Search

We analyze how environmental taxes should be optimally levied when the regulators and firms face costs uncertainties in a Stackelberg-Cournot game. We allow linear-quadratic payoffs functions coupled with an affine information structure encompassing common and private information with noisy signals. In the first period, the regulator chooses the intensity of emissions taxes in order to reduce externalities. In the second period, facing industry-related and firm-specific shocks, firms compete in the marketplace as Cournot rivals and choose outputs. We show that, given costs uncertainties with non-uniform quality of signals across firms, the regulator sets differentiated tax policy. We also examined the social value of information under ex-ante calibrated emissions taxes. We argue that the magnitude of the associated social benefits and costs of more precise private signals hinge largely and fundamentally on the value of the ratio of the slopes of the marginal damage and the marginal consumer surplus. The lack of accurate data clouds the regulatory process by preventing the necessary fine-tuning of the tax rules towards specific environmental circumstances. Finally, we investigate information sharing between polluters and its impacts on welfare. We stress that, when there are threats of severe environmental damages under deep uncertainties, collusion is welfare reducing and may jeopardize the regulatory process. Numerical simulations illustrate the results that the model delivers.

Pathogenic mycobacteria gain entry to their hosts by inhalation or ingestion where they adhere to different cell types and are subsequently internalized by professional phagocytic cells, such as macrophages or dendritic cells. Multiple pathogen-associated molecular patterns present on the mycobacterial surface are recognized by and interact with a diverse panel of phagocytic pattern recognition receptors, representing the first step of the infection process. This review summarizes the current knowledge on the numerous host cell receptors and their associated mycobacterial ligands or adhesins. It further discusses the downstream molecular and cellular events resulting from the engagement of the various receptor-mediated pathways, leading to either intracellular survival of mycobacteria or to activation of host immune defenses. The content presented herein on adhesins and host receptors may serve as a resource for those developing novel therapeutic approaches, e.g. in the design of antiadhesin molecules to prevent bacterial attachment and infection. The collection of mycobacterial surface molecules highlighted in this review may also provide potential new therapeutic targets, diagnostic markers, or vaccine candidates to combat these notoriously challenging and persistent pathogens.

Inborn errors of human IFN-γ-dependent macrophagic immunity underlie mycobacterial diseases, whereas inborn errors of IFN-α/β-dependent intrinsic immunity underlie viral diseases. Both types of IFNs induce the transcription factor IRF1. We describe unrelated children with inherited complete IRF1 deficiency and early-onset, multiple, life-threatening diseases caused by weakly virulent mycobacteria and related intramacrophagic pathogens. These children have no history of severe viral disease, despite exposure to many viruses, including SARS-CoV-2, which is life-threatening in individuals with impaired IFN-α/β immunity. In leukocytes or fibroblasts stimulated in vitro, IRF1-dependent responses to IFN-γ are, both quantitatively and qualitatively, much stronger than those to IFN-α/β. Moreover, IRF1-deficient mononuclear phagocytes do not control mycobacteria and related pathogens normally when stimulated with IFN-γ. By contrast, IFN-α/β-dependent intrinsic immunity to nine viruses, including SARS-CoV-2, is almost normal in IRF1-deficient fibroblasts. Human IRF1 is essential for IFN-γ-dependent macrophagic immunity to mycobacteria, but largely redundant for IFN-α/β-dependent antiviral immunity.

Transmission of Plasmodium falciparum and other malaria parasites requires their differentiation from asexual blood stages into gametocytes, the non-replicative sexual stage necessary to infect the mosquito vector. This transition involves changes in gene expression and chromatin reorganization that result in the activation and silencing of stage-specific genes. However, the genomes of malaria parasites have been noted for their limited number of transcriptional and chromatin regulators, and the molecular mediators of these changes remain largely unknown. We recently identified homeodomain protein 1 (HDP1) as a DNA-binding protein, first expressed in gametocytes, that enhances the expression of key genes critical for early sexual differentiation. The discovery of HDP1 marks a new class of transcriptional regulator in malaria parasites outside of the better-characterized ApiAP2 family. Here, using molecular biology, biochemistry and microscopy techniques, we show that HDP1 is essential for gametocyte maturation, facilitating the necessary upregulation of inner membrane complex components during early gametocytogenesis that gives P. falciparum gametocytes their characteristic shape.

ESX type VII secretion systems are complex secretion machineries spanning across the mycobacterial membrane and play an important role in pathogenicity, nutrient uptake and conjugation. We previously reported the role of ESX-4 in modulating Mycobacterium abscessus intracellular survival. The loss of EccB4 was associated with limited secretion of two effector proteins belonging to the WXG-100 family, EsxU and EsxT, and encoded by the esx-4 locus. This prompted us to investigate the function of M. abscessus EsxU and EsxT in vitro and in vivo. Herein, we show that EsxU and EsxT are substrates of ESX-4 and form a stable 1:1 heterodimer that permeabilizes artificial membranes. While expression of esxU and esxT was up-regulated in M. abscessus-infected macrophages, their absence in an esxUT deletion mutant prevented phagosomal membrane disruption while maintaining M. abscessus in an unacidified phagosome. Unexpectedly, the esxUT deletion was associated with a hyper-virulent phenotype, characterised by increased bacterial loads and mortality in mouse and zebrafish infection models. Collectively, these results demonstrate that the presence of EsxU and EsxT dampens survival and persistence of M. abscessus during infection.

International audience; Mycobacterium abscessus is an emerging and difficult-to-manage mycobacterial species that exhibits smooth (S) or rough (R) morphotypes. Disruption of glycopeptidolipid (GPL) production results in transition from S to R and severe lung disease. A structure-activity relationship study was undertaken to decipher the role of GPL glycosylation in morphotype transition and pathogenesis. Deletion of gtf3 uncovered the prominent role of the extra rhamnose in enhancing mannose receptor-mediated internalization of M. abscessus by macrophages. In contrast, the absence of the 6-deoxy-talose and the first rhamnose in mutants lacking gtf1 and gtf2, respectively, affected M abscessus phagocytosis but also resulted in the S-to-R transition. Strikingly, gtf1 and gtf2 mutants displayed a strong propensity to form cords and abscesses in zebrafish, leading to robust and lethal infection. Together, these results underscore the importance and differential contribution of GPL monosaccharides in promoting virulence and infection outcomes.

