Two ancient membrane pores mediate mitochondrial-nucleus membrane contact sites

Coordination between nucleus and mitochondria is essential for cell survival, and thus numerous communication routes have been established between these two organelles over eukaryotic cell evolution. One route for organelle communication is via membrane contact sites, functional appositions formed by molecular tethers. We describe a novel nuclear-mitochondrial membrane contact site in the protozoan Toxoplasma gondii. We have identified specific contacts occurring at the nuclear pore and demonstrated an interaction between components of the nuclear pore and the mitochondrial protein translocon, highlighting them as molecular tethers. Genetic disruption of the nuclear pore or the TOM translocon components, TgNup503 or TgTom40, respectively, result in contact site reduction, supporting their potential involvement in this tether. TgNup503 depletion further leads to specific mitochondrial morphology and functional defects, supporting a role for nuclear-mitochondrial contacts in mediating their communication. The discovery of a contact formed through interaction between two ancient mitochondrial and nuclear complexes sets the ground for better understanding of mitochondrial-nuclear crosstalk in eukaryotes.

Hydroxamate-based compounds are potent inhibitors of Toxoplasma gondii HDAC biological activity

Toxoplasmosis is a critical health issue for immune-deficient individuals and the offspring of newly infected mothers. It is caused by a unicellular intracellular parasite called Toxoplasma gondii that is found worldwide. Although efficient drugs are commonly used to treat toxoplasmosis, serious adverse events are common. Therefore, new compounds with potent anti-T. gondii activity are needed to provide better suited treatments. We have tested compounds designed to target specifically histone deacetylase enzymes. Among the 55 compounds tested, we identified three compounds showing a concentration of drug required for 50% inhibition (IC50) in the low 100 nM range with a selectivity index of more than 100. These compounds are not only active at inhibiting the growth of the parasite in vitro but also at preventing some of the consequences of the acute disease in vivo. Two of these hydroxamate based compound also induce a hyper-acetylation of the parasite histones while the parasitic acetylated tubulin level remains unchanged. These findings suggest that the enzymes regulating histone acetylation are potent therapeutic targets for the treatment of acute toxoplasmosis.

Deciphering the Role of Protein Phosphatases in Apicomplexa: The Future of Innovative Therapeutics?

Parasites belonging to the Apicomplexa phylum still represent a major public health and world-wide socioeconomic burden that is greatly amplified by the spread of resistances against known therapeutic drugs. Therefore, it is essential to provide the scientific and medical communities with innovative strategies specifically targeting these organisms. In this review, we present an overview of the diversity of the phosphatome as well as the variety of functions that phosphatases display throughout the Apicomplexan parasites’ life cycles. We also discuss how this diversity could be used for the design of innovative and specific new drugs/therapeutic strategies.

Primary brain cell infection by Toxoplasma gondii reveals the extent and dynamics of parasite differentiation and its impact on neuron biology

Toxoplasma gondii is a eukaryotic parasite that forms latent cysts in the brain of immunocompetent individuals. The latent parasite infection of the immune-privileged central nervous system is linked to most complications. With no drug currently available to eliminate the latent cysts in the brain of infected hosts, the consequences of neurons' long-term infection are unknown. It has long been known that T. gondii specifically differentiates into a latent form (bradyzoite) in neurons, but how the infected neuron responds to the infection remains to be elucidated. We have established a new in vitro model resulting in the production of mature bradyzoite cysts in brain cells. Using dual, host and parasite RNA-seq, we characterized the dynamics of differentiation of the parasite, revealing the involvement of key pathways in this process. Moreover, we identified how the infected brain cells responded to the parasite infection revealing the drastic changes that take place. We showed that neuronal-specific pathways are strongly affected, with synapse signalling being particularly affected, especially glutamatergic synapse signalling. The establishment of this new in vitro model allows investigating both the dynamics of parasite differentiation and the specific response of neurons to long-term infection by this parasite.

