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Biomedical subjects

T G Clark

Publications and source records attributed to T G Clark.

At least 19 recordsLinked to original sources
PubMed2005

Lack of association of the COMT (Val158/108 Met) gene and schizophrenia: a meta-analysis of case-control studies.

There is strong evidence for a genetic contribution to schizophrenia, but the contribution of individual candidate genes remains uncertain. We attempted to replicate a recent meta-analysis that reported an association of the catechol O-methyltransferase (COMT) Val allele with schizophrenia, and suggested that this effect may be moderated by ancestry. We included reports published subsequent to the original meta-analysis, and included a formal test of the moderating effect of ancestry in order to test whether the association operates differently in populations of European ancestry compared to populations of Asian ancestry. A corrected P-value for the 5% significance threshold was employed where appropriate, using Bonferroni's method, and studies that demonstrated departure from Hardy-Weinberg equilibrium among controls were excluded. When all studies were included in a meta-regression, there was evidence for a significant association of COMT Val allele frequency with schizophrenia case status and a significant main effect of ancestry. The interaction of COMT Val allele frequency and ancestry was also significant. However, when only studies that reported allele frequencies that did not depart significantly from Hardy-Weinberg equilibrium among controls were included, these effects were no longer significant. The results of our meta-analysis do not support an association between the COMT Val allele and schizophrenia case status, and do not support recent claims that this association may be moderated by ancestry.

Amino Acid Substitution↗
PubMed2005

Recombinant subunit vaccines: potentials and constraints.

Recombinant DNA techniques have enormous potential for the development of inexpensive, safe and efficacious vaccines for the aquaculture industry. Aside from rationally attenuated pathogens, two broad categories of recombinant vaccines have been described. The first are so-called "vectored" vaccines, which consist of either viral or plasmid expression vectors harbouring genes for protective antigens from a given pathogen. The second are recombinant subunit antigens produced using heterologous protein expression systems. Less onerous from a regulatory standpoint, recombinant subunit vaccines generate strong antibody responses in recipient animals when administered parenterally with adjuvant-containing formulations. This approach is nevertheless constrained by the fact that low-cost systems for protein expression (especially E. coli, but also yeast) often generate misfolded or incorrectly processed membrane antigens that fail to protect, while more complex insect and mammalian tissue culture cells are prohibitively expensive from a production standpoint. Furthermore, subunit antigens generate less than optimal mucosal and cytotoxic T-cell responses, the last two of which are especially important for the clearance of intracellular pathogens. Fortunately, these constraints are now being overcome through the use of new generation adjuvants and delivery systems that enhance immunogenicity, as well as new expression systems for the production of viral and protozoan membrane antigens.

Adjuvants, Immunologic↗
PubMed2003

Creating biological membranes on the micron scale: forming patterned lipid bilayers using a polymer lift-off technique.

We present a new method for creating patches of fluid lipid bilayers with conjugated biotin and other compounds down to 1 microm resolution using a photolithographically patterned polymer lift-off technique. The patterns are realized as the polymer is mechanically peeled away in one contiguous piece in solution. The functionality of these surfaces is verified with binding of antibodies and avidin on these uniform micron-scale platforms. The biomaterial patches, measuring 1 micro m-76 microm on edge, provide a synthetic biological substrate for biochemical analysis that is approximately 100x smaller in width than commercial printing technologies. 100 nm unilamellar lipid vesicles spread to form a supported fluid lipid bilayer on oxidized silicon surface as confirmed by fluorescence photobleaching recovery. Fluorescence photobleaching recovery measurements of DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiIC(18)(3))) stained bilayer patches yielded an average diffusion coefficient of 7.54 +/- 1.25 microm(2) s(-1), equal to or slightly faster than typically found in DiI stained cells. This diffusion rate is approximately 3x faster than previous values for bilayers on glass. This method provides a new means to form functionalized fluid lipid bilayers as micron-scale platforms to immobilize biomaterials, capture antibodies and biotinylated reagents from solution, and form antigenic stimuli for cell stimulation.

Adsorption↗
PubMed2003

Cadmium effects on Ichthyophthirius: evidence for metal-sequestration in fish tissues following administration of recombinant vaccines.