This paper presents an analysis of environmental policy in imperfectly competitive market with publicly disclosed and privately-held information about costs. We examine the potential asymmetry-reducing role of disclosure and its impact on setting environmental taxes. From a policy perspective, our findings show that disclosure with verifiable reports, is a valuable public good, provides greater transparency in the market, and is generally efficiency enhancing. Results suggest that access to publicly disclosed information enables the fine-tuning of the tax rules towards specific environmental circumstances and improves the ability of the regulator to levy firm-specific environmental taxes. Further, while we do not attempt to analyze the exchange of information process between players, our findings show that, despite its advantages, exogenously disclosed information can be double-edged sword since it may also produce anticompetitive effects by facilitating collusive behavior. Information sharing between firms may occur and thus lead to a superior outcome in terms of industry output and emissions, which undermines environmental policy performance.

Transmission of Plasmodium falciparum and other malaria parasites requires their differentiation from asexual blood stages into gametocytes, the non-replicative sexual stage necessary to infect the mosquito vector. This transition involves changes in gene expression and chromatin reorganization that result in the activation and silencing of stage-specific genes. However, the genomes of malaria parasites have been noted for their limited number of transcriptional and chromatin regulators, and the molecular mediators of these changes remain largely unknown. We recently identified homeodomain protein 1 (HDP1) as a DNA-binding protein, first expressed in gametocytes, that enhances the expression of key genes critical for early sexual differentiation. The discovery of HDP1 marks a new class of transcriptional regulator in malaria parasites outside of the better-characterized ApiAP2 family. Here, using molecular biology, biochemistry and microscopy techniques, we show that HDP1 is essential for gametocyte maturation, facilitating the necessary upregulation of inner membrane complex components during early gametocytogenesis that gives P. falciparum gametocytes their characteristic shape.

Transmission of Plasmodium falciparum and other malaria parasites requires their differentiation from asexual blood stages into gametocytes, the non-replicative sexual stage necessary for transmission to the mosquito vector. This transition involves changes in gene expression and chromatin reorganization that result in the activation and silencing of stage-specific genes. However, the genomes of malaria parasites have been noted for their dearth of transcriptional and chromatin regulators and the molecular mediators of these changes remain largely unknown. We recently identified HomeoDomain Protein 1 (HDP1) as a DNA-binding protein that enhances the expression of key genes that are critical for early sexual differentiation. The discovery of a homeodomain-like DNA-binding protein marks a new class of transcriptional regulator in malaria parasites outside of the better-characterized ApiAP2 family. In this study, we show that HDP1 facilitates the necessary upregulation of inner membrane complex components during early gametocytogenesis that gives P. falciparum gametocytes they characteristic shape and is required for gametocyte maturation and parasite transmission.

International audience; Mycobacterium abscessus, an emerging pathogen responsible for severe lung infections in cystic fibrosis patients, displays either smooth (S) or rough (R) morphotypes. The S-to-R transition is associated with reduced levels of glycopeptidolipid (GPL) production and is correlated with increased pathogenicity in animal and human hosts. While the structure of GPL is well established, its biosynthetic pathway is incomplete. In addition, the biological functions of the distinct structural parts of this complex lipid remain elusive. Herein, the fmt gene encoding a putative O-methyltransferase was deleted in the M. abscessus S variant. Subsequent biochemical and structural analyses demonstrated that methoxylation of the fatty acyl chain of GPL was abrogated in the Δfmt mutant, and this defect was rescued upon complementation with a functional fmt gene. In contrast, the introduction of fmt derivatives mutated at residues essential for methyltransferase activity failed to complement GPL defects, indicating that fmt encodes an O-methyltransferase. Unexpectedly, phenotypic analyses showed that Δfmt was more hydrophilic than its parental progenitor, as demonstrated by hexadecane-aqueous buffer partitioning and atomic force microscopy experiments with hydrophobic probes. Importantly, the invasion rate of THP-1 macrophages by Δfmt was reduced by 50% when compared to the wild-type strain. Together, these results indicate that Fmt O-methylates the lipid moiety of GPL and plays a substantial role in conditioning the surface hydrophobicity of M. abscessus as well as in the early steps of the interaction between the bacilli and macrophages.

International audience; Tetraspanins, a wide family composed of 33 transmembrane proteins, are associated with different types of proteins through which they arbitrate important cellular processes such as fusion, adhesion, invasion, tissue differentiation and immunological responses. Tetraspanins share a comparable structural design, which consists of four hydrophobic transmembrane domains with cytoplasmic and extracellular loops. They cooperate with different proteins, including other tetraspanins, receptors or signalling proteins to compose functional complexes at the cell surface, designated tetraspanin-enriched microdomains (TEM). Increasing evidences establish that tetraspanins are exploited by numerous intracellular pathogens as a doorway for entering and replicating within human cells. Although previous surveys focused mainly on viruses and parasites, it is now becoming clear that bacteria interact with tetraspanins, using TEM as a "gateway" to infection. In this review, we examine the biological functions of tetraspanins that are relevant to bacterial infective procedures and consider the available data that reveal how different bacteria benefit from host cell tetraspanins in infection and in the pathogenesis of diseases. We will also emphasise the stimulating potentials of targeting tetraspanins for preventing bacterial infectious diseases, using specific neutralising antibodies or anti-adhesion peptide-based therapies. Such innovative therapeutic opportunities may deliver alternatives for fighting difficult-to-manage and drug-resistant bacterial pathogens.

