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1.  Differences in Gene Transcriptomic Pattern of Plasmodium falciparum in Children with Cerebral Malaria and Asymptomatic Carriers 
PLoS ONE  2014;9(12):e114401.
The mechanisms underlying the heterogeneity of clinical malaria remain largely unknown. We hypothesized that differential gene expression contributes to phenotypic variation of parasites which results in a specific interaction with the host, leading to different clinical features of malaria. In this study, we analyzed the transcriptomes of isolates obtained from asymptomatic carriers and patients with uncomplicated or cerebral malaria. We also investigated the transcriptomes of 3D7 clone and 3D7-Lib that expresses severe malaria associated-variant surface antigen. Our findings revealed a specific up-regulation of genes involved in pathogenesis, adhesion to host cell, and erythrocyte aggregation in parasites from patients with cerebral malaria and 3D7-Lib, compared to parasites from asymptomatic carriers and 3D7, respectively. However, we did not find any significant difference between the transcriptomes of parasites from cerebral malaria and uncomplicated malaria, suggesting similar transcriptomic pattern in these two parasite populations. The difference between isolates from asymptomatic children and cerebral malaria concerned genes coding for exported proteins, Maurer's cleft proteins, transcriptional factor proteins, proteins implicated in protein transport, as well as Plasmodium conserved and hypothetical proteins. Interestingly, UPs A1, A2, A3 and UPs B1 of var genes were predominantly found in cerebral malaria-associated isolates and those containing architectural domains of DC4, DC5, DC13 and their neighboring rif genes in 3D7-lib. Therefore, more investigations are needed to analyze the effective role of these genes during malaria infection to provide with new knowledge on malaria pathology. In addition, concomitant regulation of genes within the chromosomal neighborhood suggests a common mechanism of gene regulation in P. falciparum.
doi:10.1371/journal.pone.0114401
PMCID: PMC4257676  PMID: 25479608
2.  A Putative Regulatory Genetic Locus Modulates Virulence in the Pathogen Leptospira interrogans 
Infection and Immunity  2014;82(6):2542-2552.
Limited research has been conducted on the role of transcriptional regulators in relation to virulence in Leptospira interrogans, the etiological agent of leptospirosis. Here, we identify an L. interrogans locus that encodes a sensor protein, an anti-sigma factor antagonist, and two genes encoding proteins of unknown function. Transposon insertion into the gene encoding the sensor protein led to dampened transcription of the other 3 genes in this locus. This lb139 insertion mutant (the lb139− mutant) displayed attenuated virulence in the hamster model of infection and reduced motility in vitro. Whole-transcriptome analyses using RNA sequencing revealed the downregulation of 115 genes and the upregulation of 28 genes, with an overrepresentation of gene products functioning in motility and signal transduction and numerous gene products with unknown functions, predicted to be localized to the extracellular space. Another significant finding encompassed suppressed expression of the majority of the genes previously demonstrated to be upregulated at physiological osmolarity, including the sphingomyelinase C precursor Sph2 and LigB. We provide insight into a possible requirement for transcriptional regulation as it relates to leptospiral virulence and suggest various biological processes that are affected due to the loss of native expression of this genetic locus.
doi:10.1128/IAI.01803-14
PMCID: PMC4019197  PMID: 24686063
3.  Identification of RNA partners of viral proteins in infected cells 
RNA Biology  2013;10(6):943-956.
RNA viruses exhibit small-sized genomes encoding few proteins, but still establish complex networks of protein-protein and RNA-protein interactions within a cell to achieve efficient replication and spreading. Deciphering these interactions is essential to reach a comprehensive understanding of the viral infection process. To study RNA-protein complexes directly in infected cells, we developed a new approach based on recombinant viruses expressing tagged viral proteins that were purified together with their specific RNA partners. High-throughput sequencing was then used to identify these RNA molecules. As a proof of principle, this method was applied to measles virus nucleoprotein (MV-N). It revealed that in addition to full-length genomes, MV-N specifically interacted with a unique population of 5′ copy-back defective interfering RNA genomes that we characterized. Such RNA molecules were able to induce strong activation of interferon-stimulated response element promoter preferentially via the cytoplasmic pattern recognition receptor RIG-I protein, demonstrating their biological functionality. Thus, this method provides a new platform to explore biologically active RNA-protein networks that viruses establish within infected cells.