A toolbox for conditional control of gene expression in apicomplexan parasites

Apicomplexan parasites encompass diverse pathogens for humans and animals, including the causative agents of malaria and toxoplasmosis, Plasmodium spp. and Toxoplasma gondii. Genetic manipulation of these parasites has become central to explore parasite biology, unravel gene function and identify new targets for therapeutic strategies. Tremendous progress has been achieved over the past years with the advent of next generation sequencing and powerful genome editing methods. In particular, various methods for conditional gene expression have been developed in both Plasmodium and Toxoplasma to knockout or knockdown essential genes, or for inducible expression of master developmental regulators or mutant versions of proteins. Conditional gene expression can be achieved at three distinct levels. At the DNA level, inducible site‐specific recombinases allow conditional genome editing. At the RNA level, regulation can be achieved during transcription, using stage‐specific or regulatable promoters, or post‐transcriptionally through alteration of mRNA stability or translation. At the protein level, several systems have been developed for inducible degradation or displacement of a protein of interest. In this review, we provide an overview of current systems for conditional control of gene expression in Plasmodium and Toxoplasma parasites, highlighting the advantages and limitations of each approach.

A coiled-coil protein is required for coordination of karyokinesis and cytokinesis in Toxoplasma gondii

Toxoplasma gondii is a unicellular eukaryotic pathogen that belongs to the Apicomplexa phylum, which encompasses some of the deadliest pathogens of medical and veterinary importance. The centrosome is key to the organisation and coordination of the cell cycle and division of apicomplexan parasites. The T. gondii centrosome possesses a particular bipartite structure (outer and inner cores). One of the main roles of the centrosome is to ensure proper coordination of karyokinesis. However, how these 2 events are coordinated is still unknown in T. gondii, for which the centrosome components are poorly described. To gain more insights into the biology and the composition of the T. gondii centrosome, we characterised a protein that resides at the interface of the outer and inner core centrosomes. TgCep530 is a large coiled-coil protein with an essential role in the survival of the parasite. Depletion of this protein leads to the accumulation of parasites lacking nuclei and disruption of the normal cell cycle. Lack of TgCep530 results in a discoordination between the nuclear cycle and the budding cycle that yields fully formed parasites without nuclei. TgCep530 has a crucial role in the coordination of karyokinesis and cytokinesis.

mRNA export in the apicomplexan parasite Toxoplasma gondii: emerging divergent components of a crucial pathway

Control of gene expression is crucial for parasite survival and is the result of a series of processes that are regulated to permit fine-tuning of gene expression in response to biological changes during the life-cycle of apicomplexan parasites. Control of mRNA nuclear export is a key process in eukaryotic cells but is poorly understood in apicomplexan parasites. Here, we review recent knowledge regarding this process with an emphasis on T. gondii. We describe the presence of divergent orthologs and discuss structural and functional differences in export factors between apicomplexans and other eukaryotic lineages. Undoubtedly, the use of the CRISPR/Cas9 system in high throughput screenings associated with the discovery of mRNA nuclear export complexes by proteomic analysis will contribute to identify these divergent factors. Ligand-based or structure-based strategies may be applied to investigate the potential use of these proteins as targets for new antiprotozoal agents.

A RGG motif protein is involved in Toxoplasma gondii stress-mediated response

The molecular mechanisms controlling gene expression are still poorly understood in apicomplexan parasites. Here, we report the characterization of a homolog of the single strand binding proteins (named TgSsossB) in Toxoplasma gondii. We previously showed that TgSsossB interacts with the TgAlba proteins that are involved in translation regulation. We examined the role of TgSsossB in stress-mediated response, and particularly the role of its arginine-glycine-glycine (RGG) repeats domain. TgSsossB recombinant protein is able to bind to single strand DNA and RNA in a sequence-independent manner, but not to double stranded DNA. We showed that the RGG motif is not involved in this ability to bind to nucleic acid. We produced a mutant tagged strain lacking the RGG motif of TgSsossB using the knock-in strategy. We observed that this strain exhibited a fitness defect compared with the parental parasites. Moreover, the mutant strain produced fewer plaques in stress conditions, a defect that is due to a slow growth phenotype when extracellular parasites are exposed to stress. At the molecular level, we showed that the TgSsossB protein lacking a RGG motif lost its ability to interact with TgAlba2 and an isoform of TgAlba1, indicating that the TgAlba complex is likely non-functional in those parasites. Thus, our findings define the RGG domain of TgSsossB as a protein-protein interaction platform and underline the role of the TgAlba-TgSsossB complex in stress-mediated response.