We are developing Tetrahymena thermophila as a delivery system for recombinant vaccines against parasitic protozoa, including the common fish parasite, Ichthyophthirius multifiliis. T. thermophila cell lines expressing I. multifiliis genes under the control of a cadmium-inducible metallothionein gene promoter conferred strong protection against a lethal parasite challenge when administered parenterally to naive fish. Nevertheless, given that heavy metals can be toxic to parasites, a question arose as to whether protection resulted from Cd residues carried over with the vaccine, rather than acquired immunity per se. To address this issue, we examined the sensitivity of I. multifiliis to Cd in vitro and determined Cd concentrations in different host tissues following i.p. injection of juvenile channel catfish with the recombinant vaccine. We found that CdCl2 at concentrations > or = 50 ppb were lethal to I. multifiliis theronts in vitro. Furthermore, Cd concentrations were clearly elevated in fish tissues and reached levels equivalent to 74 ng/g wet weight (74 ppb) in the skin within 14 days of injection with recombinant T. thermophila. Nevertheless, fish injected with non-transformed Tetrahymena grown in the presence or absence of CdCl2 showed no significant difference in either relative survival or parasite load following direct challenge with I. multifiliis.

Animals↗
PubMed2003

Genetic polymorphisms and personality in healthy adults: a systematic review and meta-analysis.

A meta-analysis was conducted on studies reporting data on associations between candidate genes and human personality. Studies reporting data for psychiatric populations (including organic disease and substance abuse) were excluded. A total of 46 studies contributed to the analysis. Pooled data using a fixed-effects model suggested significant associations between the 5HTT LPR, DRD4 c>t, DRD4 length, DRD2 A1/A2, DRD3 A1/A2 polymorphisms and personality traits. A multivariate analysis using a mixed-effects model and including age, sex and predominant ethnicity as covariates was applied to the analyses of 5HTT LPR and DRD4 length polymorphism data. Only the association between the 5HTT LPR polymorphism and avoidance traits remained significant (P=0.038). However, sensitivity analyses excluding data from studies reporting allele frequencies not in Hardy-Weinberg equilibrium and unpublished data resulted in this association no longer being significant. Implications for the design of future association studies of human personality are discussed, including the likely sample sizes that will be required to achieve sufficient power and the potential role of moderating variables such as sex.

Adult↗
PubMed2003

Long term risks of stroke, myocardial infarction, and vascular death in "low risk" patients with a non-recent transient ischaemic attack.

BACKGROUND: Previous studies of prognosis after a transient ischaemic attack (TIA) have recruited patients soon after the event, when the risk of stroke is very high. However, the majority of patients survive for many years after a TIA, and the need for continued preventive treatment to lower vascular risk will need to be reassessed at a later date. OBJECTIVE: To determine the long term risks of stroke and other vascular events in patients with TIA who survive the initial high risk period. METHODS: 290 patients were studied who had initially been followed up after a TIA in the Oxford community stroke project and in a contemporaneous hospital based cohort study, and who were alive and stroke-free at the end of planned follow up in 1988. All patients were followed for a further 10 years, and the risks of major vascular events (stroke, myocardial infarction, vascular death) were determined. Standardised mortality ratios (SMR) were calculated from the observed numbers of fatal events and the number expected on the basis of age and sex in the general population. RESULTS: Median time since last TIA was 3.8 years (interquartile range, 2.2 to 5.8 years). The risk of major vascular events was constant through time. The 10 year risk of first stroke was 18.8% (95% confidence interval (CI), 13.6 to 23.7; 45 events). The 10 year risk of myocardial infarction or death from coronary heart disease was 27.8% (95% CI, 21.8 to 33.3; 67 events) and there was a significant excess of fatal coronary events compared with that expected in the general population (SMR = 1.47; 95% CI, 1.10 to 1.93; p = 0.009). A total of 114 patients had at least one major vascular event, with a 10 year risk of any first stroke, myocardial infarction, or vascular death of 42.8% (95% CI, 36.4 to 48.5). CONCLUSIONS: The overall risk of major vascular events remains high for 10 to 15 years after a TIA. It is important therefore that preventive treatments are continued in the long term, even in apparently "low risk" patients who have already survived free of stroke for several years.