doi:10.4161/rna.24453
PMCID: PMC4111734  PMID: 23595062
RNA-protein interactions; next-generation sequencing; affinity purification; tagged proteins; measles virus; nucleocapsids
4.  Expanding the RpoS/σS-Network by RNA Sequencing and Identification of σS-Controlled Small RNAs in Salmonella 
PLoS ONE  2014;9(5):e96918.
The RpoS/σS sigma subunit of RNA polymerase (RNAP) controls a global adaptive response that allows many Gram-negative bacteria to survive starvation and various stresses. σS also contributes to biofilm formation and virulence of the food-borne pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium). In this study, we used directional RNA-sequencing and complementary assays to explore the σS-dependent transcriptome of S. Typhimurium during late stationary phase in rich medium. This study confirms the large regulatory scope of σS and provides insights into the physiological functions of σS in Salmonella. Extensive regulation by σS of genes involved in metabolism and membrane composition, and down-regulation of the respiratory chain functions, were important features of the σS effects on gene transcription that might confer fitness advantages to bacterial cells and/or populations under starving conditions. As an example, we show that arginine catabolism confers a competitive fitness advantage in stationary phase. This study also provides a firm basis for future studies to address molecular mechanisms of indirect regulation of gene expression by σS. Importantly, the σS-controlled downstream network includes small RNAs that might endow σS with post-transcriptional regulatory functions. Of these, four (RyhB-1/RyhB-2, SdsR, SraL) were known to be controlled by σS and deletion of the sdsR locus had a competitive fitness cost in stationary phase. The σS-dependent control of seven additional sRNAs was confirmed in Northern experiments. These findings will inspire future studies to investigate molecular mechanisms and the physiological impact of post-transcriptional regulation by σS.
doi:10.1371/journal.pone.0096918
PMCID: PMC4014581  PMID: 24810289
5.  Identification of the Virulence Landscape Essential for Entamoeba histolytica Invasion of the Human Colon 
PLoS Pathogens  2013;9(12):e1003824.
Entamoeba histolytica is the pathogenic amoeba responsible for amoebiasis, an infectious disease targeting human tissues. Amoebiasis arises when virulent trophozoites start to destroy the muco-epithelial barrier by first crossing the mucus, then killing host cells, triggering inflammation and subsequently causing dysentery. The main goal of this study was to analyse pathophysiology and gene expression changes related to virulent (i.e. HM1:IMSS) and non-virulent (i.e. Rahman) strains when they are in contact with the human colon. Transcriptome comparisons between the two strains, both in culture conditions and upon contact with human colon explants, provide a global view of gene expression changes that might contribute to the observed phenotypic differences. The most remarkable feature of the virulent phenotype resides in the up-regulation of genes implicated in carbohydrate metabolism and processing of glycosylated residues. Consequently, inhibition of gene expression by RNA interference of a glycoside hydrolase (β-amylase absent from humans) abolishes mucus depletion and tissue invasion by HM1:IMSS. In summary, our data suggest a potential role of carbohydrate metabolism in colon invasion by virulent E. histolytica.
Author Summary
Entamoeba histolytica is an intestinal parasite which displays diverse phenotypes with respect to pathogenesis in the human colon. Trophozoites can remain as commensal, without causing evident intestinal damage, or they can destroy the colonic mucosa leading to amoebiasis. Using human colon explants and transcriptome analysis, we investigated the gene expression profile of two E. histolytica strains (virulent and non-virulent) during their contact with the intestinal mucus to gain insights into the molecular basis responsible for amoebic divergent phenotypes. Our results suggest that the virulent E. histolytica, when in contact with the intestinal barrier, specifically increases the rate of gene transcription for enzymes necessary to exploits the carbohydrate resources present in the human colon. Using RNA interference methodologies to knockdown gene expression, our data revealed the potential role of amoebic β-amylase (a glycosydase) in colon invasion and mucus depletion. Our data implies that the ability of an E. histolytica strain to exploit the carbohydrate resources might affect its ability to invasion the intestine.
doi:10.1371/journal.ppat.1003824
PMCID: PMC3868522  PMID: 24385905
6.  Life in an Arsenic-Containing Gold Mine: Genome and Physiology of the Autotrophic Arsenite-Oxidizing Bacterium Rhizobium sp. NT-26 
Genome Biology and Evolution  2013;5(5):934-953.
