Invasion factors are coupled to key signalling events leading to the establishment of infection in apicomplexan parasites

Label-free quantitative detection and comparative analysis of lysine acetylation during the different life stages of Eimeria tenella

Proteome-wide lysine acetylation has been documented in apicomplexan parasite Toxoplasma gondii and Plasmodium falciparum. Here, we conducted the first lysine acetylome in unsporulated oocysts (USO), sporulated 7 h oocysts (SO 7h), sporulated oocysts (SO), sporozoites (S), and the second generation merozoites (SMG) of Eimeria tenella through a 4D label-free quantitative technique. Altogether, 8532 lysine acetylation sites on 2325 proteins were identified in E. tenella, among which 5445 sites on 1493 proteins were quantified. In addition, 557, 339, 478, 248, 241, and 424 differentially expressed proteins were identified in the comparisons SO7h vs USO, SO vs SO7h, SO vs USO, S vs SO, SMG vs S, and USO vs SMG, respectively. The bioinformatics analysis of the acetylome showed that the lysine acetylation is widespread on proteins of diverse functions. Moreover, the dynamic changes of lysine acetylome among E. tenella different life stages revealed significant regulation during the whole process of E. tenella growth and stage conversion. This study provides a beginning for the investigation of the regulate role of lysine acetylation in E. tenella and may provide new strategies for anticoccidiosis drug and vaccine development. Raw data are publicly available at iProX with the data set identifier PXD040368.

Recombinant Dense Granule Protein (NcGRA4) Is a Novel Serological Marker for Neospora caninum Infection in Goats

Neospora caninum is widely recognised as one of the most significant causes of abortion in cattle, with infections also occurring in sheep and goats. To prevent and control animal neosporosis, it is crucial to develop sensitive and specific methods for detecting N. caninum infection. Recently, several recombinant proteins have been utilised in serological assays for the diagnosis of neosporosis. In this study, we used commercial gene synthesis to produce dense granular antigen 4 (NcGRA4) recombinant protein. NcGRA4 plasmids were expressed in the Escherichia coli system and then purified. The purified recombinant protein was analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. To evaluate the diagnostic potential of recombinant NcGRA4 protein, we tested 214 serum samples from goat farms via indirect enzyme-linked immunosorbent assay (iELISA) and compared the results to those from the indirect fluorescent antibody test (IFAT). Western blotting analysis revealed a single NcGRA4 band with an expected molecular weight of 32 kDa. The specific IgG against N. caninum was detected in 34.1% and 35% of samples evaluated by NcGRA4 iELISA and IFAT, respectively. The sensitivity and specificity of the NcGRA4 iELISA were 71.6% and 86.3%, respectively, when compared with the results from IFAT. Our results demonstrate that a recombinant protein that can be used to detect animal neosporosis can be produced using a synthetic NcGRA4 gene. Overall, recombinant NcGRA4 shows promise as a sensitive and specific serological marker for identifying target IgG in goat samples.

Cryo-tomography reveals rigid-body motion and organization of apicomplexan invasion machinery

The apical complex is a specialized collection of cytoskeletal and secretory machinery in apicomplexan parasites, which include the pathogens that cause malaria and toxoplasmosis. Its structure and mechanism of motion are poorly understood. We used cryo-FIB-milling and cryo-electron tomography to visualize the 3D-structure of the apical complex in its protruded and retracted states. Averages of conoid-fibers revealed their polarity and unusual nine-protofilament arrangement with associated proteins connecting and likely stabilizing the fibers. Neither the structure of the conoid-fibers nor the architecture of the spiral-shaped conoid complex change during protrusion or retraction. Thus, the conoid moves as a rigid body, and is not spring-like and compressible, as previously suggested. Instead, the apical-polar-rings (APR), previously considered rigid, dilate during conoid protrusion. We identified actin-like filaments connecting the conoid and APR during protrusion, suggesting a role during conoid movements. Furthermore, our data capture the parasites in the act of secretion during conoid protrusion.

