Browsing by Autor "Tibayrenc, M"

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A genetic comparison between Brazilian and Bolivian zymodemes of Trypanosoma cruzi
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1983) Tibayrenc, M
Abstract. The enzyme profiles of three major Brazilian Trypanosoma cruzi zymodemes (Brazilian Z1, Brazilian Z2, Brazilian Z3) and of two principal Bolivian zymodemes were compared. Relationships were assessed both intuitively and by calculating genetic distances. One of the Bolivian zymodemes, Bolivian Z1, was closely related to the Brazilian Z1. The second Bolivian zymodeme, Bolivian Z2, was related to brazilian Z2 but differed from all the Brazilian zymodemes in the occurrence of typical heterozygous isozyme patterns in five out of 12 enzyme loci. Parental stocks and clones of Bolivian Z2 had the same putative heterozygous patterns. The evidence from enzyme profiles on the ploidy of T. cruzi and the possibility of recombination was considered. The presence of putative heterozygous patterns in Bolivian Z2 supported the hypothesis that T. cruzi is diploid. The definition of T. cruzi as a single polytypic species or as a species complex was considered to be dependent on the presence or absence of genetic recombination between or within the zymodemes, which has not been demonstrated in the ecotopes so far examined.
Addional data on Trypanosoma cruzi isozymic strains encountered in Bolivian domestic transmission cycles
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1986) Tibayrenc, M
Abstract. We have collected in Bolivia 212 stocks of Trypanosoma cruzi from domestic transmission cycles and have assayed for nine enzyme systems (11 gene loci). Only a few different isozyme profiles exist, without recombination between them, a situation also encountered in previous Bolivian samples. The 212 stocks, combined with 207 stocks previously studied, have been analysed to uncover any spatial patterns. The frequency of heterozygous strains (2 and 2a) decreases westwards and with increasing altitude. Given that longitude and altitude are correlated with each other, it is not possible to decide which of these two geographic variables is the relevant one, or if both are. These associations might be due to climatic factors. Studies by other authors have shown, however, that heterozygous strains are rare or absent in the Amazon Basin, which is at low altitude.
General classification of the isoenzymic strains of Trypanosoma (Schizotrypanum) cruzi and comparison with T. (S.) C. Marinkellei and T. (Herpetosoma) rangeli
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1984) Tibayrenc, M
Summary. Thirteen laboratory reference stocks of Trypanosoma (Schizottypanum) cruzi were classified according to genetic distance by enzyme analysis of 14 loci. Three principal isoenzymic strains were recognized together with 6 lesser ones. These patterns fall within our previous classification, suggesting that by now the main bulk of T. cruzi enzymic variability has been recognized. Consequently it should be possible to identify any T. cruzi stock with certainty and to assess whether cruzi-like organisms belong to the cruzi complex. T. (S) cruzi marinkellei and T. (H.) rangeli reference stocks were also compared. These two taxa showed to be different from the T. cruzi strains, but it was necessary to use a large set of enzymes before gaining evidence for this.
Isozymic variability of Trypanosoma cruzi : biological and epidemiological significance
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1985) Tibayrenc, M
Summary. Genetic interpretation of. T. cruzi zymograms has led to various hypotheses which are reviewed.
New electrophoretic evidence of genetic variation and diploidy in Trypanosoma cruzi, the causative agent of Chagas' disease
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1985) Tibayrenc, M
Abstract. By changing clcctrophoretic conditions additional genetic variability was observed in both previously and newly analysed enzymatic systemes in Trypanosoma cruzi . Inferences the quaternary structure of enzymes emerge from the electrophoretic patterns. The results of the present work are consistent with those obtained formerly in supporting both diploidy and lack of mating. These observations are relevant to the main question of the evolutionary origin of T. cruzi isozymic strains.
The microdistribution of isoenzymic strains of Trypanosoma cruzi in southern Bolivia; new isoenzyme profiles and further arguments against Mendelian sexuality
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1984) Tibayrenc, M
Abstract. 132 Trypanosoma cruzi stocks were collected in southern Bolivia (99 stocks in Tupiza, 33 in Tarija), and were characterized using five enzymes (six loci). From these 132 stocks, a sample of 21 was studied using 10 enzymes (12 loci) to establish the genetic distances between them. Only five different isoenzymic strains were registered among the 132 stocks: the taxonomic status of these strains is discussed. The distribution of the strains indicated that a Founder effect was not a constant fact at the level of the house and of the suburb, but that a Founder effect was more apparent for greater geographical distances. All strains were transmitted sympatrically by the same vector Triatoma infestans. Genotype frequencies demonstrated the lack of Mendelian sexuality among stocks of T. cruzi from southern Bolivia, confirming our previous results.
Trypanosoma cruzi populations : more clonal than sexual
(Facultad de Medicina, Enfermería, Nutrición y Tecnología Médica, 1987) Tibayrenc, M
The ancient guestion of trypanosome sexuality has recently been reactivated in view of important observations in the African species Trypanosoma brucie, in which Mendelian sexuality has been proposed as o working hypothesis on the basis of indirect isozyme evidencer. Subsequent experiments have confirmed that recombination can occur in T. brucei under defined experimental conditions and suggest that this parasite undergoes meiosis2-4. ln this article, Michel Tbayrenc and Francisco Ayalo discuss the intraspecific variability of another species, Trypanosoma cruzi - causative agent of american trypanosomiasis or Chagas disease. They interpret the variation revealed by extensive isozyme analysis and restriction endonuclease analysis of kinetoplast DNA, to suggest that T. cruzi is diploid, genetically very polymorphic, and has a clonal structure that manifest a lack of (or very restricted) sexuality.