Arsenic is widespread in the environment and its presence is a result of natural or anthropogenic activities. Microbes have developed different mechanisms to deal with toxic compounds such as arsenic and this is to resist or metabolize the compound. Here, we present the first reference set of genomic, transcriptomic and proteomic data of an Alphaproteobacterium isolated from an arsenic-containing goldmine: Rhizobium sp. NT-26. Although phylogenetically related to the plant-associated bacteria, this organism has lost the major colonizing capabilities needed for symbiosis with legumes. In contrast, the genome of Rhizobium sp. NT-26 comprises a megaplasmid containing the various genes, which enable it to metabolize arsenite. Remarkably, although the genes required for arsenite oxidation and flagellar motility/biofilm formation are carried by the megaplasmid and the chromosome, respectively, a coordinate regulation of these two mechanisms was observed. Taken together, these processes illustrate the impact environmental pressure can have on the evolution of bacterial genomes, improving the fitness of bacterial strains by the acquisition of novel functions.
doi:10.1093/gbe/evt061
PMCID: PMC3673622  PMID: 23589360
arsenic metabolism; motility/biofilm; Rhizobium/Agrobacterium; transcriptomics/proteomics; phylogeny; rhizosphere
7.  Docosahexaenoic Acid Inhibits Helicobacter pylori Growth In Vitro and Mice Gastric Mucosa Colonization 
PLoS ONE  2012;7(4):e35072.
H. pylori drug-resistant strains and non-compliance to therapy are the major causes of H. pylori eradication failure. For some bacterial species it has been demonstrated that fatty acids have a growth inhibitory effect. Our main aim was to assess the ability of docosahexaenoic acid (DHA) to inhibit H. pylori growth both in vitro and in a mouse model. The effectiveness of standard therapy (ST) in combination with DHA on H. pylori eradication and recurrence prevention success was also investigated. The effects of DHA on H. pylori growth were analyzed in an in vitro dose-response study and n in vivo model. We analized the ability of H. pylori to colonize mice gastric mucosa following DHA, ST or a combination of both treatments. Our data demonstrate that DHA decreases H. pylori growth in vitro in a dose-dependent manner. Furthermore, DHA inhibits H. pylori gastric colonization in vivo as well as decreases mouse gastric mucosa inflammation. Addition of DHA to ST was also associated with lower H. pylori infection recurrence in the mouse model. In conclusion, DHA is an inhibitor of H. pylori growth and its ability to colonize mouse stomach. DHA treatment is also associated with a lower recurrence of H. pylori infection in combination with ST. These observations pave the way to consider DHA as an adjunct agent in H. pylori eradication treatment.
doi:10.1371/journal.pone.0035072
PMCID: PMC3328494  PMID: 22529974
8.  Endoplasmic Reticulum Stress-Sensing Mechanism Is Activated in Entamoeba histolytica upon Treatment with Nitric Oxide 
PLoS ONE  2012;7(2):e31777.