Calcium in the Backstage of Malaria Parasite Biology

The calcium ion (Ca2+) is a ubiquitous second messenger involved in key biological processes in prokaryotes and eukaryotes. In Plasmodium species, Ca2+ signaling plays a central role in the parasite life cycle. It has been associated with parasite development, fertilization, locomotion, and host cell infection. Despite the lack of a canonical inositol-1,4,5-triphosphate receptor gene in the Plasmodium genome, pharmacological evidence indicates that inositol-1,4,5-triphosphate triggers Ca2+ mobilization from the endoplasmic reticulum. Other structures such as acidocalcisomes, food vacuole and mitochondria are proposed to act as supplementary intracellular Ca2+ reservoirs. Several Ca2+-binding proteins (CaBPs) trigger downstream signaling. Other proteins with no EF-hand motifs, but apparently involved with CaBPs, are depicted as playing an important role in the erythrocyte invasion and egress. It is also proposed that a cross-talk among kinases, which are not members of the family of Ca2+-dependent protein kinases, such as protein kinases G, A and B, play additional roles mediated indirectly by Ca2+ regulation. This statement may be extended for proteins directly related to invasion or egress, such as SUB1, ERC, IMC1I, IMC1g, GAP45 and EBA175. In this review, we update our understanding of aspects of Ca2+-mediated signaling correlated to the developmental stages of the malaria parasite life cycle.

Toxoplasma gondii ROP17 promotes autophagy via the Bcl-2-Beclin 1 pathway

The apicomplexan Toxoplasma gondii (Nicolle et Manceaux, 1908) secretes a group of serine/threonine kinases from rhoptries, which play vital roles in boosting intracellular infection. Toxoplasma gondii rhoptry organelle protein 17 (ROP17) is one of these important kinase proteins. Nevertheless, its function remains unclear. Here, we showed that ROP17 induced autophagy in vitro and in vivo. The autophagy of small intestine tissues of T. gondii tachyzoite (RH strain)-infected mice was detected by the immunohistochemistry staining of LC3B, Beclin 1 and P62. ROP17 overexpression augmented starvation-induced autophagy in HEK 293T cells as measured by MDC staining, transmission electron microscopy (TEM), fluorescence microscopy and Western blot analysis. Moreover, the interaction of ROP17 and Bcl-2 was confirmed using co-immunoprecipitation analysis, and the data demonstrated that ROP17 had an autophagic role dependent on the Beclin 1-Bcl-2 pathway, which was also revealed in an in vivo model through immunohistochemical staining. Pearson coefficient analysis showed that there existed strong positive correlations between the expression of ROP17 and LC3B, Beclin 1 and phosphorylation of Bcl-2, while strong negative correlations between the expression of ROP17 and p62 and Bcl-2. Collectively, our findings indicate that ROP17 plays a pivotal role in maintaining T. gondii proliferation in host cells via the promotion of autophagy-dependent survival.

Diverse Roles of TgMIC1/4/6 in the Toxoplasma Infection

Toxoplasma gondii microneme is a specialized secretory organelle that discharges its contents at the apical tip of this apicomplexan parasite in a sequential and regulated manner. Increasing number of studies on microneme proteins (MICs) have shown them as a predominant and important role in host cell attachment, invasion, motility and pathogenesis. In this review, we summarize the research advances in one of the most important MICs complexes, TgMIC1/4/6, which will contribute to improve the understanding of the molecular mechanism of T. gondii infection and provide a theoretical basis for the effective control against T. gondii.

Global transcriptome landscape of the rabbit protozoan parasite Eimeria stiedae

Background

Coccidiosis caused by Eimeria stiedae is a widespread and economically significant disease of rabbits. The lack of studies on the life-cycle development and host interactions of E. stiedae at the molecular level has hampered our understanding of its pathogenesis.

Methods

In this study, we present a comprehensive transcriptome landscape of E. stiedae to illustrate its dynamic development from unsporulated oocysts to sporulated oocysts, merozoites, and gametocytes, and to identify genes related to parasite-host interactions during parasitism using combined PacBio single-molecule real-time and Illumina RNA sequencing followed by bioinformatics analysis and qRT-PCR validation.

