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Biomedical subjects

G Meredith

Publications and source records attributed to G Meredith.

16 recordsLinked to original sources
PubMed2005

Glucagon-like peptide-1 enhances production of insulin in insulin-producing cells derived from mouse embryonic stem cells.

Embryonic stem cells (ESCs) can be differentiated into insulin-producing cells by a five-stage procedure involving altering culture conditions and addition of nicotinamide. The amounts of insulin in these cells are lower than those found in pancreatic beta cells. Glucagon-like peptide-1 (GLP-1) induces the differentiation of beta cells from ductal progenitor cells. We examined the possibility of GLP-1, and its long-acting agonist exendin-4, enhancing the differentiation of insulin-producing cells from mouse ESCs (mESCs). A five-stage culturing strategy starting with embryoid bodies (EBs) was used in this study. mRNA for pancreatic duodenal homeobox gene 1 (PDX-1) and neurogenic differentiation (NeuroD) was detected from stage 1, hepatocyte nuclear factor 3 beta (HNF3beta) and insulin 2 from stage 2, Ngn3 and glucose transporter 2 (GLUT2) from stage 3, and insulin 1 and other beta-cell markers, at stages 4-5. Cells at stage 5 secreted C-peptide, being 0.68 +/- 0.01 pmol/10(6) cells per 2 days, and had an immunoreactive insulin content of 13.5 +/- 0.7 pmol/10(6) cells. Addition of GLP-1 (100 nM) and nicotinamide (10 mM) at stage 5 resulted in a 50% and 48% increase in insulin content and C-peptide secretion respectively compared with nicotinamide alone. Glucose-induced insulin secretion was enhanced 4-fold by addition of both growth factors. The GLP-1 receptor was present at all five stages of the culture. Addition of exendin-4 to cells at stage 2 resulted in a 4.9-fold increase in expression of the gene for insulin 1 and a 2-fold increase in insulin content compared with the effect of nicotinamide alone at stage 5. It is concluded that both GLP-1 and exendin-4 enhance the level of expression of insulin in glucose-responsive insulin-producing cells derived from the R1 mESC line.

Animals↗
PubMed2004

Dwell time and functional failure in percutaneous endoscopic gastrostomy tubes: a prospective randomized-controlled comparison between silicon polymer and polyurethane percutaneous endoscopic gastrostomy tubes.

BACKGROUND: Silicone percutaneous endoscopic gastros-tomy (PEG) tubes are associated with more short-term complications and possibly fail sooner than those made of polyurethane. Understanding the deterioration and long-term complications leading to tube failure has important clinical and cost implications. AIM: To compare dwell time and patterns of failure ofsilicone polymer and polyurethane PEG tubes. METHODS: Participants randomized to receive a siliconepolymer (n = 76) or polyurethane (n = 62) PEG werevisited monthly for 540 days, until death or tube removal. Tube and exit site characteristics and reasons for removal were recorded. RESULTS: Tube failure occurred in 25% of silicone PEGs and 12.9% of polyurethane PEGs. Mean tube survival for silicone PEGs was 377.2 days (CI: 326-428) and for polyurethane 436.8 days (CI: 383-490; P = 0.13). A greater proportion of silicone PEGs developed intralumenal colonization and altered tube integrity than polyurethane (P < 0.001). Silicone PEGs blocked more frequently (P < 0.005) and were removed because of irreversible blockage more often than polyurethane PEGs (P < 0.05). Silicone PEGs with reversible blockage and tube integrity changes had a significantly greater probability of failure than silicone tubes without these changes (P < 0.005 and P < 0.05, respectively). CONCLUSIONS: Observations over time indicate that sili-cone PEGs are more susceptible than polyurethane PEGs to tube deterioration, resulting in substantially increased management demands to sustain patients' feeding and medication schedules.

Adult↗
PubMed1998

Structure of wild-type yeast RNA polymerase II and location of Rpb4 and Rpb7.

