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D Le Ray

Publications and source records attributed to D Le Ray.

At least 55 records · Page 3Linked to original sources
PubMed1995

Plasticity of gp63 gene organization in Leishmania (Viannia) braziliensis and Leishmania (Viannia) peruviana.

The genomic organization of gp63 genes in 4 and 7 isolates of Leishmania braziliensis and L. peruviana, respectively was studied by RFLP analysis with 3 restriction enzymes (Bgl I, Sal I and Apa I). Our results showed a marked polymorphism among isolates. Some characters were specific to L. braziliensis or to L. peruviana, and others specific to the respective biogeographical populations of L. peruviana. The average minimum copy number of gp63 genes was found to be higher in L. braziliensis (71) than in L. peruviana (46), suggesting that deletion of gp63 genes might be partially involved in the size decrease of the chromosome bearing gp63 genes, observed between those 2 species (from 700 to 610 kb). Our results may suggest the existence of at least 2 arrays of heterologous gp63 repeats, varying in relative copy number between L. braziliensis and L. peruviana, and among isolates of the latter species. Rearrangement of the gp63 genes was observed during long-term in vitro maintenance of a reference strain of L. braziliensis. These observations document the existence of a dynamic gp63 gene organization in Leishmania of the braziliensis complex.

Animals↗
PubMed1995

The EUROLEISH network: an exercise in partnership.

The EUROLEISH network arose in 1989 as a spontaneous initiative from contract holders funded by the health component of the Science and Technology for Development programme of the European Commission (EC). Leishmaniasis projects from other programmes (International Scientific Co-operation and Avicenna) joined the network later on. The network has three central objectives: to improve interactions between laboratory and field scientists; to rank the queries raised by health services in order of importance for research; and to develop partnerships between European countries and between these and developing countries. The EUROLEISH network is run consensually by the contract-holders and meets yearly, the subject of each meeting alternating between biology (in Europe) and epidemiology (in an endemic country). Presently, the network comprises 66 contract-holders from 18 projects in 28 countries, with a research budget of 4.6 million ecus during the Third EC Framework Programme (1990-1994). The next main issue to be addressed by the network will probably be the strengthening of thematic research, by promoting 'bridge building' between projects at regional level.

Forecasting↗
PubMed1995

From population to genome: ecogenetics of Leishmania (Viannia) braziliensis and L. (V.) peruviana.

The size polymorphism of nine chromosomes, recognized by specific probes, was analysed in populations of Leishmania (Viannia) braziliensis and L. (V.) peruviana from various Peruvian biogeographical units. Interpretation of the polymorphism, by statistical and phenetic methods, led to the identification of five consensus (alpha- and beta-tubulin) and four variable chromosomes. The dynamics of the variable chromosomes were studied. The promoter role of the environment on their polymorphism was indicated by: (1) the discrimination of L. braziliensis (forest) and L. peruviana (Andes) by the size of the chromosome containing the gp63 genes; and (2) the fact that, within L. peruviana, the polymorphism of the variable chromosomes revealed a strong eco-geographical structuring of parasite populations, accompanied by increasing chromosomal dissimilarity along a cline from north to south. The adaptative significance of the polymorphism of the variable chromosomes was suggested by: (1) a correlation between chromosomal polymorphism and phenotype variability (lesion type in patients and virulence in vitro); and (2) the association between the decrease in size of the gp63-containing chromosome from L. braziliensis to L. peruviana, and a rearrangement of the gp63 genes, probably accompanied by a decrease in their copy number. As chromosomal variation was shown to be more dependant on eco-geographical differences than isoenzymatic variation, chromosome variation and enzyme variation probably differ in adaptative significance.

Adaptation, Biological↗
PubMed1994

Cytogenetic and isozymic comparisons of two laboratory lines of Glossina palpalis gambiensis.

The genetics of two laboratory colonies of Glossina palpalis gambiensis were characterized by C-banding and isoenzyme studies. The colonies, derived from flies collected in the same locality, had different histories in the laboratory and different susceptibilities to trypanosome infection. Although the two lines were also found to differ in the frequencies of chromosome and isozyme variants, the variation was not enough to put their specific status in doubt; it was probably the result of genetic drift since the foundation of the colonies.

Animals↗
PubMed1993

The ble resistance gene as a new selectable marker for Trypanosoma brucei: fly transmission of stable procyclic transformants to produce antibiotic resistant bloodstream forms.