Adult↗
PubMed2001

Gdf5 is expressed in the developing skeleton of median fins of late-stage zebrafish, Danio rerio.

The dynamic expression of Gdf5 is described in the developing skeleton of the median fins of late-stage zebrafish, Danio rerio (6-45 days post-fertilization). In situ hybridization revealed expression in the mesenchyme between cartilage condensations of the endoskeletal supports of the dorsal, anal, and caudal fins. As development proceeds, the expression domains expand distally to surround tips of developing cartilages, consistent with a role in cartilage growth and differentiation. Gdf5 is later expressed in the segmenting regions of the dorsal and anal fin radials, which may indicate a role in segmentation. After growth to 7.5 mm, Gdf5 transcripts can no longer be detected in any of the median fins, nor is Gdf5 expression reinitiated in later development of the median fin skeleton.

Animals↗
PubMed2001

A prognostic model for ovarian cancer.

About 6000 women in the United Kingdom develop ovarian cancer each year and about two-thirds of the women will die from the disease. Establishing the prognosis of a woman with ovarian cancer is an important part of her evaluation and treatment. Prognostic models and indices in ovarian cancer should be developed using large databases and, ideally, with complete information on both prognostic indicators and long-term outcome. We developed a prognostic model using Cox regression and multiple imputation from 1189 primary cases of epithelial ovarian cancer (with median follow-up of 4.6 years). We found that the significant (P< or = 0.05) prognostic factors for overall survival were age at diagnosis, FIGO stage, grade of tumour, histology (mixed mesodermal, clear cell and endometrioid versus serous papillary), the presence or absence of ascites, albumin, alkaline phosphatase, performance status on the ZUBROD-ECOG-WHO scale, and debulking of the tumour. This model is consistent with other models in the ovarian cancer literature; it has better predictive ability and, after simplification and validation, could be used in clinical practice.

Adolescent↗
PubMed2000

Spatiotemporal expression patterns of mammalian chordin during postgastrulation embryogenesis and in postnatal brain.

Chordin is an antagonist of TGFbeta-like bone morphogenetic proteins (BMPs) that plays roles in dorsoventral axis formation and in induction, maintenance and/or differentiation of neural tissue in early vertebrate embryogenesis. In contrast, little is known concerning possible roles for Chordin at later stages of vertebrate development and in the adult. To provide insights into possible postgastrulation roles for Chordin, we report the spatiotemporal expression patterns of Chordin in 8.5- to 15.5-dpc mouse embryos and in the postnatal mouse brain. Expression of Chordin in the primordia of most major organs from 10.5 dpc, including the brain, lung, heart, liver, kidney, thymus, and gut, suggests multiple functions for Chordin in organogenesis, potentially by means of interactions with TGFbeta-like BMPs. The relatively high levels of Chordin expression in condensing and differentiating cartilage elements from 11.5 dpc indicates a generalized role for Chordin throughout embryonic skeletogenesis. In the postnatal mouse brain, we demonstrate that Chordin is coexpressed with other components of the TGFbeta-like BMP signalling pathway in the cerebellum and hippocampus, sites of high synaptic plasticity, suggesting a role for Chordin in this process.

Animals↗
PubMed1999

Mammalian BMP-1/Tolloid-related metalloproteinases, including novel family member mammalian Tolloid-like 2, have differential enzymatic activities and distributions of expression relevant to patterning and skeletogenesis.

Vertebrate bone morphogenetic protein 1 (BMP-1) and Drosophila Tolloid (TLD) are prototypes of a family of metalloproteases with important roles in various developmental events. BMP-1 affects morphogenesis, at least partly, via biosynthetic processing of fibrillar collagens, while TLD affects dorsal-ventral patterning by releasing TGFbeta-like ligands from latent complexes with the secreted protein Short Gastrulation (SOG). Here, in a screen for additional mammalian members of this family of developmental proteases, we identify novel family member mammalian Tolloid-like 2 (mTLL-2) and compare enzymatic activities and expression domains of all four known mammalian BMP-1/TLD-like proteases [BMP-1, mammalian Tolloid (mTLD), mammalian Tolloid-like 1 (mTLL-1), and mTLL-2]. Despite high sequence similarities, distinct differences are shown in ability to process fibrillar collagen precursors and to cleave Chordin, the vertebrate orthologue of SOG. As previously demonstrated for BMP-1 and mTLD, mTLL-1 is shown to specifically process procollagen C-propeptides at the physiologically relevant site, while mTLL-2 is shown to lack this activity. BMP-1 and mTLL-1 are shown to cleave Chordin, at sites similar to procollagen C-propeptide cleavage sites, and to counteract dorsalizing effects of Chordin upon overexpression in Xenopus embryos. Proteases mTLD and mTLL-2 do not cleave Chordin. Differences in enzymatic activities and expression domains of the four proteases suggest BMP-1 as the major Chordin antagonist in early mammalian embryogenesis and in pre- and postnatal skeletogenesis.