Toxoplasma transcription factor TgAP2XI-5 regulates the expression of genes involved in parasite virulence and host invasion

Gene regulation in apicomplexan parasites, a phylum containing important protozoan parasites such as Plasmodium and Toxoplasma, is poorly understood. The life cycle of Toxoplasma gondii is complex, with multiple proliferation and differentiation steps, of which tachyzoite proliferation is the most relevant to pathogenesis in humans and animals. Tachyzoites express invasion and virulence factors that are crucial for their survival and manipulation of host cell functions. The expression of those factors is tightly controlled during the tachyzoite cell cycle to permit their correct packaging in newly formed apical secretory organelles named micronemes and rhoptries in the daughter cells. However, little is known about the factors that control the expression of genes encoding the virulence factors present in these parasite-specific secretory organelles. We report that the plant-like nuclear factor TgAP2XI-5 targets more than 300 gene promoters and actively controls the transcription of these genes. Most of these target genes, including those that are essential for parasite virulence, showed a peak of expression in the S and M phases of the cell cycle. Furthermore, we identified the cis-regulatory element recognized by TgAP2XI-5 and demonstrated its ability to actively drive gene transcription. Our results demonstrated that TgAP2XI-5 is a novel DNA sequence-specific transcription factor associated with promoter activation. TgAP2XI-5 may regulate gene transcription of crucial virulence factors in T. gondii.

Toxoplasma gondii Alba proteins are involved in translational control of gene expression

Molecular mechanisms controlling gene expression in apicomplexan parasites remain poorly understood. Here, we report the characterization of two Toxoplasma gondii homologs of the ancient archeal Alba proteins named TgAlba1 and TgAlba2. The targeted disruption of TgAlba1 and TgAlba2 genes in both virulent type I and avirulent type II strains of T. gondii reveals that TgAlba proteins may have an important role in regulating stress response. We found that although the steady-state level of the Tgalba2 transcript is increased in the ΔTgalba1 null mutant parasites, the cognate TgAlba2 protein is undetectable, suggesting that TgAlba1 is required for translation of TgAlba2. Using a tandem affinity purification tag strategy combined with proteomic analyses, we provide evidence that many factors known to be involved in the translation machinery are co-purified with TgAlba1 and TgAlba2. We further performed RNA pull-down and microarray analyses to show that TgAlba1 and TgAlba2 bind to more than 30 RNAs including their own transcripts. Moreover, we demonstrate that the tight translational regulation of the TgAlba2 endogenous transcript relies on the presence of both its 3' untranslated region and that of the TgAlba1 protein. Thus, our findings on TgAlba1 and TgAlba2 are consistent with a role in gene-specific translation.

The Toxoplasma nuclear factor TgAP2XI-4 controls bradyzoite gene expression and cyst formation

Toxoplasma gondii undergoes many phenotypic changes during its life cycle. The recent identification of AP2 transcription factors in T. gondii has provided a platform for studying the mechanisms controlling gene expression. In the present study, we report that a recombinant protein encompassing the TgAP2XI-4 AP2 domain was able to specifically bind to a DNA motif using gel retardation assays. TgAP2XI-4 protein is localized in the parasite nucleus throughout the tachyzoite life cycle in vitro, with peak expression occurring after cytokinesis. We found that the TgAP2XI-4 transcript level was higher in bradyzoite cysts isolated from brains of chronically infected mice than in the rapidly replicating tachyzoites. A knockout of the TgAP2XI-4 gene in both T. gondii virulent type I and avirulent type II strains reveals its role in modulating expression and promoter activity of genes involved in stage conversion of the rapidly replicating tachyzoites to the dormant cyst forming bradyzoites. Furthermore, mice infected with the type II KO mutants show a drastically reduced brain cyst burden. Thus, our results validate TgAP2XI-4 as a novel nuclear factor that regulates bradyzoite gene expression during parasite differentiation and cyst formation.