The three-dimensional structure of wild-type yeast RNA polymerase II has been determined at a nominal resolution of 24 A. A difference map between this structure and that of the polymerase lacking subunits Rpb4 and Rpb7 showed these two subunits forming part of the floor of the DNA-binding (active center) cleft, and revealed a slight inward movement of the protein domain surrounding the cleft. Surface plasmon resonance measurements showed that Rpb4 and Rpb7 stabilize a minimal pre-initiation complex containing promoter DNA, TATA box-binding protein (TBP), transcription factor TFIIB and the polymerase. These findings suggest that Rpb4 and Rpb7 play a role in coupling the entry of DNA into the active center cleft to closure of the cleft. Such a role can explain why these subunits are necessary for promoter-specific transcription in vitro and for a normal stress response in vivo.

Binding Sites↗
PubMed1990

Sequence of the cDNA and 5'-flanking region for human acid alpha-glucosidase, detection of an intron in the 5' untranslated leader sequence, definition of 18-bp polymorphisms, and differences with previous cDNA and amino acid sequences.

Acid maltase or acid alpha-glucosidase (GAA) is a lysosomal enzyme that hydrolyzes glycogen to glucose and is deficient in glycogen storage disease type II. Previously, we isolated a partial cDNA (1.9 kb) for human GAA; we have now used this cDNA to isolate and determine sequence in longer cDNAs from four additional independent cDNA libraries. Primer extension studies indicated that the mRNA extended approximately 200 bp 5' of the cDNA sequence obtained. Therefore, we isolated a genomic fragment containing 5' cDNA sequences that overlapped the previous cDNA sequence and extended an additional 24 bp to an initiation codon within a Kozak consensus sequence. The sequence of the genomic clone revealed an intron-exon junction 32 bp 5' to the ATG, indicating that the 5' leader sequence was interrupted by an intron. The remaining 186 bp of 5' untranslated sequence was identified approximately 3 kb upstream. The promoter region upstream from the start site of transcription was GC rich and contained areas of homology to Sp1 binding sites but no identifiable CAAT or TATA box. The combined data gave a nucleotide sequence of 2,856 bp for the coding region from the ATG to a stop codon, predicting a protein of 952 amino acids. The 3' untranslated region contained 555 bp with a polyadenylation signal at 3,385 bp followed by 16 bp prior to a poly(A) tail. This sequence of the GAA coding region differs from that reported by Hoefsloot et al. (1988) in three areas that change a total of 42 amino acids. Direct determination of the amino acid sequence in one of these areas confirmed the nucleotide sequence reported here but also disagreed with the directly determined amino acid sequence reported by Hoefsloot et al. (1988). At two other areas, changes in base pairs predicted new restriction sites that were identified in cDNAs from several independent libraries. The amino acid changes in all three ares increased the homology to rabbit-human isomaltase. Therefore, we believe that our nucleotide sequence for GAA is more precise. We have also identified single base-pair polymorphisms at 18 sites for human GAA, some of which are not silent.

Amino Acid Sequence↗
PubMed1990

Extensive genetic heterogeneity in patients with acid alpha glucosidase deficiency as detected by abnormalities of DNA and mRNA.

Acid maltase, or acid alpha glucosidase (GAA), is a lysosomal enzyme that hydrolyzes glycogen to glucose and is deficient in glycogen storage disease type II. We have previously isolated a partial cDNA (1.9 kb) for human GAA and detected abnormalities of mRNA in two infantile-onset and one adult-onset patient. We have now extended this study and examined mRNA and DNA from cell lines of eight additional infantile and three adult-onset patients. While five of the 10 infantile-onset patients expressed normal amounts and sizes of mRNA, the remaining five did not express detectable GAA mRNA. Two adult-onset patients had normal amounts and sizes of mRNA, while two adult-onset patients had mRNA of smaller size. Thus, half of the larger series of GAA-deficient patients also exhibited quantitative and/or qualitative abnormalities of mRNA. Of the five infantile-onset patients with normal mRNA, two exhibited an abnormal SacI fragment not found in DNA from 60 normals. To further characterize these patients, we determined GAA activity in several of the cell lines by using either the artificial substrate, 4-methylumbelliferyl-alpha-D-glucoside, or the natural substrate glycogen. Two adult-onset patients who both had normal size mRNA differed as to enzyme activity, with one patient exhibiting enzyme activity similar to that in infantile-onset patients. By combining these data with those for previously reported presence or absence of GAA-mutant protein cross-reacting to antibody, we provide evidence for a minimum of six different mutations in these 14 GAA-deficient cell lines.