Amino Acid Sequence↗
PubMed1999

The gene for an abundant parasite coat protein predicts tandemly repetitive metal binding domains.

Immobilization antigens are highly abundant surface membrane proteins that coat the surface of hymenostomatid ciliates. While their function is unknown, recent studies with the common fish parasite, Ichthyophthirius multifiliis, suggest their involvement in a novel mechanism of humoral immunity involving an effect of antibody on parasite behavior. To gain further insight into the nature of these proteins, we have cloned a gene encoding the 48kDa i-antigen of I. multifiliis. Analysis of the gene (designated IAG48[G1]) reveals a single, uninterrupted reading frame that predicts a protein of 442 amino acids. Based on its deduced amino acid sequence, the protein contains hydrophobic amino acid domains at its N- and C-terminus that are characteristic of signal peptide and GPI-anchor addition sites, respectively. The most striking feature of the predicted protein, however, is a series of tandem repeats that spans most of its length. The repeats themselves are characterized by periodic cysteine residues that fall into register when the homologous segments are aligned. Interestingly, the spacing of cysteines (C-X2,3-C) within a framework of larger (C-X2-C-X20-C-X3-C-X20-C-X2-C) motifs is entirely consistent with the structure of known zinc-binding proteins. Finally, comparison of the coding sequence of the 48kDa i-antigen gene with a partial cDNA previously thought to encode this protein reveals nearly complete identity except at their 3' ends, suggesting that alternative forms of the antigen exist.

Amino Acid Sequence↗
PubMed1999

Structural organization and expression patterns of the human and mouse genes for the type I procollagen COOH-terminal proteinase enhancer protein.

The procollagen C-proteinase enhancer (PCPE) is a glycoprotein that potentiates enzymatic cleavage of the type I procollagen C-propeptide by bone morphogenetic protein-1 (BMP-1). The human PCPE gene (PCOLCE) was previously mapped to 7q22, an area frequently disrupted in uterine leiomyomata, while disruption of the rat PCPE gene leads to anchorage-independent growth and loss of contact inhibition in rat fibroblasts. Here we describe the entire intron/exon organizations of PCOLCE and the mouse PCPE gene (Pcolce) and analyze expression of PCOLCE RNA in various human adult and fetal tissues and of Pcolce RNA at various stages of mouse development. PCOLCE and Pcolce are shown to be small genes 6.0 and 6.5 kb, respectively, with a conserved intron/exon structure comprising 9 exons. A notable difference between the two genes derives from insertion of multiple Alu sequences immediately upstream and downstream and within PCOLCE. Temporal expression of PCPE mRNA is shown to differ from that of BMP-1 and type I procollagen during mouse development, consistent with possible additional functions for PCPE beyond enhancement of C-proteinase activity. Consistent with a possible role in leiomyomata, PCOLCE is shown to be expressed at relatively high levels in uterus.

Adult↗
PubMed1999

Surface display of a parasite antigen in the ciliate Tetrahymena thermophila.

The ciliated protozoan, Tetrahymena thermophila, offers an attractive medium for the expression of heterologous proteins and could prove particularly useful for the display of foreign proteins on the cell surface. Although progress has been made in transformation of Tetrahymena with heterologous DNA, methods that permit reliable expression of foreign genes have been lacking. Using a mutant strain of T. thermophila carrying a negatively selectable allele of a beta-tubulin gene, we have been able to direct foreign genes to this locus by homologous recombination. Transformed cell lines producing foreign proteins were readily identified and, in at least one case, targeting of proteins to the plasma membrane was accomplished.

Animals↗