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W Gibson

Publications and source records attributed to W Gibson.

At least 19 recordsLinked to original sources
PubMed2001

Sex and evolution in trypanosomes.

Trypanosoma brucei is still the only kinetoplastid known to undergo genetic exchange, but it seems unreasonable to suppose that it evolved this process all by itself. The position of T. brucei on a molecular phylogenetic tree constructed from 18S ribosomal RNA gene sequences offers no clues to the likely existence of genetic exchange in trypanosome species other than the Salivaria, because this group of trypanosomes appears to have diverged from the rest a very long time ago. Antigenic variation is one characteristic shared by the Salivaria, which has been particularly well-studied in T. brucei. The large proportion of the genome devoted to variant antigen genes and related sequences in T. brucei, suggests a possible role for genetic exchange in enhancing the diversity of the repertoire. Alternatively, genetic exchange may counter potential excessive double-strand DNA damage brought about by the DNA rearrangements associated with antigenic variation. The remarkable biparental inheritance of organelle DNA (=kinetoplast DNA) in T. brucei is without precedent in other eukaryotes. The result of genetic exchange is to enhance the heterogeneity of the kinetoplast DNA minicircles.

Animals↗
PubMed2001

The molecular evolution of Trypanosomatidae.

In the absence of a fossil record, theories relating to the evolution of protozoa have, for most of the twentieth century, been based on morphological and life cycle data despite their known limitations. However, recent advances in molecular methodology, notably the wide availability of accurate, automated DNA sequencing, have made it possible to deduce the evolutionary relationships of extant species from their genes. This paper focuses on new findings concerning the evolution of the Trypanosomatidae, based on the ever-expanding body of molecular data now available. Classically, the evolution of digenetic parasitism in kinetoplastids has centred around two opposing theories--invertebrate first or vertebrate first--depending on which was the original host of the monogenetic parasite. However, data supporting a close phylogenetic relationship between genera of monogenetic insect parasites and digenetic vertebrate parasites challenge the simplicity of these hypotheses and suggest that the transition may not have been a major evolutionary barrier. The implications of these observations for the evolution of parasitism within the group are discussed. Phylogenetic analysis of a diverse selection of trypanosomatid species suggests that the genus Trypanosoma is monophyletic and that the human parasites, T. brucei, T. cruzi and Leishmania spp., have fundamentally different patterns of evolution. T. brucei clusters with mammalian trypanosomes of African origin, suggesting an evolutionary history confined to Africa. T. cruzi shows association with trypanosomes from bats, T. rangeli, and trypanosomes from a range of South American mammals and an Australian kangaroo. The origins of most parasites within this clade lie in South America and Australia, suggesting an ancient southern super-continent origin for T. cruzi, possibly in marsupials. The divergence between the Leishmania and Trypanosoma lineages is also ancient. The topology of Leishmania phylogenies suggests an independent transition to digenetic parasitism, a neotropical origin and an early tertiary radiation of the parasite.

Animals↗
PubMed2001

Molecular characterization of field isolates of human pathogenic trypanosomes.

The accurate identification of each of the three subspecies of Trypanosoma brucei remains a challenging problem in the epidemiology of sleeping sickness. Advances in molecular characterization have revealed a much greater degree of heterogeneity within the species than previously supposed. Only group 1 T. b. gambiense stands out as a separate entity, defined by several molecular markers. T. b. rhodesiense is generally too similar to sympatric T. b. brucei strains to be distinguished from them by any particular molecular markers. Nevertheless, characterization of trypanosome isolates from humans and other animals has allowed the identification of potential reservoir hosts of T. b. rhodesiense. The recent discovery of a gene for human serum resistance may provide a useful marker for T. b. rhodesiense in the future. There have been few attempts to find associations between genetic markers and other biological characters, except human infectivity. However, virulence or fly transmissibility have been correlated with molecular markers in some instances.

Africa↗
PubMed2001

Cytomegalovirus basic phosphoprotein (pUL32) binds to capsids in vitro through its amino one-third.