Toxoplasma gondii chromodomain protein 1 binds to heterochromatin and colocalises with centromeres and telomeres at the nuclear periphery

Background

Apicomplexan parasites are responsible for some of the most deadly parasitic diseases afflicting humans, including malaria and toxoplasmosis. These obligate intracellular parasites exhibit a complex life cycle and a coordinated cell cycle-dependant expression program. Their cell division is a coordinated multistep process. How this complex mechanism is organised remains poorly understood.

Methods and Findings

In this study, we provide evidence for a link between heterochromatin, cell division and the compartmentalisation of the nucleus in Toxoplasma gondii. We characterised a T. gondii chromodomain containing protein (named TgChromo1) that specifically binds to heterochromatin. Using ChIP-on-chip on a genome-wide scale, we report TgChromo1 enrichment at the peri-centromeric chromatin. In addition, we demonstrate that TgChromo1 is cell-cycle regulated and co-localised with markers of the centrocone. Through the loci-specific FISH technique for T. gondii, we confirmed that TgChromo1 occupies the same nuclear localisation as the peri-centromeric sequences.

Conclusion

We propose that TgChromo1 may play a role in the sequestration of chromosomes at the nuclear periphery and in the process of T. gondii cell division.

How epigenomics contributes to the understanding of gene regulation in Toxoplasma gondii

How apicomplexan parasites regulate their gene expression is poorly understood. The complex life cycle of these parasites implies tight control of gene expression to orchestrate the appropriate expression pattern at the right moment. Recently, several studies have demonstrated the role of epigenetic mechanisms for control of coordinated expression of genes. In this review, we discuss the contribution of epigenomics to the understanding of gene regulation in Toxoplasma gondii. Studying the distribution of modified histones on the genome links chromatin modifications to gene expression or gene repression. In particular, coincident trimethylated lysine 4 on histone H3 (H3K4me3), acetylated lysine 9 on histone H3 (H3K9ac), and acetylated histone H4 (H4ac) mark promoters of actively transcribed genes. However, the presence of these modified histones at some non-expressed genes and other histone modifications at only a subset of active promoters implies the presence of other layers of regulation of chromatin structure in T. gondii. Epigenomics analysis provides a powerful tool to characterize the activation state of genomic loci of T. gondii and possibly of other Apicomplexa including Plasmodium or Cryptosporidium. Further, integration of epigenetic data with expression data and other genome-wide datasets facilitates refinement of genome annotation based upon experimental data.

Attenuated Plasmodium yoelii lacking purine nucleoside phosphorylase confer protective immunity

Malaria continues to devastate sub-Saharan Africa owing to the emergence of drug resistance to established antimalarials and to the lack of an efficacious vaccine. Plasmodium species have a unique streamlined purine pathway in which the dual specificity enzyme purine nucleoside phosphorylase (PNP) functions in both purine recycling and purine salvage. To evaluate the importance of PNP in an in vivo model of malaria, we disrupted PyPNP, the gene encoding PNP in the lethal Plasmodium yoelii YM strain. P. yoelii parasites lacking PNP were attenuated and cleared in mice. Although able to form gametocytes, PNP-deficient parasites did not form oocysts in mosquito midguts and were not transmitted from mosquitoes to mice. Mice given PNP-deficient parasites were immune to subsequent challenge to a lethal inoculum of P. yoelii YM and to challenge from P. yoelii 17XNL, another strain. These in vivo studies with PNP-deficient parasites support purine salvage as a target for antimalarials. They also suggest a strategy for the development of attenuated nontransmissible metabolic mutants as blood-stage malaria vaccine strains.