The Endoplasmic Reticulum stores calcium and is a site of protein synthesis and modification. Changes in ER homeostasis lead to stress responses with an activation of the unfolded protein response (UPR). The Entamoeba histolytica endomembrane system is simple compared to those of higher eukaryotes, as a canonical ER is not observed. During amoebiasis, an infection of the human intestine and liver by E. histolytica, nitric oxide (NO) triggers an apoptotic-like event preceded by an impairment of energy production and a loss of important parasite pathogenic features. We address the question of how this ancient eukaryote responds to stress induced by immune components (i.e. NO) and whether stress leads to ER changes and subsequently to an UPR. Gene expression analysis suggested that NO triggers stress responses marked by (i) dramatic up-regulation of hsp genes although a bona fide UPR is absent; (ii) induction of DNA repair and redox gene expression and iii) up-regulation of glycolysis-related gene expression. Enzymology approaches demonstrate that NO directly inhibits glycolysis and enhance cysteine synthase activity. Using live imaging and confocal microscopy we found that NO dramatically provokes extensive ER fragmentation. ER fission in E. histolytica appears as a protective response against stress, as it has been recently proposed for neuron self-defense during neurologic disorders. Chronic ER stress is also involved in metabolic diseases including diabetes, where NO production reduces ER calcium levels and activates cell death. Our data highlighted unique cellular responses of interest to understand the mechanisms of parasite death during amoebiasis.
doi:10.1371/journal.pone.0031777
PMCID: PMC3286455  PMID: 22384074
9.  Temporal transcriptomic response during arsenic stress in Herminiimonas arsenicoxydans 
BMC Genomics  2010;11:709.
Background
Arsenic is present in numerous ecosystems and microorganisms have developed various mechanisms to live in such hostile environments. Herminiimonas arsenicoxydans, a bacterium isolated from arsenic contaminated sludge, has acquired remarkable capabilities to cope with arsenic. In particular our previous studies have suggested the existence of a temporal induction of arsenite oxidase, a key enzyme in arsenic metabolism, in the presence of As(III).
Results
Microarrays were designed to compare gene transcription profiles under a temporal As(III) exposure. Transcriptome kinetic analysis demonstrated the existence of two phases in arsenic response. The expression of approximatively 14% of the whole genome was significantly affected by an As(III) early stress and 4% by an As(III) late exposure. The early response was characterized by arsenic resistance, oxidative stress, chaperone synthesis and sulfur metabolism. The late response was characterized by arsenic metabolism and associated mechanisms such as phosphate transport and motility. The major metabolic changes were confirmed by chemical, transcriptional, physiological and biochemical experiments. These early and late responses were defined as general stress response and specific response to As(III), respectively.
Conclusion
Gene expression patterns suggest that the exposure to As(III) induces an acute response to rapidly minimize the immediate effects of As(III). Upon a longer arsenic exposure, a broad metabolic response was induced. These data allowed to propose for the first time a kinetic model of the As(III) response in bacteria.
doi:10.1186/1471-2164-11-709
PMCID: PMC3022917  PMID: 21167028
10.  From array-based hybridization of Helicobacter pylori isolates to the complete genome sequence of an isolate associated with MALT lymphoma 
BMC Genomics  2010;11:368.
Background
elicobacter pylori infection is associated with several gastro-duodenal inflammatory diseases of various levels of severity. To determine whether certain combinations of genetic markers can be used to predict the clinical source of the infection, we analyzed well documented and geographically homogenous clinical isolates using a comparative genomics approach.
Results
A set of 254 H. pylori genes was used to perform array-based comparative genomic hybridization among 120 French H. pylori strains associated with chronic gastritis (n = 33), duodenal ulcers (n = 27), intestinal metaplasia (n = 17) or gastric extra-nodal marginal zone B-cell MALT lymphoma (n = 43). Hierarchical cluster analyses of the DNA hybridization values allowed us to identify a homogeneous subpopulation of strains that clustered exclusively with cagPAI minus MALT lymphoma isolates. The genome sequence of B38, a representative of this MALT lymphoma strain-cluster, was completed, fully annotated, and compared with the six previously released H. pylori genomes (i.e. J99, 26695, HPAG1, P12, G27 and Shi470). B38 has the smallest H. pylori genome described thus far (1,576,758 base pairs containing 1,528 CDSs); it contains the vacAs2m2 allele and lacks the genes encoding the major virulence factors (absence of cagPAI, babB, babC, sabB, and homB). Comparative genomics led to the identification of very few sequences that are unique to the B38 strain (9 intact CDSs and 7 pseudogenes). Pair-wise genomic synteny comparisons between B38 and the 6 H. pylori sequenced genomes revealed an almost complete co-linearity, never seen before between the genomes of strain Shi470 (a Peruvian isolate) and B38.