Results

In total, 12,582 non-redundant full-length transcripts were generated with an average length of 1808 bp from the life-cycle stages of E. stiedae. Pairwise comparisons between stages revealed 8775 differentially expressed genes (DEGs) showing highly significant description changes, which compiled a snapshot of the mechanisms underlining asexual and sexual biology of E. stiedae including oocyst sporulation between unsporulated and sporulated oocysts; merozoite replication between sporulated oocysts and merozoites; and gametophyte development and gamete generation between merozoites and gametocytes. Further, 248 DEGs were grouped into nine series clusters and five groups by expression patterns, and showed that parasite–host interaction-related genes predominated in merozoites and gametocytes and were mostly involved in steroid biosynthesis and lipid metabolism and carboxylic acid. Additionally, co-expression analyses identified genes associated with development and host invasion in unsporulated and sporulated oocysts and immune interactions during gametocyte parasitism.

Conclusions

This is the first study, to our knowledge, to use the global transcriptome profiles to decipher molecular changes across the E. stiedae life cycle, and these results not only provide important information for the molecular characterization of E. stiedae, but also offer valuable resources to study other apicomplexan parasites with veterinary and public significance.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04811-5.

Characterization of Neospora Caninum Microneme Protein 26 and Its Potential Use as a Diagnostic Marker for Neosporosis in Cattle

The apicomplexan parasite Neospora caninum causes neosporosis, an illness that leads to abortion or stillbirth in cattle, causing massive economic losses to the livestock industry. Rapid and viable diagnosis is the premise of prevention and control for neosporosis. In this study, we screened a new microneme protein 26 (NcMIC26) through western blot and mass spectrometry identification from the excretory secretion antigen (ESA) of N. caninum tachyzoites. NcMIC26 is subcellularly localized to the microneme of parasites. NcMIC26 is a specific antigen of N. caninum and has no cross-reaction with Toxoplasma gondii. Therefore, NcMIC26 has the potential to be a candidate diagnostic antigen for neosporosis. To test this hypothesis, recombinant NcMIC26 (rNcMIC26) was expressed in Escherichia coli (E. coli), and an indirect ELISA for detecting anti-N. caninum antibodies in cattle was established. Compared with that of the indirect immunofluorescent antibody test (IFAT), the positive coincidence rate of the ELISA based on rNcMIC26 was 76.53% (75/98), which was higher than that of an ELISA based on rSRS2 (66.33%), and the negative coincidence rate was 84.62% (33/39). It is noteworthy that 30 positive samples confirmed by IFAT were consistent with the rNcMIC26 ELISA but were negative by the rNcSRS2 ELISA. Our research illustrated that NcMIC26 is a dependable diagnostic marker for the serodiagnosis of N. caninum infection in cattle and could be utilized as a supplementary antigen for missed detection by NcSRS2.

Pathogenesis of ocular toxoplasmosis

Ocular toxoplasmosis is a retinitis -almost always accompanied by vitritis and choroiditis- caused by intraocular infection with Toxoplasma gondii. Depending on retinal location, this condition may cause substantial vision impairment. T. gondii is an obligate intracellular protozoan parasite, with both sexual and asexual life cycles, and infection is typically contracted orally by consuming encysted bradyzoites in undercooked meat, or oocysts on unwashed garden produce or in contaminated water. Presently available anti-parasitic drugs cannot eliminate T. gondii from the body. In vitro studies using T. gondii tachyzoites, and human retinal cells and tissue have provided important insights into the pathogenesis of ocular toxoplasmosis. T. gondii may cross the vascular endothelium to access human retina by at least three routes: in leukocyte taxis; as a transmigrating tachyzoite; and after infecting endothelial cells. The parasite is capable of navigating the human neuroretina, gaining access to a range of cell populations. Retinal Müller glial cells are preferred initial host cells. T. gondii infection of the retinal pigment epithelial cells alters the secretion of growth factors and induces proliferation of adjacent uninfected epithelial cells. This increases susceptibility of the cells to parasite infection, and may be the basis of the characteristic hyperpigmented toxoplasmic retinal lesion. Infected epithelial cells also generate a vigorous immunologic response, and influence the activity of leukocytes that infiltrate the retina. A range of T. gondii genotypes are associated with human ocular toxoplasmosis, and individual immunogenetics -including polymorphisms in genes encoding innate immune receptors, human leukocyte antigens and cytokines- impacts the clinical manifestations. Research into basic pathogenic mechanisms of ocular toxoplasmosis highlights the importance of prevention and suggests new biological drug targets for established disease.

