DNA polymerase beta mRNA determination by relative quantitative RT-PCR from Leishmania infantum intracellular amastigotes

Gene expression level is extremely difficult to assess in the intracellular form of Leishmania infantum, the amastigote, due to host mRNA contamination, low supply of parasites and stress degradation problems. We obtained and analyzed L. infantum DNA polymerase beta (Li Pol beta), a suitable enzyme for differential expression studies. The amount of Li Pol beta mRNA was determined in different forms of the parasite (extracellular promastigote, intracellular amastigote) by Northern blot and by relative quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Amastigote transcript levels were determined from both gradient-purified parasites and directly from a population of infected macrophages. The mRNA, undetectable when obtained from amastigotes by the classic gradient centrifugation method and subsequent Northern analysis, was clearly and specifically detectable by this quantitative RT-PCR method from the mixed macrophage/parasite cell population. Li Pol beta displays a different pattern of expression in the distinct forms of the parasite cycle that correlate with the infectivity of the protozoon. Thus, Li Pol beta mRNA expression is developmentally regulated, being clearly higher in the more infective forms of the parasite.

S-adenosylmethionine decarboxylase from Leishmania infantum promastigotes: molecular cloning and differential expression

S-Adenosylmethionine decarboxylase (AdoMetDC), an enzyme involved in the synthesis of polyamines as well as in the cell methylation processes, has been considered in trypanosomes as a specific drug target. We have cloned by RT-PCR a DNA fragment of 1,364 bp which contains the open reading frame and the 5' end fragment of the AdoMetDC encoding gene from the parasite protozoon Leishmania infantum. The 1,197 bp ORF encodes for a 392 amino acid residue polypeptide. The sequence comparison with AdMetDC from different species showed a high level of homology, around 80%. with the American and African trypanosomes and a certain distance from the polypeptides of higher eukaryotes. AdoMetDC has been cloned in a pQE32 vector and overexpressed in a M15 Escherichia coli strain. The gene expression shows variations between the distinct phases of the parasite, being higher in the most infective one. This fact may be related to the multiple defense mechanism of the protozoon against the macrophage action.

Nuclear DNA polymerase beta from Leishmania infantum. Cloning, molecular analysis and developmental regulation

We have identified a novel polymerase beta (Pol beta)-like enzyme from Leishmania infantum, a parasite protozoon causing disease in humans. This protein, named Li Pol beta, shows a nuclear localization that contrasts with the mitochondrial localization of Pol beta from Crithidia fasciculata, a closely related parasite, the only polymerase beta described so far in Trypanosomatidae. Li Pol beta, that belongs to the DNA polymerase X family, displays an evolutionarily conserved Pol beta-type DNA polymerase core, in which most of the key residues involved in DNA binding, nucleotide binding, dRPase and polymerization catalysis are conserved. In agreement with this, Li Pol beta, overproduced in Escherichia coli, displayed intrinsic DNA polymerase activity. Cell synchronization experiments showed a correlation between both Li Pol beta mRNA and protein levels along the parasite cell cycle. Analysis of these parameters at the different growth phases of the parasite, from the proliferative (non-infective) logarithmic phase to the non-dividing (highly infectious) stationary phase, showed high levels of Li Pol beta at the infective phase of the parasite. The data suggest a role of Li Pol beta in base excision repair in L.infantum, a parasite usually affected by oxygen stress environments into the macrophage host cells.

Ependymal reaction after experimental spinal cord injury

Images of ependymal cell proliferation after experimental spinal cord injury in the rabbit are presented. This finding suggests that segmental central canal obliteration after injury could be considered in the pathogenesis of posttraumatic syringomyelia.