Conclusion
These isolates are deprived of the main H. pylori virulence factors characterized previously, but are nonetheless associated with gastric neoplasia.
doi:10.1186/1471-2164-11-368
PMCID: PMC3091627  PMID: 20537153
11.  The Global Regulator CodY Regulates Toxin Gene Expression in Bacillus anthracis and Is Required for Full Virulence▿ †  
Infection and Immunity  2009;77(10):4437-4445.
In gram-positive bacteria, CodY is an important regulator of genes whose expression changes upon nutrient limitation and acts as a repressor of virulence gene expression in some pathogenic species. Here, we report the role of CodY in Bacillus anthracis, the etiologic agent of anthrax. Disruption of codY completely abolished virulence in a toxinogenic, noncapsulated strain, indicating that the activity of CodY is required for full virulence of B. anthracis. Global transcriptome analysis of a codY mutant and the parental strain revealed extensive differences. These differences could reflect direct control for some genes, as suggested by the presence of CodY binding sequences in their promoter regions, or indirect effects via the CodY-dependent control of other regulatory proteins or metabolic rearrangements in the codY mutant strain. The differences included reduced expression of the anthrax toxin genes in the mutant strain, which was confirmed by lacZ reporter fusions and immunoblotting. The accumulation of the global virulence regulator AtxA protein was strongly reduced in the mutant strain. However, in agreement with the microarray data, expression of atxA, as measured using an atxA-lacZ transcriptional fusion and by assaying atxA mRNA, was not significantly affected in the codY mutant. An atxA-lacZ translational fusion was also unaffected. Overexpression of atxA restored toxin component synthesis in the codY mutant strain. These results suggest that CodY controls toxin gene expression by regulating AtxA accumulation posttranslationally.
doi:10.1128/IAI.00716-09
PMCID: PMC2747959  PMID: 19651859
12.  Multiple controls affect arsenite oxidase gene expression in Herminiimonas arsenicoxydans 
BMC Microbiology  2010;10:53.
Background
Both the speciation and toxicity of arsenic are affected by bacterial transformations, i.e. oxidation, reduction or methylation. These transformations have a major impact on environmental contamination and more particularly on arsenic contamination of drinking water. Herminiimonas arsenicoxydans has been isolated from an arsenic- contaminated environment and has developed various mechanisms for coping with arsenic, including the oxidation of As(III) to As(V) as a detoxification mechanism.
Results
In the present study, a differential transcriptome analysis was used to identify genes, including arsenite oxidase encoding genes, involved in the response of H. arsenicoxydans to As(III). To get insight into the molecular mechanisms of this enzyme activity, a Tn5 transposon mutagenesis was performed. Transposon insertions resulting in a lack of arsenite oxidase activity disrupted aoxR and aoxS genes, showing that the aox operon transcription is regulated by the AoxRS two-component system. Remarkably, transposon insertions were also identified in rpoN coding for the alternative N sigma factor (σ54) of RNA polymerase and in dnaJ coding for the Hsp70 co-chaperone. Western blotting with anti-AoxB antibodies and quantitative RT-PCR experiments allowed us to demonstrate that the rpoN and dnaJ gene products are involved in the control of arsenite oxidase gene expression. Finally, the transcriptional start site of the aoxAB operon was determined using rapid amplification of cDNA ends (RACE) and a putative -12/-24 σ54-dependent promoter motif was identified upstream of aoxAB coding sequences.
Conclusion
These results reveal the existence of novel molecular regulatory processes governing arsenite oxidase expression in H. arsenicoxydans. These data are summarized in a model that functionally integrates arsenite oxidation in the adaptive response to As(III) in this microorganism.
doi:10.1186/1471-2180-10-53
PMCID: PMC2848651  PMID: 20167112
13.  Nonpathogenic SIV infection of African green monkeys induces a strong but rapidly controlled type I IFN response 
The Journal of Clinical Investigation  2009;119(12):3544-3555.
