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PubMed1998

[The biological characterization of HIV-1 isolated in patients with a rapid clinical evolution].

The biological characteristics of 11 HIV-1 strains isolated from patients with a fast clinical evolution to AIDS were studied. The viral isolates were classified according to their replication kinetics and cell tropism. Taking into account these criteria, it was observed that 8 of the isolated strains (72.7%) were of rapid high growth (RH) or slow low 3 (SL3) with preferential tropism to the lymphocytic stock, as it corresponds to AIDS patients. 3 (27.3%) had characteristics of slow low 1 (SL1). The cytopathogenicity of the strains was studied in the MT4 cellular line, and it was observed that most of them (72.7%) were syncytium-inducing strains (SI), which allowed to prove the in vivo and in vitro relation of the biological properties. It was not so in 3 of the cultures (27.3%) that behaved as non-syncytium inducers.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Trypanosoma cruzi: impact of clonal evolution of the parasite on its biological and medical properties.

Trypanosoma cruzi populations are subdivided into natural clones that can exhibit considerable genetic differences. It has been proposed that T. cruzi clonal structure has a major impact on this parasite's biological properties. The present work aims at testing this hypothesis. Twenty-one stocks isolated from various ecological cycles, places, and hosts were characterized by multilocus enzyme electrophoresis (MLEE) with 22 genetic loci and random amplification of polymorphic DNA (RAPD) with 10 primers on the one hand and by 14 different biological parameters on the other hand. These parameters were related to: (i) growth kinetics of epimastigotes and amastigotes; (ii) infection of culture cells by amastigotes; (iii) viability of extracellular trypomastigotes; or (iv) sensitivity of epimastigotes, trypomastigotes, and amastigotes to Benznidazole and Nifurtimox. MLEE and RAPD results exhibited parity to each other, as previously noted (M. Tibayrenc, K. Neubauer, C. Barnabé, F. Guerrini, D. Skarecky, and F. J. Ayala, 1993, Proceedings of the National Academy of Sciences of the USA 90, 1335-1339), and showed that the 21 stocks were distributed into three main genetic groups, 19/20, 32, and 39, corresponding to the major clones 19, 20, 32, and 39 previously described on the basis of 15 isozyme loci. Most biological parameters showed a strong correlation to the genetic distances evaluated from either MLEE or RAPD, which favors the working hypothesis. The only exception came from drug sensitivity estimated on trypomastigote forms. The overall results made it possible to firmly reject the null hypothesis that there is no relationships between evolutionary distances and biological differences in T. cruzi natural clones.

Animals↗
PubMed2002

Comparative methods and evolution.

Comparative biology provides a framework for the study of evolution, by seeking answers to the question of why traits evolved. However, the difficulties of making inferences about the biological causes of trait variation and covariation resulted in the development of very different approaches to comparative analyses, which are outlined and contrasted here. The Homology approach differs from all other approaches as it attempts to explain historical uniques, whereas the various homoplasy approaches draw inferences from repeated origination of correlated traits. A distinction is made between those approaches deriving information from correlated transitions of characters on a cladogram (Homoplasy I) and those that simply extract correlated differences between pairs of phylogenetically independent taxa (Homoplasy II). The latter approach has been implemented in well-developed analytical procedures ("comparative methods") which, however, are principally non-historical and thus their inferences about evolution are indirect. In contrast, the study of correlation of character transitions seeks to explain trait variation as the outcome of evolution, but is hampered by the difficulty of reconstructing ancestral character states, a prerequisite for the analysis of correlated transitions. Model-based techniques for ancestral state reconstruction are being developed, but the lack of data contained in single characters limits the biological reality of parameter-intensive models.

Animals↗