Biomedical subjects
Publications and source records attributed to Sophie Goyard.
Five isoforms of protein mannosyltransferase (Pmt) O-mannosylate secretory proteins in Candida albicans. pmt mutants were differentially defective for biofilm formation on plastic in static and flow-through systems, and a Pmt inhibitor blocked early stages of biofilm formation. Conceptually, Pmt inhibition may prevent surface anchoring and biofilm-dependent resistance of fungal pathogens.
Leishmania donovani are the causative agents of kala-azar in humans. They undergo a developmental program following changes in the environment, resulting in the reversible transformation between the extracellular promastigote form in the sand fly vector and the obligatory intracellular amastigote form in phagolysosomes of macrophages. A host-free differentiation system for L. donovani was used to investigate the initial process of promastigote to amastigote differentiation. Within an hour after exposing promastigotes to differentiation signal (concomitant exposure to 37 degrees C and pH 5.5), they expressed the amastigote-specific A2 protein family. At 5 h they started to transform to amastigote-shaped cells, a process that was completed 7 h later. This morphological transformation occurred synchronously, while cells arrested at G1. By sequential exposure to elevated temperature (for 24 h) and then acidic pH, we found that heat was responsible for the growth arrest and acidic pH to its release and subsequent route to differentiation into amastigotes. Lastly, ethanol and Azetidine 2 carboxylic acid (a synthetic proline analog) that induced heat shock response in promastigotes were capable of replacing heat in the differentiation signal.
Phospholipases play an important role as virulence factors in human pathogens. Candida albicans, the major fungal pathogen of humans, encodes phospholipases of type A, B, C and D. Type B Plb2 and type D Pld1 phospholipases have been shown to contribute to virulence in this organism. We analyzed, in C. albicans, PLC2 and PLC3, two highly conserved genes coding for phosphatidylinositol-dependent phospholipases C with homology to the known virulence factor PlcA in the human pathogen Listeria monocytogenes. We show that expression of PLC2 and PLC3 is upregulated under different filament-inducing conditions and in the constitutive filamentous mutant tup1Delta. In order to analyze PLC2 and PLC3 function in C. albicans, we constructed strains that carry PLC2 or PLC3 under a constitutive promoter and strains that lack all four PLC2/3 alleles. These strains were not affected in their ability to produce filaments under non-inducing conditions, nor was filamentation modified under inducing conditions, suggesting that PLC2/3 are not critical determinants of the yeast-to-hypha switch. In a cell culture model for macrophage interaction, phagocytosis of C. albicans and subsequent killing were not influenced by PLC2/3. These results demonstrate that C. albicans PLC2 and PLC3 are dispensable for virulence; moreover, they underline the sharp contrast with the function of plcA in L. monocytogenes.
In this study, we have established conditions for generating Leishmania amazonensis recombinants stably expressing the firefly luciferase gene. These parasites produced significant bioluminescent signals for both in vitro studies and the development of an in vivo model, allowing the course of the parasitism to be readily monitored in real time in the living animals such as laboratory mice. First, a model was established, using parasite-infected mouse macrophages for rapidly determining the activity of drugs against intracellular amastigotes. Results indicated that recombinant Leishmania can be reliably and confidently used to monitor compounds acting on intracellular amastigote-harbouring macrophages. Secondly, temporal analyses were performed following inoculation of metacyclic promastigotes into the ear dermis of BALB/c mice and the bioluminescent light transmitted through the tissue was imaged externally using a charge coupled device (CCD) camera. Bioluminescent signals, measured at the inoculation site and in the draining lymph node of mice containing these parasites correlated well with the more classical quantification of parasites. These assays prove that the real-time bioluminescent assay is not only sensitive but also more rapid than culture-base techniques allowing to monitor parasite-load before any clinical signs of leishmaniasis are detectable. In short, this luciferase imaging study is useful to monitor the efficacy of anti-leishmanial drugs on live cell culture and to trace leishmanial infection in animal models.
Advances in our understanding of the protozoan parasite Leishmania have been facilitated by the development of molecular and genetic tools. One powerful approach for gene identification and analysis is transposon mutagenesis. This can be performed directly in vivo, but often it is more convenient to generate transpositions in vitro for subsequent analysis in vivo, in a process termed "shuttle mutagenesis." The Drosophila element mariner is well suited for application by either route. Minimal mariner elements containing cis-acting elements required for transposition have been generated, which can be further modified to suit the needs of the experimenter. Additional genetic markers and/or reporters can be introduced, which are useful for procedures such as insertional mutagenesis, shotgun sequencing, or the generation of protein and transcriptional fusions for subsequent analysis. Active transposase can readily be generated following expression in Escherichia coli, and efficiencies of 10-3/target can be obtained, allow-ing the generation of large transposon insertion libraries suitable for subsequent screening in vivo. This chapter explains the steps necessary to purify active Mos1 transposase and conduct an in vitro transposition reaction. We also discuss some of the considerations relevant to the design and application of functional mariner elements (donor plasmids) relevant to studies in Leishmania and other organisms.
Glycoconjugates have been shown to play important roles in Leishmania development. However, the ability to study these molecules and other processes would benefit greatly from improved methods for genetic manipulation and analysis of the amastigote stage. This is especially challenging for L. donovani, the agent of the most severe form of leishmaniasis, which can rapidly lose virulence during in vitro culture. Here we report on a clonal subline of an L. donovani 1S2D (LdBob or LdB), which differentiates readily from promastigotes to amastigotes in axenic culture, and maintains this ability during extended parasite cultivation in vitro. This derivative can be plated and transfected efficiently while grown as promastigotes or amastigotes. Importantly, LdB maintains the ability to differentiate while undergoing genetic alterations required for creation of gene knockouts and complemented lines. Like virulent L. donovani, LdB exhibits down-regulation of lipophosphoglycan (LPG) synthesis and up-regulation of A2 protein synthesis in amastigotes. We showed that knockouts of LPG2, encoding a Golgi GDP-mannose transporter, eliminated phosphoglycan synthesis in LdB axenic amastigotes. These and other data suggest that LdB axenic amastigotes will be generally useful as a differentiation model in studies of gene expression, virulence, glycoconjugate function and drug susceptibility in L. donovani.
Leishmania are important protozoan pathogens of humans in temperate and tropical regions. The study of gene expression during the infectious cycle, in mutants or after environmental or chemical stimuli, is a powerful approach towards understanding parasite virulence and the development of control measures. Like other trypanosomatids, Leishmania gene expression is mediated by a polycistronic transcriptional process that places increased emphasis on post-transcriptional regulatory mechanisms including RNA processing and protein translation. With the impending completion of the Leishmania genome, global approaches surveying mRNA and protein expression are now feasible. Our laboratory has developed the Drosophila transposon mariner as a tool for trapping Leishmania genes and studying their regulation in the form of protein fusions; a classic approach in other microbes that can be termed 'proteogenomics'. Similarly, we have developed reagents and approaches for the creation of DNA microarrays, which permit the measurement of RNA abundance across the parasite genome. Progress in these areas promises to greatly increase our understanding of global mechanisms of gene regulation at both mRNA and protein levels, and to lead to the identification of many candidate genes involved in virulence.