New eukaryotic systematics: a phylogenetic perspective of developmental gene expression in the Apicomplexa

The phylum Apicomplexa consists of obligate intracellular protistan parasites, some of which are responsible for global disease causing serious morbidity and mortality in humans and animals. Understanding the mechanisms of gene expression that drive the cellular changes required to complete their life cycles will be critical in combating infection and disease. Plasmodium spp. and Toxoplasma gondii have served as good models for growth and development in the Apicomplexa. Elucidating developmental gene expression relies on comparisons with known mechanisms and their DNA, RNA and protein components. Transcriptional profiling across asexual development suggests a model where a cascade of gene expression results in a "just-in-time" production process that makes products only when needed. Some mechanisms that control transcription such as chromatin/histone modification are highly conserved in the phylum compared with the traditional model organisms, yeast, worms, flies and mammals. Studies exploiting this phenomenon show great potential for both investigating the effects of chromatin structure on developmental gene expression, and helping to identify genes that are expressed in a stage-specific manner. Transcription factors and their cognate cis-acting binding sites have been difficult to identify. This may be because the DNA binding motifs that have evolved to act as transcription factors in the Apicomplexa, e.g. the AP2 family, may be more like plants than the traditional model organisms. A new eukaryotic phylogenetic model comprised of six super-groups divides the traditional model organisms, plants and the Apicomplexa into separate super-groups. This phylogenetic model helps explain why basic functions such as transcriptional regulation appear be a composite of mechanisms in the Apicomplexa compared with what is known from other eukaryotes.

High mobility group protein HMGB2 is a critical regulator of plasmodium oocyst development

The sexual cycle of Plasmodium is required for transmission of malaria from mosquitoes to mammals, but how parasites induce the expression of genes required for the sexual stages is not known. We disrupted the Plasmodium yoelii gene encoding high mobility group nuclear factor hmgb2, which encodes a DNA-binding protein potentially implicated in transcriptional regulation of malaria gene expression. We investigated its function in vivo in the vertebrate and invertebrate hosts. Deltapyhmgb2 parasites develop into gametocytes but have drastic impairment of oocyst formation. A global transcriptome analysis of the Deltapyhmgb2 parasites identified approximately 30 genes whose expression is down-regulated in the Deltapyhmgb2 parasites. These genes are conserved in all malaria species, and more than 90% of these genes show a peak of mRNA expression at the gametocyte stage. Surprisingly, the transcripts coding for the Plasmodium berghei orthologues of those genes are stored and translated in the ookinete stage. Therefore, sexual stage protein expression appears to be both transcriptionally and translationally regulated with Plasmodium HMGB2 acting as an important regulator of malaria sexual stage gene expression.

An analytical pipeline for genomic representations used for cytosine methylation studies

MOTIVATION

Representations of the genome can be generated by the selection of a subpopulation of restriction fragments using ligation-mediated PCR. Such representations form the basis for a number of high-throughput assays, including the HELP assay to study cytosine methylation. We find that HELP data analysis is complicated not only by PCR amplification heterogeneity but also by a complex and variable distribution of cytosine methylation. To address this, we created an analytical pipeline and novel normalization approach that improves concordance between microarray-derived data and single locus validation results, demonstrating the value of the analytical approach. A major influence on the PCR amplification is the size of the restriction fragment, requiring a quantile normalization approach that reduces the influence of fragment length on signal intensity. Here we describe all of the components of the pipeline, which can also be applied to data derived from other assays based on genomic representations.

Epigenomic modifications predict active promoters and gene structure in Toxoplasma gondii

Mechanisms of gene regulation are poorly understood in Apicomplexa, a phylum that encompasses deadly human pathogens like Plasmodium and Toxoplasma. Initial studies suggest that epigenetic phenomena, including histone modifications and chromatin remodeling, have a profound effect upon gene expression and expression of virulence traits. Using the model organism Toxoplasma gondii, we characterized the epigenetic organization and transcription patterns of a contiguous 1% of the T. gondii genome using custom oligonucleotide microarrays. We show that methylation and acetylation of histones H3 and H4 are landmarks of active promoters in T. gondii that allow us to deduce the position and directionality of gene promoters with >95% accuracy. These histone methylation and acetylation “activation” marks are strongly associated with gene expression. We also demonstrate that the pattern of histone H3 arginine methylation distinguishes certain promoters, illustrating the complexity of the histone modification machinery in Toxoplasma. By integrating epigenetic data, gene prediction analysis, and gene expression data from the tachyzoite stage, we illustrate feasibility of creating an epigenomic map of T. gondii tachyzoite gene expression. Further, we illustrate the utility of the epigenomic map to empirically and biologically annotate the genome and show that this approach enables identification of previously unknown genes. Thus, our epigenomics approach provides novel insights into regulation of gene expression in the Apicomplexa. In addition, with its compact genome, genetic tractability, and discrete life cycle stages, T. gondii provides an important new model to study the evolutionarily conserved components of the histone code.