New drugs or therapeutic combinations are urgently needed against Mycobacterium abscessus . Previously, we demonstrated the potent activity of indole-2-carboxamides 6 and 12 against M. abscessus . We show here that these compounds act synergistically with imipenem and cefoxitin in vitro and increase the bactericidal activity of the β-lactams against M. abscessus . In addition, compound 12 also displays synergism with imipenem and cefoxitin within infected macrophages.

The prevalence of pulmonary infections due to nontuberculous mycobacteria such as

International audience; The prevalence of pulmonary infections due to non-tuberculous mycobacteria such as Mycobacterium abscessus, has been increasing and surpassing tuberculosis (TB) in some industrialized countries. Due to intrinsic resistance to most antibiotics that drastically limits conventional chemotherapeutic treatment options, new anti-M. abscessus therapeutics are urgently needed against this emerging pathogen. Extensive screening of a library of benzimidazole derivatives that were previously shown to be active against Mycobacterium tuberculosis led to the identification of a lead compound exhibiting very potent in vitro activity against a wide panel of M. abscessus clinical strains. Designated EJMCh-6, this compound, a 2-(2-cyclohexylethyl)-5,6-dimethyl-1H-benzo[d]imidazole), also exerted a very strong activity against intramacrophage-residing M. abscessus. Moreover, treatment of infected zebrafish embryos with EJMCh-6 correlated with a significantly increased embryo survival and a decrease in the bacterial burden as compared to untreated fish. Insights into the mechanism of action were inferred from the generation of spontaneous benzimidazole-resistant strains and the identification of a large set of missense mutations in MmpL3; the mycolic acid transporter in mycobacteria. Over-expression of the mutated mmpL3 alleles in a susceptible M. abscessus strain was associated with high resistance levels to EJMCh-6 and to other known MmpL3 inhibitors. Mapping the mutations conferring resistance on a MmpL3 three-dimensional homology model defined a potential EJMCh-6-binding cavity. These data emphasize a yet unexploited chemical structure class against M. abscessus with promising translational developments for the treatment of M. abscessus lung diseases.

Toxoplasma gondii is the causative agent of toxoplasmosis. The pathogenicity of this unicellular parasite is tightly linked to its ability to efficiently proliferate within its host. Tachyzoites, the fast dividing form of the parasite, divide by endodyogeny. This process involves a single round of DNA replication, closed nuclear mitosis, and assembly of two daughter cells within a mother. The successful completion of endodyogeny relies on the temporal and spatial coordination of a plethora of simultaneous events. It has been shown that the Toxoplasma centrosome serves as signaling hub which nucleates spindle microtubules during mitosis and organizes the scaffolding of daughter cells components during cytokinesis. In addition, the centrosome is essential for inheriting both the apicoplast (a chloroplast-like organelle) and the Golgi apparatus. A growing body of evidence supports the notion that the T. gondii centrosome diverges in protein composition, structure and organization from its counterparts in higher eukaryotes making it an attractive source of potentially druggable targets. Here, we summarize the current knowledge on T. gondii centrosomal proteins and extend the putative centrosomal protein repertoire by in silico identification of mammalian centrosomal protein orthologs. We propose a working model for the organization and architecture of the centrosome in Toxoplasma parasites. Experimental validation of our proposed model will uncover how each predicted protein translates into the biology of centrosome, cytokinesis, karyokinesis, and organelle inheritance in Toxoplasma parasites.

Due to intrinsic multidrug resistance, pulmonary infections with Mycobacterium abscessus are extremely difficult to treat. Previously, we demonstrated that bedaquiline is highly effective against Mycobacterium abscessus both in vitro and in vivo . Here, we report that verapamil improves the efficacy of bedaquiline activity against M. abscessus clinical isolates and low-level resistant strains, both in vitro and in macrophages.

This paper examines the impact of different risk attitudes on the financial decisions of two insiders trading in the stock market. We consider a static version of the Kyle (Econometrica 53:1315–1335, 1985) model with two insiders. Insider 1 is risk neutral while insider 2 is risk averse with negative exponential utility. First, we analytically prove the existence of a unique linear equilibrium. Second, we carry out a comparative static analysis with respect to the duopoly case of risk-neutral insiders (Tighe in Three essays on insider trading. Unpublished Ph.D dissertation, University of Illinois at Champaign-Urbana, 1989) and with respect to the duopoly case of risk-averse insiders (Holden and Subrahmanyam in Econ Lett 44:181–190, 1994) models. Our findings reveal that the market depth and the information revelation are higher in Tighe (1989) than in our model. However, compared to Holden and Subrahmanyam (1994), we find that the market depth depends crucially on the degree of risk aversion. Finally, we show that regardless of the degree of risk aversion, the stock price reveals more information in our model than the stock price in Holden and Subrahmanyam (1994).

The phosphoinositide phosphatidylinositol-3,5-bisphosphate (PI(3,5)P2) plays crucial roles in the maintenance of lysosome/vacuole morphology, membrane trafficking and regulation of endolysosome-localized membrane channel activity. In Toxoplasma gondii, we previously reported that PI(3,5)P2 is essential for parasite survival by controlling homeostasis of the apicoplast, a particular organelle of algal origin. Here, by using a phosphoinositide pull-down assay, we identified TgPH1 in Toxoplasma a protein conserved in many apicomplexan parasites. TgPH1 binds specifically to PI(3,5)P2, shows punctate intracellular localization, but plays no vital role for tachyzoite growth in vitro. TgPH1 is a protein predominantly formed by a pleckstrin homology (PH) domain. So far, PH domains have been described to bind preferentially to bis- or trisphosphate phosphoinositides containing two adjacent phosphates (i.e. PI(3,4)P2, PI(4,5)P2, PI(3,4,5)P3). Therefore, our study reveals an unusual feature of TgPH1 which binds preferentially to PI(3,5)P2.

