Extensive microsatellite diversity in the human malaria parasite Plasmodium vivax

The population structure of Plasmodium vivax remains elusive. The markers of choice for large-scale population genetic studies of eukaryotes, short tandem repeats known as microsatellites, have been recently reported to be less polymorphic in R vivax. Here we investigate the microsatellite diversity and geographic structure in P vivax, at both local and global levels, using 14 new markers consisting of tri- or tetranucleotide repeats. The local-level analysis, which involved 50 field isolates from Sri Lanka, revealed unexpectedly high diversity (average virtual heterozygosity [H-E], 0.807) and significant multilocus linkage disequilibrium in this region of low malaria endemicity. Multiple-clone infections occurred in 60% of isolates sampled in 2005. The global-level analysis of field isolates or monkey-adapted strains identified 150 unique haplotypes among 164 parasites from four continents. Individual P. vivax isolates could not be unambiguously assigned to geographic populations. For example, we found relatively low divergence among parasites from Central America, Africa, Southeast Asia and Oceania, but substantial differentiation between parasites from the same continent (South Asia and Southeast Asia) or even from the same country (Brazil). Parasite relapses, which may extend the duration of P. vivax carriage in humans, are suggested to facilitate the spread of strains across continents, breaking down any pre-existing geographic structure. (C) 2008 Elsevier B.V. All rights reserved.

Trypanosoma cruzi MSH2: Functional analyses on different parasite strains provide evidences for a role on the oxidative stress response

Components of the DNA mismatch repair (MMR) pathway are major players in processes known to generate genetic diversity, such as mutagenesis and DNA recombination. Trypanosoma cruzi, the protozoan parasite that causes Chagas disease has a highly heterogeneous population, composed of a pool of strains with distinct characteristics. Studies with a number of molecular markers identified up to six groups in the T. cruzi population, which showed distinct levels of genetic variability. To investigate the molecular basis for such differences, we analyzed the T. cruzi MSH2 gene, which encodes a key component of MMR, and showed the existence of distinct isoforms of this protein. Here we compared cell survival rates after exposure to genotoxic agents and levels of oxidative stress-induced DNA in different parasite strains. Analyses of msh2 mutants in both T. cruzi and T. brucei were also used to investigate the role of Tcmsh2 in the response to various DNA damaging agents. The results suggest that the distinct MSH2 isoforms have differences in their activity. More importantly, they also indicate that, in addition to its role in MMR, TcMSH2 acts in the parasite response to oxidative stress through a novel mitochondrial function that may be conserved in T. brucei. (C) 2010 Elsevier B.V. All rights reserved.

Melatonin triggers PKA activation in the rodent malaria parasite Plasmodium chabaudi

Calcium (Ca2+) is a critical regulator of many aspects of the Plasmodium reproductive cycle. In particular, intra-erythrocyte Plasmodium parasites respond to circulating levels of the melatonin in a process mediated partly by intracellular Ca2+. Melatonin promotes the development and synchronicity of parasites, thereby enhancing their spread and worsening the clinical implications. The signalling mechanisms underlying the effects of melatonin are not fully established, although both Ca2+ and cyclic AMP (cAMP) have been implicated. Furthermore, it is not clear whether different strains of Plasmodium use the same, or divergent, signals to control their development. The aim of this study was to explore the signalling mechanisms engaged by melatonin in P. chabaudi, a virulent rodent parasite. Using parasites at the throphozoite stage acutely isolated from mice erythrocytes, we demonstrate that melatonin triggers cAMP production and protein kinase A (PKA) activation. Interestingly, the stimulation of cAMP/PKA signalling by melatonin was dependent on elevation of Ca2+ within the parasite, because buffering Ca2+ changes using the chelator BAPTA prevented cAMP production in response to melatonin. Incubation with melatonin evoked robust Ca2+ signals within the parasite, as did the application of a membrane-permeant analogue of cAMP. Our data suggest that P. chabaudi engages both Ca2+ and cAMP signalling systems when stimulated by melatonin. Furthermore, there is positive feedback between these messengers, because Ca2+ evokes cAMP elevation and vice versa. Melatonin more than doubled the observed extent of parasitemia, and the increase in cAMP concentration and PKA activation was essential for this effect. These data support the possibility to use melatonin antagonists or derivates in therapeutic approach.