Apicomplexan parasites, including Toxoplasma gondii, are responsible for a variety of deadly infections, but little is understood about how these important pathogens regulate gene expression. Initial studies suggest that alterations in chromatin structure regulate expression of virulence traits. To understand the relationship of chromatin remodeling and transcriptional regulation in T. gondii, we characterized the histone modifications and gene expression of a contiguous 1% of the T. gondii genome using custom DNA oligonucleotide microarrays. We found that active promoters have a characteristic pattern of histone modifications that correlates strongly with active gene expression in tachyzoites. These data, integrated with prior gene predictions, enable more accurate annotation of the genome and discovery of new genes. Further, these studies illustrate the power of an integrated epigenomic approach to illuminate the role of the “histone code” in regulation of gene expression in the Apicomplexa.

High-mobility-group box nuclear factors of Plasmodium falciparum

In eukaryotes, the high-mobility-group (HMG) nuclear factors are highly conserved throughout evolution and are divided into three families, including HGMB, characterized by an HMG box domain. Some HMGB factors are DNA structure specific and preferentially interact with distorted DNA sequences, trigger DNA bending, and hence facilitate the binding of nucleoprotein complexes that in turn activate or repress transcription. In Plasmodium falciparum, two HMGB factors were predicted: PfHMGB1 and PfHMGB2. They are small proteins, under 100 amino acids long, encompassing a characteristic HMG box domain closely related to box B of metazoan factors, which comprises two HMG box domains, A and B, in tandem. Computational analyses supported the conclusion that the Plasmodium proteins were genuine architectural HMGB factors, and in vitro analyses performed with both recombinant proteins established that they were able to interact with distorted DNA structures and bend linear DNA with different affinities. These proteins were detected in both asexual- and gametocyte-stage cells in Western blotting experiments and mainly in the parasite nuclei. PfHMGB1 is preferentially expressed in asexual erythrocytic stages and PfHMGB2 in gametocytes, in good correlation with transcript levels of expression. Finally, immunofluorescence studies revealed differential subcellular localizations: both factors were observed in the nucleus of asexual- and sexual-stage cells, and PfHMGB2 was also detected in the cytoplasm of gametocytes. In conclusion, in light of differences in their levels of expression, subcellular localizations, and capacities for binding and bending DNA, these factors are likely to play nonredundant roles in transcriptional regulation of Plasmodium development in erythrocytes.

PfMyb1, a Plasmodium falciparum transcription factor, is required for intra-erythrocytic growth and controls key genes for cell cycle regulation

During the complex life cycle of Plasmodium falciparum, divided between mosquito and human hosts, the regulation of morphologic changes implies a fine control of transcriptional regulation. Transcriptional control, however, and in particular its molecular actors, transcription factors and regulatory motifs, are as yet poorly described in Plasmodium. In order to decipher the molecular mechanisms implicated in transcriptional regulation, a transcription factor belonging to the tryptophan cluster family was studied. In a previous work, the PfMyb1 protein, contained in nuclear extracts, was shown to have DNA binding activity and to interact specifically with myb regulatory elements. We used long pfmyb1 double-stranded RNA (dsRNA) to interfere with the cognate messenger expression. Parasite cultures treated with pfmyb1 dsRNA exhibited a 40% growth inhibition when compared with either untreated cultures or cultures treated with unrelated dsRNA, and parasite mortality occurred during trophozoite to schizont transition. In addition, the pfmyb1 transcript and protein decreased by as much as 80% in treated trophozoite cultures at the time of their maximum expression. The global effect of this partial loss of transcript and protein was investigated using a thematic DNA microarray encompassing genes involved in signal transduction, cell cycle and transcriptional regulation. SAM software enabled us to identify several genes that were differentially expressed and probably directly or indirectly under the control of PfMyb1. Using chromatin immuno-precipitation, we demonstrated that PfMyb1 binds, within the parasite nuclei, to several promoters and therefore participates directly in the transcriptional regulation of the corresponding genes. This study provides the first evidence of a regulation network involving a Plasmodium transcription factor.