Clearing or subverting the enemy: Role of autophagy in protozoan infections

The protozoan parasites are evolutionarily divergent, unicellular eukaryotic pathogens representing one of the essential sources of parasitic diseases. These parasites significantly affect the economy and cause public health burdens globally. Protozoan parasites share many cellular features and pathways with their respective host cells. This includes autophagy, a process responsible for self-degradation of the cell's components. There is conservation of the central structural and functional machinery for autophagy in most of the eukaryotic phyla, however, Plasmodium and Toxoplasma possess a decreased number of recognizable autophagy-related proteins (ATG). Plasmodium noticeably lacks clear orthologs of the initiating kinase ATG1/ULK1/2, and both Plasmodium and Toxoplasma lack proteins involved in the nucleation of autophagosomes. These organisms have essential apicoplast, a plastid-like non-photosynthetic organelle, which is an adaptation that is used in penetrating the host cell. Furthermore, available evidence suggests that Leishmania, an intracellular protozoan parasite, induces autophagy in macrophages. The autophagic pathway in Trypanosoma cruzi is activated during metacyclogenesis, a process responsible for the infective forms of parasites. Therefore, numerous pathogens have developed strategies to impair the autophagic mechanism in phagocytes. Regulating autophagy is essential to maintain cellular health as adjustments in the autophagy pathway have been linked to the progression of several physiological and pathological conditions in humans. In this review, we report current advances in autophagy in parasites and their host cells, focusing on the ramifications of these studies in the design of potential anti-protozoan therapeutics.

Interplay Between Toxoplasma gondii, Autophagy, and Autophagy Proteins

Survival of Toxoplasma gondii within host cells depends on its ability of reside in a vacuole that avoids lysosomal degradation and enables parasite replication. The interplay between immune-mediated responses that lead to either autophagy-driven lysosomal degradation or disruption of the vacuole and the strategies used by the parasite to avoid these responses are major determinants of the outcome of infection. This article provides an overview of this interplay with an emphasis on autophagy.

A plasma membrane localized protein phosphatase in Toxoplasma gondii, PPM5C, regulates attachment to host cells

The propagation of Toxoplasma gondii is accomplished by repeated lytic cycles of parasite attachment to a host cell, invasion, replication within a parasitophorous vacuole, and egress from the cell. This lytic cycle is delicately regulated by calcium-dependent reversible phosphorylation of the molecular machinery that drives invasion and egress. While much progress has been made elucidating the protein kinases and substrates central to parasite propagation, little is known about the relevant protein phosphatases. In this study, we focused on the five protein phosphatases that are predicted to be membrane-associated either integrally or peripherally. We have determined that of these only PPM5C, a PP2C family member, localizes to the plasma membrane of Toxoplasma. Disruption of PPM5C results in a slow propagation phenotype in tissue culture. Interestingly, parasites lacking PPM5C divide and undergo egress at a normal rate, but have a deficiency in attaching to host cells. Both membrane localization and phosphatase activity are required for PPM5C’s role in attachment. Phosphoproteomic analysis show relatively few phosphorylation sites being affected by PPM5C deletion in extracellular parasites of which several are found on proteins involved in signaling cascades. This implies that PPM5C is part of a wider regulatory network important for attachment to host cells.