We describe here the stable transformation of Trypanosoma brucei using a new selectable marker for kinetoplastid protozoa, the Sh ble, or phleomycin, resistance gene. A plasmid containing this gene targeted to the tubulin gene locus by homologous sequences was introduced into procyclic trypanosomes by electroporation and cells selected for antibiotic resistance. Southern analysis of stable transformants showed that the plasmid had been integrated into the tubulin locus by homologous recombination. Analysis of bloodstream stage transformants, produced by transmission through the vector Glossina, showed that the resistance gene was conserved and expressed in these forms in the absence of selective drug pressure. In both procyclic and bloodstream forms, transcription of the ble gene appears to originate from the upstream tubulin promoter, despite the presence of a VSG promoter in the integrated construct. The generation of stable bloodstream transformants for the first time will facilitate the study of gene function and expression during the trypanosome life cycle, and aid in the investigation of genetic exchange in these organisms.

Animals↗
PubMed1993

Transient adenylate cyclase activation accompanies differentiation of Trypanosoma brucei from bloodstream to procyclic forms.

Pleomorphic bloodstream forms of Trypanosoma brucei differentiate synchronously into procyclic forms when cultivated at 27 degrees C in the presence of citrate/cis-aconitate. The activity of adenylate cyclase was monitored during this process. Two phases of transient stimulation were observed. The first phase occurred 6-10 h after the triggering of differentiation, a period which immediately follows the release of the bulk of the VSG and immediately precedes both the first cell division and the loss of the bloodstream-specific ESAG 4 transmembrane adenylate cyclase. The second phase occurred between 20 and 40 h, when the cells that emerged from the first division began to proliferate. These observations suggest that cAMP may be involved in differentiation/proliferation of the parasite.

Adenylyl Cyclases↗
PubMed1991

Chromosome rearrangement in Leishmania mexicana M379.

Circular extrachromosomal elements were observed in a variety of Leishmania species. We show here that two lines originating from the same isolate have been found to contain a circular DNA molecule of 26.6 kb and a linear chromosome of about 250 kb, respectively, which share a homology of more than 20 kb. The circular DNA molecule and its related region on the linear chromosome were cloned and their restriction maps compared. This investigation reveals information about chromosome rearrangement in L. mexicana M379. Further examination will enable us to understand the nature of chromosome rearrangement such as circularization or linearization.

Animals↗
PubMed1991

[SDS-PAGE analysis of surface proteins and antigens evidences high heterogenity in natural clones of Trypanosoma cruzi, correlated with isoenzyme variability].

Surface protein and surface antigen patterns of 19 Trypanosoma cruzi laboratory clones, representing 17 different isozymic profiles (zymodemes), were compared by SDS-PAGE analysis. Surface protein patterns were found to be complex and heterogeneous. According to the number of common bands, we calculated similarity coefficients of surface protein patterns on the one hand, and of surface antigen patterns on the other hand, for 33 stock pairwise comparisons. In both cases, these coefficients were statistically correlated to the isozyme index of genetic identity. Such a correlation between independent genetic markers favours the clonal structure of T. cruzi natural populations previously evidenced. Moreover, we did not observe any notable differences in the surface antigen pattern among 4 T. cruzi cloned stocks precipitated by homologous as well as heterologous hyperimmune sera. The immunological significance of the molecular weight variability in surface antigen patterns among different zymodemes is discussed.

Animals↗
PubMed1989

Vector susceptibility to African trypanosomes.

Susceptibility of tsetse fly to trypanosome depends on two distinct barriers controlling respectively colonization of midgut and, migration to salivary glands. Those barriers are modulated by barely known factors, pertaining to the physiological status of the fly as well as to cytoplasmic and nuclear inheritance. Quantification of colonization (p) and migration (m) rates provides a way to calculate intrinsic vectorial capacity (IVC) as a product IVC = p x m, and to undergo comparative analysis of underlying factors.

Animals↗
PubMed1987

Characterization of genes coding for two major metacyclic surface antigens in Trypanosoma brucei.