Aurora kinases are eukaryotic serine/threonine protein kinases that regulate key events associated with chromatin condensation, centrosome and spindle function and cytokinesis. Elucidating the roles of Aurora kinases in apicomplexan parasites is crucial to understand the cell cycle control during Plasmodium schizogony or Toxoplasma endodyogeny. Here, we report on the localization of two previously uncharacterized Toxoplasma Aurora-related kinases (Ark2 and Ark3) in tachyzoites and of the uncharacterized Ark3 orthologue in Plasmodium falciparum erythrocytic stages. In Toxoplasma gondii, we show that TgArk2 and TgArk3 concentrate at specific sub-cellular structures linked to parasite division: the mitotic spindle and intranuclear mitotic structures (TgArk2), and the outer core of the centrosome and the budding daughter cells cytoskeleton (TgArk3). By tagging the endogenous PfArk3 gene with the green fluorescent protein in live parasites, we show that PfArk3 protein expression peaks late in schizogony and localizes at the periphery of budding schizonts. Disruption of the TgArk2 gene reveals no essential function for tachyzoite propagation in vitro, which is surprising giving that the P. falciparum and P. berghei orthologues are essential for erythrocyte schizogony. In contrast, knock-down of TgArk3 protein results in pronounced defects in parasite division and a major growth deficiency. TgArk3-depleted parasites display several defects, such as reduced parasite growth rate, delayed egress and parasite duplication, defect in rosette formation, reduced parasite size and invasion efficiency and lack of virulence in mice. Our study provides new insights into cell cycle control in Toxoplasma and malaria parasites and highlights Aurora kinase 3 as potential drug target.

Phosphoinositides are the phosphorylated derivatives of the structural membrane phospholipid phosphatidylinositol. Single or combined phosphorylation at the 3, 4 and 5 positions of the inositol ring gives rise to the seven different species of phosphoinositides. All are quantitatively minor components of cellular membranes but have been shown to have important functions in multiple cellular processes. Here we describe our current knowledge of phosphoinositide metabolism and functions in apicomplexan parasites, mainly focusing on Toxoplasma gondii and Plasmodium spp. Even though our understanding is still rudimentary, phosphoinositides have already shown their importance in parasite biology and revealed some very particular and parasite-specific functions. Not surprisingly, there is a strong potential for phosphoinositide synthesis to be exploited for future anti-parasitic drug development.

Toxoplasma gondii which is a member of the coccidian parasites owns a spatially polarized secretory system, which synthesizes de novo micronemes and rhoptries. These apical secretory organelles discharge their contents into host cells promoting invasion and survival. Herein, we identified a novel Coccidian Specific CORVET/HOPS Associated Protein (CSCHAP) belonging to the interaction network of both tethering complexes. CSCHAP is associated with the endomembrane system, rhoptries, micronemes and probably to the inner core of the conoid. Conditional depletion of CSCHAP leads to apical disconnection of rhoptries, aberrant apical organelles biogenesis and severely hinders T. gondii invasion. Overall, our study provides new insights into the mechanisms underpinning secretory organelles biogenesis in coccidian parasites.

The phylum Apicomplexa encompasses deadly pathogens such as malaria and Cryptosporidium. Apicomplexa cell division is mechanistically divergent from that of their mammalian host, potentially representing an attractive source of drug targets. Depending on the species, apicomplexan parasites can modulate the output of cell division, producing two to thousands of daughter cells at once. The inherent flexibility of their cell division mechanisms allows these parasites to adapt to different niches, facilitating their dissemination. Toxoplasma gondii tachyzoites divide using a unique form of cell division called endodyogeny. This process involves a single round of DNA replication, closed nuclear mitosis, and assembly of two daughter cells within a mother. In higher Eukaryotes, the four-subunit chromosomal passenger complex (CPC) (Aurora kinase B (ARKB)/INCENP/Borealin/Survivin) promotes chromosome bi-orientation by detaching incorrect kinetochore-microtubule attachments, playing an essential role in controlling cell division fidelity. Herein, we report the characterization of the Toxoplasma CPC (Aurora kinase 1 (Ark1)/INCENP1/INCENP2). We show that the CPC exhibits dynamic localization in a cell cycle-dependent manner. TgArk1 interacts with both TgINCENPs, with TgINCENP2 being essential for its translocation to the nucleus. While TgINCENPl appears to be dispensable, interfering with TgArk1 or TgINCENP2 results in pronounced division and growth defects. Significant anti-cancer drug development efforts have focused on targeting human ARKB. Parasite treatment with low doses of hesperadin, a known inhibitor of human ARKB at higher concentrations, phenocopies the TgArk1 and TgINCENP2 mutants. Overall, our study provides new insights into the mechanisms underpinning cell cycle control in Apicomplexa, and highlights TgArk1 as potential drug target.

Toxoplasma gondii is a parasitic protist possessing a limited set of proteins involved in the autophagy pathway, a self-degradative machinery for protein and organelle recycling. This distant eukaryote has even repurposed part of this machinery, centered on protein ATG8, for a non-degradative function related to the maintenance of the apicoplast, a parasite-specific organelle. However, some evidence also suggest Toxoplasma is able to generate autophagic vesicles upon stress, and that some autophagy-related proteins, such as ATG9, might be involved solely in the canonical autophagy function. Here, we have characterised two Toxoplasma proteins containing WD-40 repeat that can bind lipids for their recruitment to vesicular structures upon stress. They belong to the PROPPIN family and are homologues to ATG18/WIPI, which are known to be important for the autophagic process. We conducted a functional analysis of these two Toxoplasma PROPPINs. One of them is dispensable for normal in vitro growth, although it may play a role for parasite survival in specific stress conditions or for parasite fitness in the host, through a canonical autophagy-related function. The other, however, seems important for parasite viability in normal growth conditions and could be primarily involved in a non-canonical function. These divergent roles for two proteins from the same family illustrate the functional versatility of the autophagy-related machinery in Toxoplasma.