Structural Basis of Phosphatidic Acid Sensing by APH in Apicomplexan Parasites

Plasmodium falciparum and Toxoplasma gondii are obligate intracellular parasites that belong to the phylum of Apicomplexa and cause major human diseases. Their access to an intracellular lifestyle is reliant on the coordinated release of proteins from the specialized apical organelles called micronemes and rhoptries. A specific phosphatidic acid effector, the acylated pleckstrin homology domain-containing protein (APH) plays a central role in microneme exocytosis and thus is essential for motility, cell entry, and egress. TgAPH is acylated on the surface of the micronemes and recruited to phosphatidic acid (PA)-enriched membranes. Here, we dissect the atomic details of APH PA-sensing hub and its functional interaction with phospholipid membranes. We unravel the key determinant of PA recognition for the first time and show that APH inserts into and clusters multiple phosphate head-groups at the bilayer binding surface.

Identification of an interaction between calcium-dependent protein kinase 4 (EtCDPK4) and serine protease inhibitor (EtSerpin) in Eimeria tenella

Background

Eimeria tenella is an obligate intracellular apicomplexan protozoan parasite that has a complex life-cycle. Calcium ions, through various calcium-dependent protein kinases (CDPKs), regulate key events in parasite growth and development, including protein secretion, movement, differentiation, and invasion of and escape from host cells. In this study, we identified proteins that interact with EtCDPK4 to lay a foundation for clarifying the role of CDPKs in calcium channels.

Methods

Eimeria tenella merozoites were collected to construct a yeast two-hybrid (Y2H) cDNA library. The Y2H system was used to identify proteins that interact with EtCDPK4. One of interacting proteins was confirmed using bimolecular fluorescence complementation and co-immunoprecipitation in vivo. Co-localization of proteins was performed using immunofluorescence assays.

Results

Eight proteins that interact with EtCDPK4 were identified using the Y2H system. One of the proteins, E. tenella serine protease inhibitor 1 (EtSerpin), was further confirmed.

Conclusion

In this study, we screened for proteins that interact with EtCDPK4. An interaction between EtSerpin and EtCDPK4 was identified that may contribute to the invasion and development of E. tenella in host cells.

Toxoplasma gondii induces FAK-Src-STAT3 signaling during infection of host cells that prevents parasite targeting by autophagy

Targeting of Toxoplasma gondii by autophagy is an effective mechanism by which host cells kill the protozoan. Thus, the parasite must avoid autophagic targeting to survive. Here we show that the mammalian cytoplasmic molecule Focal Adhesion Kinase (FAK) becomes activated during invasion of host cells. Activated FAK appears to accompany the formation of the moving junction (as assessed by expression the parasite protein RON4). FAK activation was inhibited by approaches that impaired β1 and β3 integrin signaling. FAK caused activation of Src that in turn mediated Epidermal Growth Factor Receptor (EGFR) phosphorylation at the unique Y845 residue. Expression of Src-resistant Y845F EGFR mutant markedly inhibited ROP16-independent activation of STAT3 in host cells. Activation of FAK, Y845 EGFR or STAT3 prevented activation of PKR and eIF2α, key stimulators of autophagy. Genetic or pharmacologic inhibition of FAK, Src, EGFR phosphorylation at Y845, or STAT3 caused accumulation of the autophagy protein LC3 and LAMP-1 around the parasite and parasite killing dependent on autophagy proteins (ULK1 and Beclin 1) and lysosomal enzymes. Parasite killing was inhibited by expression of dominant negative PKR. Thus, T. gondii activates a FAK→Src→Y845-EGFR→STAT3 signaling axis within mammalian cells, thereby enabling the parasite to survive by avoiding autophagic targeting through a mechanism likely dependent on preventing activation of PKR and eIF2α.