In African trypanosomes, only a very small fraction of the total repertoire of variable antigen types (VATs) is expressed by the metacyclic form. In Trypanosoma brucei stock EATRO 1125, the VATs AnTat 1.30 and 1.45 are reproducibly present in about 15% and 4% of the metacyclic population, respectively. The genes encoding the corresponding antigens or variant surface glycoproteins (VSGs) are in telomeres of large chromosomes, as are some non-metacyclic VSG genes from the same stock. Their activation mechanism has been studied in seven independent clones, 3 of which, referred to as 'first wave' metacyclic VATs (M-VATs), have been cloned from the first wave of parasitemia after cyclic transmission. In all these clones, activation of the antigen gene was linked to the transposition of an expression linked copy (ELC) of the gene to a telomeric expression site. For first wave M-VATs, this site seems variable, although restricted to large chromosomes, and it can be re-used for VSG gene expression in the bloodstream form. In 'late bloodstream' M-VATs, isolated from established chronic infections, the active expression site, at the end of a 200 kb chromosome, is the one preferred for the expression of late antigen types. It can be concluded that no characteristic feature in the genomic location and expression mechanism can distinguish metacyclic antigen genes from those expressed in the bloodstream forms, although the control of their expression must clearly be different.

Animals↗
PubMed1986

The use of DNA hybridization and numerical taxonomy in determining relationships between Trypanosoma brucei stocks and subspecies.

The nuclear DNAs of 71 trypanosome stocks from different African countries, representative of the three Trypanosoma brucei subspecies, and one T. evansi stock, have been analysed by the combined use of restriction endonuclease digestion, gel electrophoresis and molecular hybridization with both trypanosome surface-antigen-specific and undefined genomic DNA probes. In contrast with T. brucei brucei and T. brucei rhodesiense stocks, all the T. b. gambiense stocks are characterized by a conserved, specific DNA band pattern, regardless of the probe. This allows T. b. gambiense to be non-ambiguously identified. On the contrary, T.b. brucei and T. b. rhodesiense, which could not be discriminated by the same criteria, both yield highly variable DNA band patterns. Our data confirm that domestic animals like pig, dog and sheep constitute a potential reservoir for T.b. gambiense. Using a numerical analysis of the DNA hybridization patterns we have measured the degree of similarity between the 72 trypanosome stocks. This investigation shows that all T.b. gambiense stocks are included in the same homogeneous population, while the stocks from the two other subspecies seem to be distributed in several heterogeneous groups, some of these showing correlation with the geographical origin of the trypanosomes. It is concluded that (i) T.b. gambiense stands out as a real subspecies that has undergone a distinct evolution relative to the 'non-gambiense' group, (ii) the alleged T.b. rhodesiense subspecies does not fit with any of the groups evidenced by our cladistic analysis and hence does not appear as a distinct subspecies and (iii) 'non-gambiense' trypanosomes are probably evolving much more rapidly than T.b. gambiense. Different aspects of trypanosome relationships and evolution are discussed.

Africa↗
PubMed1986

Specific and sensitive immunological diagnosis of Chagas' disease by competitive antibody enzyme immunoassay using a Trypanosoma cruzi-specific monoclonal antibody.

Coexistence of Chagas' disease with leishmaniasis and T. rangeli infection in endemic areas and cross-reactivity between corresponding etiological agents can confuse the immunodiagnosis of Chagas' disease. A discriminative serological test could therefore represent a major advance in specific immunodiagnosis. A competitive antibody enzyme immunoassay against a component 5-enriched preparation, using a T. cruzi species-specific monoclonal antibody has allowed development of a specific serodiagnosis of Chagas' disease with high sensitivity (96.6% in undetermined and chronic phases of infection). This test can differentiate Chagas' disease from other cross-reacting parasitic diseases in areas where concomitant infections are unknown or suspected.

Animals↗
PubMed1985

Inactivation and reactivation of a variant-specific antigen gene in cyclically transmitted Trypanosoma brucei.

In Trypanosoma brucei, the activation of the variant-specific antigen gene AnTat 1.1 proceeds by the synthesis of an additional gene copy, the AnTat 1.1 ELC, which is transposed to a new location, the expression site, where it is transcribed. Using the AnTat 1.1 variant to infect flies, we investigated the fate of the AnTat 1.1 ELC during cyclic transmission of T. brucei. We show here that the AnTat 1.1 ELC is conserved in procyclic trypanosomes, obtained either from the midgut of infected Glossina or from cultures, and in metacyclic trypanosomes, although the AnTat 1.1 serotype is not detected among metacyclic antigen types. This same AnTat 1.1 ELC, which is thus silent as the parasite develops in the insect vector, can be reactivated without duplication during the first parasitemia wave following cyclical transmission. This re-expression of the conserved ELC accounts for the early appearance of the 'ingested' antigenic type after passage through the fly.

Animals↗