hypertensive population.

This study aims to describe factors associated with cognitive decline among 2584 subjects, aged 65-74, who were followed up for 54 months in the Medical Research Council Elderly Hypertension Trial (1982-1989). The subjects completed a cognitive test, the Paired Associate Learning Test (PALT), five times over this period. Decline on the PALT was associated with advanced age, male sex, rural residence, depression and low intelligence. These effects were modified by gender and level of pre-morbid intelligence. Advanced age, rural residence and number of cigarettes smoked daily were only associated with PALT decline among women of below median intelligence. The association between depression and PALT decline was only apparent in women of below median intelligence and men of above median intelligence. While these findings are consistent with other research into cognitive decline, they differ in some ways from reported risk factors for dementia, suggesting aetiological separateness. That women were more vulnerable than men to the effects of age and smoking raises the question of the impact on cognition of accelerated atherosclerosis after the menopause.

Aged↗
PubMed1996

The methyl-CpG binding protein MeCP2 is essential for embryonic development in the mouse.

Vertebrate genomes are heavily methylated at cytosines in the sequence CpG. The biological role of this modification is probably mediated by DNA binding proteins that are either attracted to or repelled by methyl-CpG. MeCP2 is an abundant chromosomal protein that binds specifically to methylated DNA in vitro, and depends upon methyl-CpG for its chromosomal distribution in vivo. To assess the functional significance of MeCP2, the X-linked gene was mutated in male mouse embryonic stem (ES) cells using a promoterless gene-targeting construct containing a lacZ reporter gene. Mutant ES cells lacking MeCP2 grew with the same vigour as the parental line and were capable of considerable differentiation. Chimaeric embryos derived from several independent mutant lines, however, exhibited developmental defects whose severity was positively correlated with the contribution of mutant cells. The results demonstrate that MeCP2, like DNA methyltransferase, is dispensable in stem cells, but essential for embryonic development.

Animals↗
PubMed1996

A gene (RPGR) with homology to the RCC1 guanine nucleotide exchange factor is mutated in X-linked retinitis pigmentosa (RP3).

X-linked retinitis pigmentosa (xlRP) is a severe progressive retinal degeneration which affects about 1 in 25,000 of the population. The most common form of xlRP, RP3, has been localised to the interval between CYBB and OTC in Xp21.1 by linkage analysis and deletion mapping. Identification of microdeletions within this region has now led to the positional cloning of a gene, RPGR, that spans 60 kg of genomic DNA and is ubiquitously expressed. The predicted 90 kD protein contains in its N-terminal half a tandem repeat structure highly similar to RCC1 (regulator of chromosome condensation), suggesting an interaction with a small GTPase. The C-terminal half contains a domain, rich in acidic residues, and ends in a potential isoprenylation anchorage site. The two intragenic deletions, two nonsense and three missense mutations within conserved domains provide evidence that RPGR (retinitis pigmentosa GTPase regulator) is the RP3 gene.

Amino Acid Sequence↗
PubMed1996

DNA methylation specifies chromosomal localization of MeCP2.

MeCP2 is a chromosomal protein that is concentrated in the centromeric heterochromatin of mouse cells. In vitro, the protein binds preferentially to DNA containing a single symmetrically methylated CpG. To find out whether the heterochromatic localization of MeCP2 depended on DNA methylation, we transiently expressed MeCP2-LacZ fusion proteins in cultured cells. Intact protein was targeted to heterochromatin in wild-type cells but was inefficiently localized in mutant cells with low levels of genomic DNA methylation. Deletions within MeCP2 showed that localization to heterochromatin required the 85-amino-acid methyl-CpG binding domain but not the remainder of the protein. Thus MeCP2 is a methyl-CpG-binding protein in vivo and is likely to be a major mediator of downstream consequences of DNA methylation.

Amino Acid Sequence↗
PubMed1996

The necessity for T-cryptantigen activation screening in babies with necrotising enterocolitis.

OBJECTIVE: To determine the prevalence of T-cryptantigen activation (TCA) and its predictive value for severity of necrotising enterocolitis (NEC) in babies. STUDY DESIGN: Prospective descriptive. STUDY POPULATION: Thirty-four babies with NEC were prospectively screened for TCA at Tygerberg Hospital over a 6-month period. TCA screening was done by testing for red blood cell agglutination by the common peanut lectin, Arachis hypogea. Once TCA was confirmed, only washed red cells were administered to the babies and plasma-containing blood products were avoided. NEC was divided into suspected NEC (stage 1), classic NEC (stage 2) and fulminant NEC (stage 3). MAIN OUTCOME MEASURES: Prevalence of TCA in babies with various stages of NEC; the association between TCA and bowel necrosis, need for surgery and mortality. RESULTS: TCA was positive in 8 (24%) of the babies in this study. Six babies (18%) had stage 1 NEC, 10 (29%) had stage 2 NEC and 18 (53%) had fulminating or stage 3 NEC. All 18 babies with stage 3 NEC required surgery and TCA was present in 8 (47%) of them. Twelve babies (35%) died, 3 with TCA and 9 with no TCA. Babies with TCA had portal venous gas on abdominal radiographs (P = 0.037) and stage 3 NEC (P = 0.003) more often than babies with no TCA. CONCLUSIONS: A strong association was noted between TCA and the fulminant form of NEC with bowel necrosis. TCA is a baby with NEC should alert the surgeon to the possibility of severe disease and the need to avoid plasma-containing blood products. Blood banks are urged to introduce routine screening for TCA in all babies with NEC.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed1995