Transcriptome modulation of bovine trophoblast cells in vitro by Neospora caninum

Neospora caninum is one of the most efficient transplacentally transmitted pathogens in cattle and is a cause of abortion in this domestic species. The invasion and proliferation of Neospora caninum in the placenta and its dissemination to the foetus are crucial events in the outcome of an infection. In the bovine placenta, the placentomes are formed by maternal caruncles, which are delimited by a maternal epithelium and foetal cotyledons, which are delimited by an epithelial layer named the trophoblast. These epithelia form a physical barrier against foetal infection. Furthermore, trophoblast cells act as an innate immune defence at the foetal-maternal interface. Neospora caninum invades and proliferates in trophoblast cells in vitro, but it is unknown whether host cell modulation events, which affect the immune response and other processes in the trophoblast, occur. In this work, we investigated the transcriptomic modulation by Neospora caninum infection in the bovine trophoblast cell line F3. In addition, two Neospora caninum isolates with marked differences in virulence, Nc-Spain1H and the Nc-Spain7, were used in this study to investigate the influence of these isolates in F3 modulation. The results showed a clear influence on extracellular matrix reorganisation, cholesterol biosynthesis and the transcription factor AP-1 network. Interestingly, although differences in the transcriptome profiles induced by each isolate were observed, specific isolate-modulated processes were not identified, suggesting very similar regulation in both isolates. Differential expression of the N. caninum genes between both isolates was also investigated. Genes involved in host cell attachment and invasion (SAG-related and microneme proteins), glideosome, rhoptries, metabolic processes, cell cycle and stress response were differentially expressed between the isolates, which could explain their variability. This study provides a global view of Neospora caninum interactions with bovine trophoblast cells and of the intra-specific differences between two Neospora caninum isolates with biological differences.

Vacuolar protein sorting mechanisms in apicomplexan parasites

The phylum Apicomplexa comprises more than 5000 species including pathogens of clinical and economical importance. These obligate intracellular parasites possess a highly complex endomembrane system to build amongst others three morphologically distinct secretory organelles: rhoptries, micronemes and dense granules. Proteins released by these organelles are essential for invasion and hijacking of the host cell. Due to the complexity of the internal organization of these parasites, a wide panoply of trafficking factors was expected to be required for the correct sorting of proteins towards the various organelles. However, Toxoplasma gondii and other apicomplexan parasites contain only a core set of these factors and several of the vacuolar protein sorting (VPS) homologues found in most eukaryotes have been lost in this phylum.

In this review, we will summarise our current knowledge about the role of trafficking complexes in T. gondii, highlighting recent studies focused on complexes formed by VPS proteins. We also present a novel, hypothetical model, suggesting the recycling of parasite membrane and micronemal proteins.

Secreted protein kinases regulate cyst burden during chronic toxoplasmosis

Toxoplasma gondii is an apicomplexan parasite that secretes a large number of protein kinases and pseudokinases from its rhoptry organelles. Although some rhoptry kinases (ROPKs) act as virulence factors, many remain uncharacterized. In this study, predicted ROPKs were assessed for bradyzoite expression then prioritized for a reverse genetic analysis in the type II strain Pru that is amenable to targeted disruption. Using CRISPR/Cas9, we engineered C-terminally epitope tagged ROP21 and ROP27 and demonstrated their localization to the parasitophorous vacuole and cyst matrix. ROP21 and ROP27 were not secreted from microneme, rhoptry, or dense granule organelles, but rather were located in small vesicles consistent with a constitutive pathway. Using CRISPR/Cas9, the genes for ROP21, ROP27, ROP28, and ROP30 were deleted individually and in combination, and the mutant parasites were assessed for growth and their ability to form tissue cysts in mice. All knockouts lines were normal for in vitro growth and bradyzoite differentiation, but a combined ∆rop21/∆rop17 knockout led to a 50% reduction in cyst burden in vivo. Our findings question the existing annotation of ROPKs based solely on bioinformatic techniques and yet highlight the importance of secreted kinases in determining the severity of chronic toxoplasmosis.