Cell Line↗
PubMed1981

Comparison and possible homology of isozymes of adenosine deaminase in Aves and humans.

Two kinetically distinct adenosine deaminase (ADA) isozymes with different molecular weights (35,000 and 100,000 daltons) are found in chicken liver in approximately equal amounts. The 100,000-dalton ADA has a markedly higher Km for adenosine and a markedly lower deaminating activity for deoxyadenosine relative to adenosine than does the 35,000-dalton ADA. A 100,000-dalton ADA isozyme has only recently been detected in mammalian tissues, where, in contrast to the chicken, it is only a trace component of total ADA activity. The human 100,000-dalton ADA isozyme, compared to the human 35,000-dalton ADA isozyme, has been reported to have a higher Km, a lower pH optimum, and a greater resistance to inhibition by erythro-9-(2-hydroxy-2-nonyl) adenine (EHNA). The similarity in KmS of the 100,000-dalton ADA isozyme in man and aves led us to hypothesize that these isozymes might be descended from a common ancestor and therefore also be similar as to other kinetic parameters. We now report that the chicken 100,000-dalton ADA, like the human 100,000-dalton isozyme, has a lower pH optimum and a greater resistance to inhibition by EHNA than does the avian or human 35,000-dalton isozyme. In addition, the avian 100,000-dalton isozyme is relatively resistant to inhibition by deoxycoformycin and has a cathodal rather than an anodal electrophoretic mobility at pH 6.5. Conversely, we report that the human 100,000-dalton ADA isozyme, similar to the avian 100,000-dalton ADA, has markedly lower relative deaminating activity for deoxyadenosine than does the 35,000-dalton ADA human isozyme. Thus, despite the marked difference in the relative amount of the 100,000- and 35,000-dalton ADA isozymes in man as compared to aves, the 100,000-dalton ADA isozymes from both species exhibit several similar kinetic properties, all of which are different from those of the 35,000-dalton ADA isozymes. We also report using a new sensitive assay, relative rates of degradation by the two chicken isozymes of several naturally occurring modified adenine nucleosides which are inhibitory to in vitro human lymphocyte proliferation.

Adenosine Deaminase↗
PubMed1977

RNA and protein components of maize streak and cassava latent viruses.

Polyacrylamide gel electrophoresis indicated that maize streak (MSV) and cassava latent (CLV) viruses each contain one species of protein and two of RNA. The estimated protein mol. wt is 28000 for MSV and 34000 for CLV. The mol. wts obtained for the two RNA species using formamide-containing gels were the same for the two viruses: 1-7 X 10(6) and 1-3 X 10(6). It is suggested that the viruses have a two-part genome and that the tendency of their nucleoprotein particles to form pairs favours the delivery of complete genomes to sites of infection.

Genotype↗
PubMed1977

The health systems agency: a new bureaucracy.

A Federal law signed by President Ford in 1975 (PL 93-641) mandates the establishment of Health Systems Agencies across the country. The major intent of the law is to provide local direction and control of health care planning. Each Agency shall have a professional staff under the aegis of a board of directors composed of a majority of consumers and a minority of providers. Data identifying health care needs shall be translated into a Health Systems Plan, which is a statement of goals for each Agency; an Annual Implementation Plan shall be developed as a statement of objectives, projects, and strategies requisite to achieving the Health Systems Plan. The concept of the Health Systems Agency has correlate state and federal bureaucratic strata to facilitate health care planning coordination.

Community Participation↗