The cytomegalovirus (CMV) basic phosphoprotein (BPP) is a component of the tegument. It remains with the nucleocapsid fraction under conditions that remove most other tegument proteins from the virion, suggesting a direct and perhaps tight interaction with the capsid. As a step toward localizing this protein within the molecular structure of the virion and understanding its function during infection, we have investigated the BPP-capsid interaction. In this report we present evidence that the BPP interacts selectively, through its amino one-third, with CMV capsids. Radiolabeled simian CMV (SCMV) BPP, synthesized in vitro, bound to SCMV B-capsids, and C-capsids to a lesser extent, following incubation with either isolated capsids or lysates of infected cells. Human CMV (HCMV) BPP (pUL32) also bound to SCMV capsids, and SCMV BPP likewise bound to HCMV capsids, indicating that the sequence(s) involved is conserved between the two proteins. Analysis of SCMV BPP truncation mutants localized the capsid-binding region to the amino one-third of the molecule--the portion of BPP showing the greatest sequence conservation between the SCMV and HCMV homologs. This general approach may have utility in studying the interactions of other proteins with conformation-dependent binding sites.

Amino Acid Sequence↗
PubMed2000

Structure and sequence variation of the trypanosome spliced leader transcript.

We have assessed the potential of using the spliced leader (SL) or mini-exon gene as a marker for molecular phylogenetic analysis of genus Trypanosoma. A total of 27 trypanosome sequences were compared, 18 of these being newly reported. In contrast to genus Leishmania, we found the non-transcribed spacer region of the SL locus in trypanosomes to be far too variable for informative comparison of all but the most closely related species. At the other extreme, the short (39 nt) SL exon was usually completely conserved and hence uninformative. The SL RNA showed variation in both length (97-152 nt) and sequence among different trypanosome species, with most variation occurring in stem-loop II. Consequently, this region could not be aligned with confidence in multiple sequence alignment, severely reducing the number of phylogenetically informative nucleotide positions. In computer simulation, most of the SL RNAs readily folded into the 3 stem-loop secondary structure predicted previously, but again stem-loop II was highly variable. No obvious correlation could be seen between the length of this stem-loop and trypanosome biology. We conclude that the SL repeat is not an informative phylogenetic marker for long range evolutionary studies of genus Trypanosoma.

Animals↗
PubMed2000

Characterization of Trypanozoon isolates using a repeated coding sequence and microsatellite markers.

Genetic variation of microsatellite loci is a widely used method for linkage analysis, individual identification or inter-population studies. Here we analyse a repeated DNA coding sequence and eleven new microsatellites identified within the Trypanosoma (Trypanozoon) brucei genome. Ninety-seven isolates belonging to the five species and subspecies Trypanosoma evansi, T. equiperdum, T. brucei brucei, T. b. rhodesiense and T. b. gambiense were compared regarding the genetic patterns of these markers. The results reveal a great heterogeneity of the genotypes related to the repeated coding sequence and five microsatellites, some of which show a high degree of polymorphism. This allows us to define group-specific genotypes or alleles; in particular, we show that one specific pattern clearly segregates the human pathogen T. b. gambiense group I.

Amino Acid Sequence↗
PubMed2000

Characterization of Trypanozoon isolates using a repeated coding sequence and microsatellite markers.

Genetic variation of microsatellite loci is a widely used method for linkage analysis, individual identification or inter-population studies. Here we analyse a repeated DNA coding sequence and eleven new microsatellites identified within the Trypanosoma (Trypanozoon) brucei genome. Ninety-seven isolates belonging to the five species and subspecies Trypanosoma evansi, T. equiperdum, T. brucei brucei, T. b. rhodesiense and T. b. gambiense were compared regarding the genetic patterns of these markers. The results reveal a great heterogeneity of the genotypes related to the repeated coding sequence and five microsatellites, some of which show a high degree of polymorphism. This allows us to define group-specific genotypes or alleles; in particular, we show that one specific pattern clearly segregates the human pathogen T. b. gambiense group 1.