In Vitro Effect of the Synthetic cal14.1a Conotoxin, Derived from Conus californicus, on the Human Parasite Toxoplasma gondii

Toxins that are secreted by cone snails are small peptides that are used to treat several diseases. However, their effects on parasites with human and veterinary significance are unknown. Toxoplasma gondii is an opportunistic parasite that affects approximately 30% of the world’s population and can be lethal in immunologically compromised individuals. The conventional treatment for this parasitic infection has remained the same since the 1950s, and its efficacy is limited to the acute phase of infection. These findings have necessitated the search for new drugs that specifically target T. gondii. We examined the effects of the synthetic toxin cal14.1a (s-cal14.1a) from C. californicus on the tachyzoite form of T. gondii. Our results indicate that, at micromolar concentrations, s-cal14.1a lowers viability and inhibits host cell invasion (by 50% and 61%, respectively) on exposure to extracellular parasites. Further, intracellular replication decreased significantly while viability of the host cell was unaffected. Our study is the first report on the antiparasitic activity of a synthetic toxin of C. californicus.

Vaccination with Recombinant Microneme Proteins Confers Protection against Experimental Toxoplasmosis in Mice

Toxoplasmosis, a zoonotic disease caused by Toxoplasma gondii, is an important public health problem and veterinary concern. Although there is no vaccine for human toxoplasmosis, many attempts have been made to develop one. Promising vaccine candidates utilize proteins, or their genes, from microneme organelle of T. gondii that are involved in the initial stages of host cell invasion by the parasite. In the present study, we used different recombinant microneme proteins (TgMIC1, TgMIC4, or TgMIC6) or combinations of these proteins (TgMIC1-4 and TgMIC1-4-6) to evaluate the immune response and protection against experimental toxoplasmosis in C57BL/6 mice. Vaccination with recombinant TgMIC1, TgMIC4, or TgMIC6 alone conferred partial protection, as demonstrated by reduced brain cyst burden and mortality rates after challenge. Immunization with TgMIC1-4 or TgMIC1-4-6 vaccines provided the most effective protection, since 70% and 80% of mice, respectively, survived to the acute phase of infection. In addition, these vaccinated mice, in comparison to non-vaccinated ones, showed reduced parasite burden by 59% and 68%, respectively. The protective effect was related to the cellular and humoral immune responses induced by vaccination and included the release of Th1 cytokines IFN-γ and IL-12, antigen-stimulated spleen cell proliferation, and production of antigen-specific serum antibodies. Our results demonstrate that microneme proteins are potential vaccines against T. gondii, since their inoculation prevents or decreases the deleterious effects of the infection.

Insights into anti-parasitism induced by a C-type lectin from Bothrops pauloensis venom on Toxoplasma gondii

Here we evaluate the effects of BpLec, a C-type lectin isolated from Bothrops pauloensis snake venom, on Toxoplasma gondii parasitism. BpLec (0.195-12.5 μg/mL) did not interfere with HeLa (host cell) viability by MTT assay, whereas higher doses decreased viability and changed HeLa morphology. In addition, the host cell treatment before infection did not influence adhesion and proliferation indexes. BpLec did not alter T. gondii tachyzoite viability, as carried out by trypan blue exclusion, but decreased both adhesion and parasite replication, when tachyzoites were treated before infection. Galactose (0.4 M) inhibited the BpLec effect on adhesion assays, suggesting that BpLec probably recognize some glycoconjugate from T. gondii membrane. Additionally, we performed cytokine measurements from supernatants collected from HeLa cells infected with T. gondii tachyzoites previously treated with RPMI or BpLec. MIF and IL-6 productions by HeLa cells were increased by BpLec treatment. Also, TGF-β1 secretion was diminished post-infection, although this effect was not dependent on BpLec treatment. Taken together, our results show that BpLec is capable of reducing T. gondii parasitism after tachyzoite treatment and may represent an interesting tool in the search for parasite antigens involved in these processes.

Identification of host proteins interacting with the integrin-like A domain of Toxoplasma gondii micronemal protein MIC2 by yeast-two-hybrid screening

Background

Toxoplasma gondii is an obligate intracellular protozoan, causing the important zoonosis toxoplasmosis. This parasite utilizes a unique form of locomotion called gliding motility to find and invade host cells. The micronemal adhesin MIC2 plays critical roles in these processes by binding to substrates and host cell receptors using its extracellular adhesive domains. Although MIC2 is known to mediate important interactions between parasites and host cells during invasion, the specific host proteins interacting with MIC2 have not been clearly identified. In this study, we used a yeast-two-hybrid system to search for host proteins that interact with MIC2.