African green monkeys (AGMs) infected with the AGM type of SIV (SIVagm) do not develop chronic immune activation and AIDS, despite viral loads similar to those detected in humans infected with HIV-1 and rhesus macaques (RMs) infected with the RM type of SIV (SIVmac). Because chronic immune activation drives progressive CD4+ T cell depletion and immune cell dysfunctions, factors that characterize disease progression, we sought to understand the molecular basis of this AGM phenotype. To this end, we longitudinally assessed the gene expression profiles of blood- and lymph node–derived CD4+ cells from AGMs and RMs in response to SIVagm and SIVmac infection, respectively, using a genomic microarray platform. The molecular signature of acute infection was characterized, in both species, by strong upregulation of type I IFN–stimulated genes (ISGs). ISG expression returned to basal levels after postinfection day 28 in AGMs but was sustained in RMs, especially in the lymph node–derived cells. We also found that SIVagm induced IFN-α production by AGM cells in vitro and that low IFN-α levels were sufficient to induce strong ISG responses. In conclusion, SIV infection triggered a rapid and strong IFN-α response in vivo in both AGMs and RMs, with this response being efficiently controlled only in AGMs, possibly as a result of active regulatory mechanisms.
doi:10.1172/JCI40093
PMCID: PMC2786805  PMID: 19959873
14.  FlexiChip package: an universal microarray with a dedicated analysis software for high-thoughput SNPs detection linked to anti-malarial drug resistance 
Malaria Journal  2009;8:229.
Background
A number of molecular tools have been developed to monitor the emergence and spread of anti-malarial drug resistance to Plasmodium falciparum. One of the major obstacles to the wider implementation of these tools is the absence of practical methods enabling high throughput analysis. Here a new Zip-code array is described, called FlexiChip, linked to a dedicated software program, which largely overcomes this problem.
Methods
Previously published microarray probes detecting single-nucleotide polymorphisms (SNP) associated with parasite resistance to anti-malarial drugs (ResMalChip) were adapted for a universal microarray FlexiChip format. To evaluate the overall sensitivity of the FlexiChip package (microarray + software), the results of FlexiChip were compared to ResMalChip microarray, using the same extension probes and with the same PCR products. In both cases, sequence results were used as gold standard to calculate sensitivity and specificity. FlexiChip results obtained with a set of field isolates were then compared to those assessed in an independent reference laboratory.
Results
The FlexiChip package gave results identical to the ResMalChip results in 92.7% of samples (kappa coefficient 0.8491, with a standard error 0.021) and had a sensitivity of 95.88% and a specificity of 97.68% compared to the sequencing as the reference method. Moreover the method performed well compared to the results obtained in the reference laboratories, with 99.7% of identical results (kappa coefficient 0.9923, S.E. 0.0523).
Conclusion
Microarrays could be employed to monitor P. falciparum drug resistance markers with greater cost effectiveness and the possibility for high throughput analysis. The FlexiChip package is a promising tool for use in poor resource settings of malaria endemic countries.
doi:10.1186/1475-2875-8-229
PMCID: PMC2770542  PMID: 19828052
16.  Growth of Yersinia pseudotuberculosis in human plasma: impacts on virulence and metabolic gene expression 
BMC Microbiology  2008;8:211.
Background
In man, infection by the Gram-negative enteropathogen Yersinia pseudotuberculosis is usually limited to the terminal ileum. However, in immunocompromised patients, the microorganism may disseminate from the digestive tract and thus cause a systemic infection with septicemia.
Results
To gain insight into the metabolic pathways and virulence factors expressed by the bacterium at the blood stage of pseudotuberculosis, we compared the overall gene transcription patterns (the transcriptome) of bacterial cells cultured in either human plasma or Luria-Bertani medium. The most marked plasma-triggered metabolic consequence in Y. pseudotuberculosis was the switch to high glucose consumption, which is reminiscent of the acetogenic pathway (known as "glucose overflow") in Escherichia coli. However, upregulation of the glyoxylate shunt enzymes suggests that (in contrast to E. coli) acetate may be further metabolized in Y. pseudotuberculosis. Our data also indicate that the bloodstream environment can regulate major virulence genes (positively or negatively); the yadA adhesin gene and most of the transcriptional units of the pYV-encoded type III secretion apparatus were found to be upregulated, whereas transcription of the pH6 antigen locus was strongly repressed.