Journal Article↗
PubMed2000

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Journal Article↗
PubMed2000

Comparison between African-American and white women in their beliefs about breast cancer and their health locus of control.

The purpose of this study was to examine the health beliefs of African-American and white women about breast cancer and locus of control, using the health belief model and the health locus of control construct. The Health Screening Questionnaire, developed by Sugarek, Deyo, and Holmes, was used to collect self-report data about health beliefs related to breast cancer and health locus of control. Participants included 197 white and 152 African-American women, between the ages of 19 and 93, recruited from various settings in central Florida. Significant differences were found between the two groups on all of the health beliefs about cancer items. The African-American women were significantly more likely to believe in chance, or to depend on powerful others for their health. Perceived susceptibility to cancer, doubts about the value of early diagnosis, and beliefs about the seriousness of breast cancer all were significantly associated with powerful other scores among African-American women. There was no relation between health beliefs and years of education for African-American women, but for white women, those with the least education were more likely to believe that death was inevitable with a cancer diagnosis. These results add to the information needed for the development of effective programs aimed at increasing breast cancer screening among African-American women.

Adult↗
PubMed1999

Genetic exchange in the trypanosomatidae.

The only trypanosomatid so far proved to undergo genetic exchange is Trypanosoma brucei, for which hybrid production after co-transmission of different parental strains through the tsetse fly vector has been demonstrated experimentally. Analogous mating experiments have been attempted with other Trypanosoma and Leishmania species, so far without success. However, natural Leishmania hybrids, with a combination of the molecular characters of two sympatric species, have been described amongst both New and Old World isolates. Typical homozygotic and heterozygotic banding patterns for isoenzyme and deoxyribonucleic acid markers have also been demonstrated amongst naturally-occurring T. cruzi isolates. The mechanism of genetic exchange in T. brucei remains unclear, although it appears to be a true sexual process involving meiosis. However, no haploid stage has been observed, and intermediates in the process are still a matter for conjecture. The frequency of sex in trypanosomes in nature is also a matter for speculation and controversy, with conflicting results arising from population genetics analysis. Experimental findings for T. brucei are discussed in the first section of this review, together with laboratory evidence of genetic exchange in other species. The second section covers population genetics analysis of the large body of data from field isolates of Leishmania and Trypanosoma species. The final discussion attempts to put the evidence from experimental and population genetics into its biological context.

Animals↗
PubMed1999

The molecular evolution of trypanosomes.

The absence of a fossil record has meant that the evolution of protozoa has remained largely a matter for speculation. Recent advances in molecular biology and phylogenetic analysis, however, are allowing the 'history written in the genes' to be interpreted. Here, Jamie Stevens and Wendy Gibson review progress in reconstruction of trypanosome phylogeny based on molecular data from rRNA and protein-coding genes.

Africa↗
PubMed1999

Congenital insensitivity to pain with anhidrosis: novel mutations in the TRKA (NTRK1) gene encoding a high-affinity receptor for nerve growth factor.

Congenital insensitivity to pain with anhidrosis (CIPA) is characterized by recurrent episodes of unexplained fever, anhidrosis (inability to sweat), absence of reaction to noxious stimuli, self-mutilating behavior, and mental retardation. Human TRKA encodes a high-affinity tyrosine kinase receptor for nerve growth factor (NGF), a member of the neurotrophin family that induces neurite outgrowth and promotes survival of embryonic sensory and sympathetic neurons. We have recently demonstrated that TRKA is responsible for CIPA by identifying three mutations in a region encoding the intracellular tyrosine kinase domain of TRKA in one Ecuadorian and three Japanese families. We have developed a comprehensive strategy to screen for TRKA mutations, on the basis of the gene's structure and organization. Here we report 11 novel mutations, in seven affected families. These are six missense mutations, two frameshift mutations, one nonsense mutation, and two splice-site mutations. Mendelian inheritance of the mutations is confirmed in six families for which parent samples are available. Two mutations are linked, on the same chromosome, to Arg85Ser and to His598Tyr;Gly607Val, hence, they probably represent double and triple mutations. The mutations are distributed in an extracellular domain, involved in NGF binding, as well as the intracellular signal-transduction domain. These data suggest that TRKA defects cause CIPA in various ethnic groups.