Summary Apicomplexan parasites harbour unique secretory organelles (dense granules, rhoptries and micronemes) that play essential functions in host infection. Toxoplasma gondii parasites seem to possess an atypical endosome-like compartment, which contains an assortment of proteins that appear to be involved in vesicular sorting and trafficking towards secretory organelles. Recent studies highlighted the essential roles of many regulators such as Rab5A, Rab5C, sortilin-like receptor and syntaxin-6 in secretory organelle biogenesis. However, little is known about the protein complexes that recruit Rab-GTPases and SNAREs for membrane tethering in Apicomplexa. In mammals and yeast, transport, tethering and fusion of vesicles from early endosomes to lysosomes and the vacuole, respectively, are mediated by CORVET and HOPS complexes, both built on the same Vps-C core that includes Vps11 protein. Here, we show that a T. gondii Vps11 orthologue is essential for the biogenesis or proper subcellular localization of secretory organelle proteins. TgVps11 is a dynamic protein that associates with Golgi endosomal-related compartments, the vacuole and immature apical secretory organelles. Conditional knock-down of TgVps11 disrupts biogenesis of dense granules, rhoptries and micronemes. As a consequence, parasite motility, invasion, egress and intracellular growth are affected. This phenotype was confirmed with additional knock-down mutants of the HOPS complex. In conclusion, we show that apicomplexan parasites use canonical regulators of the endolysosome system to accomplish essential parasite-specific functions in the biogenesis of their unique secretory organelles.

Summary Phosphoinositides regulate numerous cellular processes by recruiting cytosolic effector proteins and acting as membrane signalling entities. The cellular metabolism and localization of phosphoinositides are tightly regulated by distinct lipid kinases and phosphatases. Here, we identify and characterize a unique phosphatidylinositol 3 kinase (PI3K) in Toxoplasma gondii, a protozoan parasite belonging to the phylum Apicomplexa. Conditional depletion of this enzyme and subsequently of its product, PI(3)P, drastically alters the morphology and inheritance of the apicoplast, an endosymbiotic organelle of algal origin that is a unique feature of many Apicomplexa. We searched the T. gondii genome for PI(3)P-binding proteins and identified in total six PX and FYVE domain-containing proteins including a PIKfyve lipid kinase, which phosphorylates PI(3)P into PI(3,5)P2. Although depletion of putative PI(3)P-binding proteins shows that they are not essential for parasite growth and apicoplast biology, conditional disruption of PIKfyve induces enlarged apicoplasts, as observed upon loss of PI(3)P. A similar defect of apicoplast homeostasis was also observed by knocking down the PIKfyve regulatory protein ArPIKfyve, suggesting that in T. gondii, PI(3)P-related function for the apicoplast might mainly be to serve as a precursor for the synthesis of PI(3,5)P2. Accordingly, PI3K is conserved in all apicomplexan parasites whereas PIKfyve and ArPIKfyve are absent in Cryptosporidium species that lack an apicoplast, supporting a direct role of PI(3,5)P2 in apicoplast homeostasis. This study enriches the already diverse functions attributed to PI(3,5)P2 in eukaryotic cells and highlights these parasite lipid kinases as potential drug targets.

Apicomplexan parasites express various calcium-dependent protein kinases (CDPKs), and some of them play essential roles in invasion and egress. Five of the six CDPKs conserved in most Apicomplexa have been studied at the molecular and cellular levels in Plasmodium species and/or in Toxoplasma gondii parasites, but the function of CDPK7 was so far uncharacterized. In T. gondii, during intracellular replication, two parasites are formed within a mother cell through a unique process called endodyogeny. Here we demonstrate that the knock-down of CDPK7 protein in T. gondii results in pronounced defects in parasite division and a major growth deficiency, while it is dispensable for motility, egress and microneme exocytosis. In cdpk7-depleted parasites, the overall DNA content was not impaired, but the polarity of daughter cells budding and the fate of several subcellular structures or proteins involved in cell division were affected, such as the centrosomes and the kinetochore. Overall, our data suggest that CDPK7 is crucial for proper maintenance of centrosome integrity required for the initiation of endodyogeny. Our findings provide a first insight into the probable role of calcium-dependent signalling in parasite multiplication, in addition to its more widely explored role in invasion and egress.

Apicomplexan parasites employ gliding motility that depends on the polymerization of parasite actin filaments for host cell entry. Despite this requirement, parasite actin remains almost entirely unpolymerized at steady state; formation of filaments required for motility relies on a small repertoire of actin-binding proteins. Previous studies have shown that apicomplexan formins and profilin exhibit canonical functions on heterologous actins from higher eukaryotes; however, their biochemical properties on parasite actins are unknown. We therefore analyzed the impact of T. gondii profilin (TgPRF) and FH1-FH2 domains of two formin isoforms in T. gondii (TgFRM1 and TgFRM2) on the polymerization of T. gondii actin (TgACTI). Our findings based on in vitro assays demonstrate that TgFRM1-FH1-FH2 and TgFRM2-FH1-FH2 dramatically enhanced TgACTI polymerization in the absence of profilin, making them the sole protein factors known to initiate polymerization of this normally unstable actin. In addition, T. gondii formin domains were shown to both initiate polymerization and induce bundling of TgACTI filaments; however, they did not rely on TgPRF for these activities. In contrast, TgPRF sequestered TgACTI monomers, thus inhibiting polymerization even in the presence of formins. Collectively, these findings provide insight into the unusual control mechanisms of actin dynamics within the parasite.