Binding of histone H1 to DNA is indifferent to methylation at CpG sequences.

The possibility that histone H1 binds preferentially to DNA containing 5-methylcytosine in the dinucleotide CpG is appealing, as it could help to explain the repressive effects of methylation on gene activity. In this study, the affinity of purified H1 for methylated and non-methylated DNA sequences has been tested using both naked DNA and chromatin. Based on a variety of assays (bandshifts, filter-binding assays, Southwestern blots, and nuclease sensitivity assays), we conclude that H1 has no significant preference for binding to naked methylated DNA. Similarly, H1 showed the same affinities for methylated and non-methylated DNA when assembled into chromatin in a Xenopus oocyte extract. Thus potential cooperative interaction of H1 with polynucleosomal complexes is not enhanced by the presence of DNA methylation.

Animals↗
PubMed1995

Transcriptional noise and the evolution of gene number.

Several proposals are made to explain the apparent increase in complexity of certain lineages during evolution. The proposals (not made in this order) are: (1) that gene number is a valid measure of biological complexity; (2) that gene number has not increased continuously during evolution, but has risen in discrete steps; (3) that two of the biggest steps occurred at the transition from prokaryotes to eukaryotes and the transition from invertebrates to vertebrates; (4) that these steps were made possible by 'systemic' changes in the way that genetic information is managed in the genome; (5) that the ability to silence inappropriate promoters is the primary limitation on gene number; (6) that the invention of nucleosomes (and perhaps the nuclear membrane) facilitated the evolution of eukaryotes from prokaryotic ancestors; (7) that the spread of low density methylation throughout the genome facilitated the evolution of vertebrates from invertebrate ancestors.

Animals↗
PubMed1995

Cytotoxic interactions of tumor necrosis factor, melphalan and 41.8 degrees C hyperthermia.

Experience with limb perfusion-hyperthermia, TNF, and L-PAM suggests dramatic clinical responses in sarcoma and malignant melanoma. To extrapolate these results to clinical 41.8 degrees C whole-body hyperthermia (WBH) and systemic therapy, we studied the cytotoxic interactions of TNF, L-PAM and hyperthermia in L929 cells. The optimal sequence was TNF preceding 41.8 degrees C hyperthermia by 48 h, and L-PAM given simultaneously with heat. Trimodality synergism between TNF, hyperthermia and L-PAM was demonstrated. Non-cytotoxic doses of TNF had a super-additive interaction with L-PAM/heat. Conversely, non-cytotoxic doses of L-PAM had super-additive interactions with TNF followed by hyperthermia. Relative to therapeutic index, we studied WBH, L-PAM and TNF in non-tumor bearing mice. The optimal trimodality sequence did not result in increased normal tissue toxicity compared to L-PAM alone. The concentrations and sequencing of TNF and L-PAM studied are consistent with clinical application to WBH.

Animals↗
PubMed1995

Expression of the first N-glycosylation gene in the dolichol pathway, ALG7, is regulated at two major control points in the G1 phase of the Saccharomyces cerevisiae cell cycle.

The Saccharomyces cerevisiae ALG7 gene, which functions by initiating the dolichol pathway of protein N-glycosylation, displays properties of an early growth-response gene. To initiate studies of the involvement of ALG7 in cellular proliferation, we have now more precisely analyzed ALG7 expression in the G1 phase of cell cycle. We show that the rapid rate of ALG7 mRNA accumulation following growth stimulation was attenuated soon thereafter and that ALG7 growth induction occurred irrespective of alpha-factor. ALG7 growth induction was observed in mutants conditionally defective for reentry into the cell cycle from the stationary phase, indicating that the induction occurred prior to the performance of START. In addition, the steady-state levels of ALG7 mRNAs declined four-fold in response to START-I cell division arrest brought about by alpha-factor treatment later in G1. Importantly, deregulated expression of ALG7 resulted in an aberrant alpha-factor response. Our data not only indicate that ALG7 expression is regulated at two critical control points in G1 that determine the proliferative potential of cells, but also provide a link between ALG7 and START.

Cell Cycle↗