Base Sequence↗
PubMed1999

Phosphorylation of simian cytomegalovirus assembly protein precursor (pAPNG.5) and proteinase precursor (pAPNG1): multiple attachment sites identified, including two adjacent serines in a casein kinase II consensus sequence.

The assembly protein precursor (pAP) of cytomegalovirus (CMV), and its homologs in other herpesviruses, functions at several key steps during the process of capsid formation. This protein, and the genetically related maturational proteinase, is distinguished from the other capsid proteins by posttranslational modifications, including phosphorylation. The objective of this study was to identify sites at which pAP is phosphorylated so that the functional significance of this modification and the enzyme(s) responsible for it can be determined. In the work reported here, we used peptide mapping, mass spectrometry, and site-directed mutagenesis to identify two sets of pAP phosphorylation sites. One is a casein kinase II (CKII) consensus sequence that contains two adjacent serines, both of which are phosphorylated. The other site(s) is in a different domain of the protein, is phosphorylated less frequently than the CKII site, does not require preceding CKII-site phosphorylation, and causes an electrophoretic mobility shift when phosphorylated. Transfection/expression assays for proteolytic activity showed no gross effect of CKII-site phosphorylation on the enzymatic activity of the proteinase or on the substrate behavior of pAP. Evidence is presented that both the CKII sites and the secondary sites are phosphorylated in virus-infected cells and plasmid-transfected cells, indicating that these modifications can be made by a cellular enzyme(s). Apparent compartmental differences in phosphorylation of the CKII-site (cytoplasmic) and secondary-site (nuclear) serines suggest the involvement of more that one enzyme in these modifications.

Amino Acid Sequence↗
PubMed1999

Capsid structure of simian cytomegalovirus from cryoelectron microscopy: evidence for tegument attachment sites.

We have used cryoelectron microscopy and image reconstruction to study B-capsids recovered from both the nuclear and the cytoplasmic fractions of cells infected with simian cytomegalovirus (SCMV). SCMV, a representative betaherpesvirus, could thus be compared with the previously described B-capsids of the alphaherpesviruses, herpes simplex virus type 1 (HSV-1) and equine herpesvirus 1 (EHV-1), and of channel catfish virus, an evolutionarily remote herpesvirus. Nuclear B-capsid architecture is generally conserved with SCMV, but it is 4% larger in inner radius than HSV-1, implying that its approximately 30% larger genome should be packed more tightly. Isolated SCMV B-capsids retain a relatively well preserved inner shell (or "small core") of scaffolding-assembly protein, whose radial-density profile indicates that this protein is approximately 16-nm long and consists of two domains connected by a low-density linker. As with HSV-1, the hexons but not the pentons of the major capsid protein (151 kDa) bind the smallest capsid protein (approximately 8 kDa). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed cytoplasmic B-capsid preparations to contain proteins similar in molecular weight to the basic phosphoprotein (approximately 119 kDa) and the matrix proteins (65 to 70 kDa). Micrographs revealed that these particles had variable amounts of surface-adherent material not present on nuclear B-capsids that we take to be tegument proteins. Cytoplasmic B-capsids were classified accordingly as lightly, moderately, or heavily tegumented. By comparing the three corresponding density maps with each other and with the nuclear B-capsid, two interactions were identified between putative tegument proteins and the capsid surface. One is between the major capsid protein and a protein estimated by electron microscopy to be 50 to 60 kDa; the other involves an elongated molecule estimated to be 100 to 120 kDa that is anchored on the triplexes, most likely on its dimer subunits. Candidates for the proteins bound at these sites are discussed. This first visualization of such linkages makes a step towards understanding the organization and functional rationale of the herpesvirus tegument.

Capsid↗