We have characterized the Toxoplasma gondii protein phosphatase type 1 (TgPP1) and a potential regulatory binding protein belonging to the leucine-rich repeat protein family, designated TgLRR1. TgLRR1 is capable of binding to TgPP1 to inhibit its activity and to override a G 2 /M cell cycle checkpoint in Xenopus oocytes. In the parasite, TgLRR1 mRNA and protein are both highly expressed in the rapidly replicating and virulent tachyzoites, while only low levels are detected in the slowly dividing and quiescent bradyzoites. TgPP1 mRNA and protein levels are equally abundant in tachyzoites and bradyzoites. Affinity pull down and immunoprecipitation experiments reveal that the TgLRR1-TgPP1 interaction takes place in the nuclear subcompartment of tachyzoites. These results are consistent with those of localization studies using both indirect immunofluorescence with specific polyclonal antibody and transient transfection of T. gondii vector expressing TgLRR1 and TgPP1. The inability to obtain stable transgenic tachyzoites suggested that overexpression of TgLRR1 and TgPP1 may impair the parasite's growth. Together with the activation of Xenopus oocyte meiosis reinitiation, these data indicate that TgLRR1 protein could play a role in the regulation of the T. gondii cell cycle through the modulation of phosphatase activity.

Apicomplexans use the endolysosomal system for the biogenesis of their secretory organelles, namely, micronemes, rhoptries, and dense granules. In Toxoplasma gondii, our previous in silico search identified the HOPS tethering but not the CORVET complex and demonstrated a role of Vps11 (a common component for both complexes) in its secretory organelle biogenesis. Herein, we performed Vps11-GFP-Trap pull-down assays and identified by proteomic analysis, not only the CORVET-specific subunit Vps8 but also a BEACH domain-containing protein (BDCP) conserved in eukaryotes. We show that knocking-down Vps8 affects targeting of dense granule proteins, transport of rhoptry proteins, and the localization of the cathepsin L protease vacuolar compartment marker. Only a subset of micronemal proteins are affected by the absence of Vps8, shedding light on at least two trafficking pathways involved in microneme maturation. Knocking-down BDCP revealed a restricted and particular role of this protein in rhoptry and vacuolar compartment biogenesis. Moreover, depletion of BDCP or Vps8 abolishes parasite virulence in vivo. This study identified BDCP as a novel CORVET/HOPS-associated protein, playing specific roles and acting in concert during secretory organelle biogenesis, an essential process for host cell infection. Our results open the hypothesis for a role of BDCP in the vesicular trafficking towards lysosome-related organelles in mammals and yeast.

The invasive forms of apicomplexan parasites share a conserved form of gliding motility that powers parasite migration across biological barriers, host cell invasion and egress from infected cells. Previous studies have established that the duration and direction of gliding motility are determined by actin polymerization; however, regulators of actin dynamics in apicomplexans remain poorly characterized. In the absence of a complete ARP2/3 complex, the formin homology 2 domain containing proteins and the accessory protein profilin are presumed to orchestrate actin polymerization during host cell invasion. Here, we have undertaken the biochemical and functional characterization of two Toxoplasma gondii formins and established that they act in concert as actin nucleators during invasion. The importance of TgFRM1 for parasite motility has been assessed by conditional gene disruption. The contribution of each formin individually and jointly was revealed by an approach based upon the expression of dominant mutants with modified FH2 domains impaired in actin binding but still able to dimerize with their respective endogenous formin. These mutated FH2 domains were fused to the ligand-controlled destabilization domain (DD-FKBP) to achieve conditional expression. This strategy proved unique in identifying the non-redundant and critical roles of both formins in invasion. These findings provide new insights into how controlled actin polymerization drives the directional movement required for productive penetration of parasites into host cells., Author Summary Gliding motility is a unique property of the Apicomplexa. Members of this phylum include important human and animal pathogens. An actomyosin-based machine powers parasite motility and is crucial for parasite migration across biological barriers, host cell invasion and egress from infected cells. The timing, duration and orientation of the gliding motility are tightly regulated to insure successful establishment of infection. Controlled polymerization of actin filaments is a key feature of motility, and we demonstrate here the implication of two formins that catalyse actin nucleation and fast assembly of filaments. Both proteins are essential and act in concert during productive penetration of the parasite into host cells.

The glideosome is a unique attribute of the Apicomplexa phylum. This myosin-based machine powers parasite motility, migration across biological barriers, host cell invasion and egress from infected cells. The timing, duration and orientation of gliding motility are tightly regulated to assure establishment of infection. Control of glideosome function occurs at several levels. The assembly of the molecular motor complex is governed by posttranslational modifications resulting from a calcium-dependent signalling cascade. The spatially controlled polymerization of actin filaments crucially impacts motility. The relocation of glycolytic enzymes in close proximity of the glideosome may enhance the local production of energy to sustain movement.

Protozoan parasites of the phylum Apicomplexa undergo a lytic cycle whereby a single zoite produced by the previous cycle has to encounter a host cell, invade it, multiply to differentiate into a new zoite generation and escape to resume a new cycle. At every step of this lytic cycle, the cytoskeleton and/or the gliding motility apparatus play a crucial role and recent results have elucidated aspects of these processes, especially in terms of the molecular characterization and interaction of the increasing number of partners involved, and the signalling mechanisms implicated. The present review aims to summarize the most recent findings in the field.

In this paper we examine the real and financial effects of two insiders trading in a static Jain and Mirman model [Jain, N., & Mirman, L. J. (2000). Real and financial effects of insider trading with correlated signals. Economic Theory, 16, 333–353] (henceforth JM). The first insider is the manager of the firm. The second insider is the owner. First, we study the change of the linear-equilibrium variables, in the presence of two insiders. Specifically, we show that the trading order and the real output of the manager are less in this model than in JM model [Jain, N., & Mirman, L. J. (2000). Real and financial effects of insider trading with correlated signals. Economic Theory, 16, 333–353]. Secondly, we show that the stock price reveals more information than in Cournot duopoly and monopoly models studied by Jain and Mirman [Jain, N., & Mirman, L. J. (2000). Real and financial effects of insider trading with correlated signals. Economic Theory, 16, 333–353; Jain, N., & Mirman, L. J. (2002). Effects of insider trading under different market structures. The Quarterly Review of Economics and Finance, 42, 19–39]. Finally, we analyze the comparative statics (insiders' profits) of this model, when the market maker receives one or two signals.