Transcriptome of 3D7 and its gametocyte-less derivative F12 Plasmodium falciparum clones during erythrocytic development using a gene-specific microarray assigned to gene regulation, cell cycle and transcription factors

During the complex life cycle of Plasmodium falciparum, through mosquito and human, the erythrocytic cycle is responsible for malarial disease and transmission. The regulation of events that occur during parasite development, such as proliferation and differentiation, implies a fine control of transcriptional activities that in turn governs the expression profiles of sets of genes. Pathways that underline gametocyte commitment are yet poorly understood even though kinases and transcription factors have been assumed to play a crucial role in this event. In order to understand the molecular mechanisms controlling the variation of gene expression profiles that might participate in early gametocytogenesis, the transcriptome of two clones, 3D7 and its gametocyte-less derivative F12, was compared at five time points of the erythrocytic asexual development. We have used a thematic DNA microarray containing 150 PCR fragments, representative of P. falciparum genes involved in signal transduction, cell cycle and transcriptional regulation. We identified several genes eliciting different expression profiles among which some implicated in gene regulation or encoding putative transcription factors. The differential expression of transcription factor and kinase transcripts observed in the two clones may enlighten genes that might have a role in impairment of the early gametocytogenesis of the F12 clone.

[Progress towards the use of DNA microarray technology for the study of wild Plasmodium strains]

Plasmodium falciparum is still a major cause of mortality in the world. Due to growing drug resistance in most endemic countries, the use of tools allowing large-scale analysis of P. falciparum biology is increasingly urgent. In addition to gene sequence data, post-genomic methods including microarray-based transcript profiling allow complete Plasmodium gene expression. However, application of this technology has been limited to study of samples presenting large quantities of total RNA (8 microg to 50 microg). Indeed at least two replicas (one technical and one biological) are necessary to ensure the statistical strength of results. This constraint excludes the use of biological materials hardly available and of wild strain samples. Many methods have been developed to facilitate the use of microarray technology with smaller quantities of total RNA. Currently the use of amplification techniques, various fluorochrome markers, and labelled cDNA and/or RNA probes avoiding all amplification steps, to enhance detection sensitivity has enabled reliable assays to be performed with less material. However these enhancement techniques appear to have a biasing effect on results and the use of powerful new markers is still limited for technical and practical reasons. At the present time radioactive labeling is the most reliable technique for assays using small quantities of total RNA. This approach is not only compatible with competitive hybridization but also enables all microarray screening criteria. Findings from our laboratory support the effectiveness of radioactive labeling for microarray-based determinations on P. falciparum.

Absence of weight loss during Cryptosporidium infection in susceptible mice deficient in Fas-mediated apoptosis

Apoptosis plays a major role in the development of pathogenesis due to a number of microbial infections. Epithelial cells have been previously shown to die through apoptosis during in vitro infection by the Apicomplexan parasite Cryptosporidium parvum. We now test the possibility that Fas (APO-1/CD95)-dependent apoptosis of uninfected cells, due to enhanced expression of the Fas ligand (FasL) on infected cells, may contribute to the pathology of cryptosporidiosis. Expression of the FasL increased by a large amount on the surface of intestinal epithelial cells infected with C. parvum, and the increase was limited exclusively to infected cells. In addition, a significant increase in FasL expression was observed in epithelial cells from the small intestine of mice infected with C. parvum. Finally, whereas wild-type mice depleted of CD4(+) lymphocytes lost weight during C. parvum infection, CD4(+) cell-depleted lpr mice (deficient in Fas function) infected with C. parvum gained weight at the same rate as undepleted wild-type or lpr mice. These results suggest that bystander Fas-dependent apoptosis of uninfected epithelial cells may exacerbate the weight loss associated with cryptosporidiosis.