Conclusion
Our results suggest that plasma growth of Y. pseudotuberculosis is responsible for major transcriptional regulatory events and prompts key metabolic reorientations within the bacterium, which may in turn have an impact on virulence.
doi:10.1186/1471-2180-8-211
PMCID: PMC2631605  PMID: 19055764
17.  Dynamic RNA profiling in Plasmodium falciparum synchronized blood stages exposed to lethal doses of artesunate 
BMC Genomics  2008;9:388.
Background
Translation of the genome sequence of Plasmodium sp. into biologically relevant information relies on high through-put genomics technology which includes transcriptome analysis. However, few studies to date have used this powerful approach to explore transcriptome alterations of P. falciparum parasites exposed to antimalarial drugs.
Results
The rapid action of artesunate allowed us to study dynamic changes of the parasite transcriptome in synchronous parasite cultures exposed to the drug for 90 minutes and 3 hours. Developmentally regulated genes were filtered out, leaving 398 genes which presented altered transcript levels reflecting drug-exposure. Few genes related to metabolic pathways, most encoded chaperones, transporters, kinases, Zn-finger proteins, transcription activating proteins, proteins involved in proteasome degradation, in oxidative stress and in cell cycle regulation. A positive bias was observed for over-expressed genes presenting a subtelomeric location, allelic polymorphism and encoding proteins with potential export sequences, which often belonged to subtelomeric multi-gene families. This pointed to the mobilization of processes shaping the interface between the parasite and its environment. In parallel, pathways were engaged which could lead to parasite death, such as interference with purine/pyrimidine metabolism, the mitochondrial electron transport chain, proteasome-dependent protein degradation or the integrity of the food vacuole.
Conclusion
The high proportion of over-expressed genes encoding proteins exported from the parasite highlight the importance of extra-parasitic compartments as fields for exploration in drug research which, to date, has mostly focused on the parasite itself rather than on its intra and extra erythrocytic environment. Further work is needed to clarify which transcriptome alterations observed reflect a specific response to overcome artesunate toxicity or more general perturbations on the path to cellular death.
doi:10.1186/1471-2164-9-388
PMCID: PMC2536677  PMID: 18706115
18.  Transcriptome analysis of antigenic variation in Plasmodium falciparum - var silencing is not dependent on antisense RNA 
Genome Biology  2005;6(11):R93.
A microarray analysis of Plasmodium falciparum selected to express different var genes suggests that antisense transcripts are not responsible for the transcriptional silencing of non-expressed var genes.
Background
Plasmodium falciparum, the causative agent of the most severe form of malaria, undergoes antigenic variation through successive presentation of a family of antigens on the surface of parasitized erythrocytes. These antigens, known as Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins, are subject to a mutually exclusive expression system, and are encoded by the multigene var family. The mechanism whereby inactive var genes are silenced is poorly understood. To investigate transcriptional features of this mechanism, we conducted a microarray analysis of parasites that were selected to express different var genes by adhesion to chondroitin sulfate A (CSA) or CD36.
Results
In addition to oligonucleotides for all predicted protein-coding genes, oligonucleotide probes specific to each known var gene of the FCR3 background were designed and added to the microarray, as well as tiled sense and antisense probes for a subset of var genes. In parasites selected for adhesion to CSA, one full-length var gene (var2csa) was strongly upregulated, as were sense RNA molecules emanating from the 3' end of a limited subset of other var genes. No global relationship between sense and antisense production of var genes was observed, but notably, some var genes had coincident high levels of both antisense and sense transcript.
Conclusion
Mutually exclusive expression of PfEMP1 proteins results from transcriptional silencing of non-expressed var genes. The distribution of steady-state sense and antisense RNA at var loci are not consistent with a silencing mechanism based on antisense silencing of inactive var genes. Silencing of var loci is also associated with altered regulation of genes distal to var loci.
doi:10.1186/gb-2005-6-11-r93
PMCID: PMC1297649  PMID: 16277748

Results 1-18 (18)