Aurora kinases are eukaryotic serine/threonine protein kinases that regulate key events associated with chromatin condensation, centrosome and spindle function, and cytokinesis. Elucidating the roles of Aurora kinases in apicomplexan parasites is crucial to understand the cell cycle control during Plasmodium schizogony or Toxoplasma endodyogeny. Here, we report on the localization of two previously uncharacterized Toxoplasma Aurora-related kinases (Ark2 and Ark3) in tachyzoites and of the uncharacterized Ark3 orthologue in Plasmodium falciparum erythrocytic stages. In T. gondii, we show that TgArk2 and TgArk3 concentrate at specific sub-cellular structures linked to parasite division: the mitotic spindle and intranuclear mitotic structures (TgArk2), and the outer core of the centrosome and the budding daughter cells cytoskeleton (TgArk3). By tagging the endogenous PfArk3 gene with the green fluorescent protein (GFP) in live parasites, we show that PfArk3 protein expression peaks late in schizogony and localizes at the periphery of budding schizonts. Disruption of the TgArk2 gene reveals no essential function for tachyzoite propagation in vitro, which is surprising giving that the P. falciparum and P. berghei orthologues are essential for erythrocyte schizogony. In contrast, knock-down of TgArk3 protein results in pronounced defects in parasite division and a major growth deficiency. TgArk3-depleted parasites display several defects, such as reduced parasite growth rate, delayed egress and parasite duplication, defect in rosette formation, reduced parasite size and invasion efficiency and lack of virulence in mice. Our study provides new insights into cell cycle control in Toxoplasma and malaria parasites, and highlights Aurora kinase 3 as potential drug target.

Ferroquine (SSR97193) has been shown to be a promising antimalarial, both on laboratory clones and on field isolates. So far, no resistance was documented in Plasmodium falciparum. In the present work, the metabolic pathway of ferroquine, based on experiments using animal and human hepatic models, is proposed. Ferroquine is metabolized mainly via an oxidative pathway into the major metabolite mono-N-demethyl ferroquine and then into di-N,N-demethyl ferroquine. Some other minor metabolic pathways were also identified. Cytochrome P450 isoforms 2C9, 2C19, and 3A4 and, possibly in some patients, isoform 2D6, are mainly involved in ferroquine oxidation. The metabolites were synthesized and tested against the 3D7 (chloroquine-sensitive) and W2 (chloroquine-resistant) P. falciparum strains. According to the results, the activity of the two main metabolites decreased compared with that of ferroquine; however, the activity of the mono-N-demethyl derivative is significantly higher than that of chloroquine on both strains, and the di-N-demethyl derivative remains more active than chloroquine on the chloroquine-resistant strain. These results further support the potential use of ferroquine against human malaria.

Coronins are involved in the regulation of actin dynamics in a multifaceted way, participating in cell migration and vesicular trafficking. Apicomplexan parasites, which exhibit an actin-dependent gliding motility that is essential for traversal through tissues, as well as invasion of and egress from host cells, express only a single coronin, whereas higher eukaryotes possess several isoforms. We set out to characterize the 3-D structure, biochemical function, subcellular localization, and genetic ablation of Toxoplasma gondii coronin (TgCOR), to shed light on its biological role. A combination of X-ray crystallography, small-angle scattering of X-rays, and light scattering revealed the atomic structure of the conserved WD40 domain and the dimeric arrangement of the full-length protein. TgCOR binds to F-actin and increases the rate and extent of actin polymerization. In vivo, TgCOR relocalizes transiently to the posterior pole of motile and invading parasites, independent of actin dynamics, but concomitant to microneme secretory organelle discharge. TgCOR contributes to, but is not essential for, invasion and egress. Taken together, our data point toward a role for TgCOR in stabilizing newly formed, short filaments and F-actin cross-linking, as well as functions linked to endocytosis and recycling of membranes.-Salamun, J., Kallio, J. P., Daher, W., Soldati-Favre, D., Kursula, I. Structure of Toxoplasma gondii coronin, an actin-binding protein that relocalizes to the posterior pole of invasive parasites and contributes to invasion and egress.

Phosphoinositides regulate numerous cellular processes, by recruiting cytosolic effector proteins and acting as membrane signaling entities. The cellular metabolism and localization of phosphoinositides are tightly regulated by distinct lipid kinases and phosphatases. Here, we identify and characterize a unique phosphatidylinositol 3-Kinase (PI3K) in Toxoplasma gondii, a protozoan parasite belonging to the phylum Apicomplexa. Conditional depletion of this enzyme and subsequently of its product, PI(3)P, drastically alters the morphology and inheritance of the apicoplast, an endosymbiontic organelle of algal origin that is a unique feature of many Apicomplexa. We searched the T. gondii genome for PI(3)P binding proteins and identified in total six PX and FYVE-domain containing proteins including a PIKfyve lipid kinase, which phosphorylates PI(3)P into PI(3,5)P2. While depletion of putative PI(3)P binding proteins shows that they are not essential for parasite growth and apicoplast biology, conditional disruption of PIKfyve induces enlarged apicoplasts, as observed upon the loss of PI(3)P. A similar defect of apicoplast homeostasis was also observed by knocking-down the PIKfyve regulatory protein ArPIKfyve, suggesting that in T. gondii, PI(3)P-related function for the apicoplast might mainly be to serve as a precursor for the synthesis of PI(3,5)P2. Accordingly, PI3K is conserved in all apicomplexan parasites whereas PIKfyve and ArPIKfyve are absent in Cryptosporidium species which lack an apicoplast, supporting a direct role of PI(3,5)P2 in apicoplast homeostasis. This study enriches the already diverse functions attributed to PI(3,5)P2 in eukaryotic cells and highlights these parasite lipid kinases as potential drug targets.

Background Ferroquine (FQ), or SSR97193, is a novel antimalarial drug currently in phase I clinical trials. FQ is a unique organometallic compound designed to overcome the chloroquine (CQ) resistance problem. FQ revealed to be equally active on CQ-sensitive and CQ-resistant Plasmodium falciparum laboratory strains and field isolates. FQ is also curative on rodent malaria parasites. As FQ will be tested in patients, the potential for resistance to this drug was evaluated. Methods The relationship between CQ-resistant transporter gene genotype and susceptibility to FQ were studied in 33 Cambodian P. falciparum field isolates previously studied for their in vitro response to CQ. In parallel, the ability of the CQ-resistant strain W2, to become resistant to FQ under drug pressure was assessed. Results The IC50 values for FQ in field isolates were found to be unrelated to mutations occurring in the P. falciparum chloroquine resistance transporter (PfCRT) or to the level of expression of the corresponding mRNA. In vitro, under a drug pressure of 100 nM of FQ, transient survival was observed in only one of two experiments. Conclusion Field isolates studies and experimental drug pressure experiments showed that FQ overcomes CQ resistance, which reinforces the potential of this compound as a new antimalarial drug.

In the process of autophagy, the Atg8 protein is conjugated, through a ubiquitin-like system, to the lipid phosphatidylethanolamine (PE) to associate with the membrane of forming autophagosomes. There, it plays a crucial role in the genesis of these organelles and in autophagy in general. In most eukaryotes, the cysteine peptidase Atg4 processes the C terminus of cytosolic Atg8 to regulate its association with autophagosomal membranes and also delipidates Atg8 to release this protein from membranes. The parasitic protist Toxoplasma gondii contains a functional, yet apparently reduced, autophagic machinery. T. gondii Atg8 homolog, in addition to a cytosolic and occasionally autophagosomal localization, also localizes to the apicoplast, a nonphotosynthetic plastid bounded by four membranes. Our attempts to interfere with TgATG8 function showed that it appears to be essential for parasite multiplication inside its host cell. This protein also displays a peculiar C terminus that does not seem to necessitate processing prior to membrane association and yet an unusually large Toxoplasma homolog of ATG4 is predicted in the parasite genome. A TgATG4 conditional expression mutant that we have generated is severely affected in growth, and displays significant alterations at the organellar level, noticeably with a fragmentation of the mitochondrial network and a loss of the apicoplast. TgATG4-depleted parasites appear to be defective in the recycling of membrane-bound TgATG8. Overall, our data highlight a role for the TgATG8 conjugation pathway in maintaining the homeostasis of the parasite's organelles and suggest that Toxoplasma has evolved a specialized autophagic machinery with original regulation.

Members of the Apicomplexa phylum possess an organelle surrounded by four membranes, originating from the secondary endosymbiosis of a red alga. This so-called apicoplast hosts essential metabolic pathways. We report here that apicoplast inheritance is an actin-based process. Concordantly, parasites depleted in either profilin or actin depolymerizing factor, or parasites overexpressing the FH2 domain of formin 2, result in loss of the apicoplast. The class XXII myosin F (MyoF) is conserved across the phylum and localizes in the vicinity of the Toxoplasma gondii apicoplast during division. Conditional knockdown of TgMyoF severely affects apicoplast turnover, leading to parasite death. This recapitulates the phenotype observed upon perturbation of actin dynamics that led to the accumulation of the apicoplast and secretory organelles in enlarged residual bodies. To further dissect the mode of action of this motor, we conditionally stabilized the tail of MyoF, which forms an inactive heterodimer with endogenous TgMyoF. This dominant negative mutant reveals a central role of this motor in the positioning of the two centrosomes prior to daughter cell formation and in apicoplast segregation.

In this paper, we analyze the effect of Cournot competition with differentiated products on the real and financial decisions of a publicly-owned firm, with three different structures in the financial market : monopoly, duopoly and Stackelberg. We shows that the degree of product differentiation does not affect the results found in the literature on insider trading, concerning the effect of the financial market structure on firms' outputs, the revelation of information and the insiders' orders. Besides, firms' output, the amount of information revealed in the stock price, the insiders' trading orders and the owners' profits are independent of the degree of product differentiation. The real market structure through the degree of product differentiation is found to determine the level of the compensation scheme earned by the manager, the market makers' response to the total order flow signal as well as the managers' profits., Ce papier analyse l'effet de la concurrence à la Cournot avec différentiation de produits, sur les décisions financières et réelles d'une entreprise publique, sous trois structures du marché financier : monopole, duopole et concurrence à la Stackelberg. Les résultats montrent que l'effet de la structure du marché financier sur les quantités produites par les firmes, la révélation d'information, les actions des initiés ainsi que les profits des propriétaires de la firme, est invariant avec différentiation de produits. En revanche, cette structure a un effet direct sur la compensation du manager, ses profits et sur un des coefficients du prix du marché financier.

Toxoplasma gondii belongs to the phylum Apicomplexa, a group of obligate intracellular parasites that rely on gliding motility to enter host cells. Drugs interfering with the actin cytoskeleton block parasite motility, host cell invasion, and egress from infected cells. Myosin A, profilin, formin 1, formin 2, and actin-depolymerizing factor have all been implicated in parasite motility, yet little is known regarding the importance of actin polymerization and other myosins for the remaining steps of the parasite lytic cycle. Here we establish that T. gondii formin 3 (TgFRM3), a newly described formin homology 2 domain (FH2)-containing protein, binds to Toxoplasma actin and nucleates rabbit actin assembly in vitro . TgFRM3 expressed as a transgene exhibits a patchy localization at several distinct structures within the parasite. Disruption of the TgFRM3 gene by double homologous recombination in a ku80-ko strain reveals no vital function for tachyzoite propagation in vitro , which is consistent with its weak level of expression in this life stage. Conditional stabilization of truncated forms of TgFRM3 suggests that different regions of the molecule contribute to distinct localizations. Moreover, expression of TgFRM3 lacking the C-terminal domain severely affects parasite growth and replication. This work provides a first insight into how this specialized formin, restricted to the group of coccidia, completes its actin-nucleating activity.