Methods

Different adhesive domains of MIC2 were cloned into the pGBKT7 vector and expressed in fusion with the GAL4 DNA-binding domain as baits. Expression of bait proteins in yeast cells was analyzed by immuno-blotting and their autoactivation was tested via comparison with the pGBKT7 empty vector, which expressed the GAL4 DNA binding-domain only. To identify host proteins interacting with MIC2, a mouse cDNA library cloned into a GAL4 activation-domain expressing vector was screened by yeast-two-hybrid using the integrin-like A domain of MIC2 (residues 74–270) as bait. After initial screening and exclusion of false positive hits, positive preys were sequenced and analyzed using BLAST analysis and Gene Ontology Classifications.

Results

Two host proteins that had not previously been reported to interact with T. gondii MIC2 were identified: they are LAMTOR1 (late endosomal/lysosomal adaptor, MAPK and mTOR activator 1) and RNaseH2B (ribonuclease H2 subunit B). Gene Ontology analysis indicated that these two proteins are associated with many cellular processes, such as lysosome maturation, signaling transduction, and RNA catabolism.

Conclusion

This study is the first one to report interactions between Toxoplasma gondii MIC2 and two host proteins, LAMTOR1 and RNaseH2B. The data will help us to gain a better understanding of the function of MIC2 and suggest that MIC2 may play roles in modulating host signal transduction and other biological processes in addition to binding host cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0543-1) contains supplementary material, which is available to authorized users.

A conserved apicomplexan microneme protein contributes to Toxoplasma gondii invasion and virulence

The obligate intracellular parasite Toxoplasma gondii critically relies on host cell invasion during infection. Proteins secreted from the apical micronemes are central components for host cell recognition, invasion, egress, and virulence. Although previous work established that the sporozoite protein with an altered thrombospondin repeat (SPATR) is a micronemal protein conserved in other apicomplexan parasites, including Plasmodium, Neospora, and Eimeria, no genetic evidence of its contribution to invasion has been reported. SPATR contains a predicted epidermal growth factor domain and two thrombospondin type 1 repeats, implying a role in host cell recognition. In this study, we assess the contribution of T. gondii SPATR (TgSPATR) to T. gondii invasion by genetically ablating it and restoring its expression by genetic complementation. Δspatr parasites were ~50% reduced in invasion compared to parental strains, a defect that was reversed in the complemented strain. In mouse virulence assays, Δspatr parasites were significantly attenuated, with ~20% of mice surviving infection. Given the conservation of this protein among the Apicomplexa, we assessed whether the Plasmodium falciparum SPATR ortholog (PfSPATR) could complement the absence of the TgSPATR. Although PfSPATR showed correct micronemal localization, it did not reverse the invasion deficiency of Δspatr parasites, because of an apparent failure in secretion. Overall, the results suggest that TgSPATR contributes to invasion and virulence, findings that have implications for the many genera and life stages of apicomplexans that express SPATR.

A selective review of advances in coccidiosis research

Coccidiosis is a widespread and economically significant disease of livestock caused by protozoan parasites of the genus Eimeria. This disease is worldwide in occurrence and costs the animal agricultural industry many millions of dollars to control. In recent years, the modern tools of molecular biology, biochemistry, cell biology and immunology have been used to expand greatly our knowledge of these parasites and the disease they cause. Such studies are essential if we are to develop new means for the control of coccidiosis. In this chapter, selective aspects of the biology of these organisms, with emphasis on recent research in poultry, are reviewed. Topics considered include taxonomy, systematics, genetics, genomics, transcriptomics, proteomics, transfection, oocyst biogenesis, host cell invasion, immunobiology, diagnostics and control.

The pathogenesis of malaria: a new perspective

With 3·3 billion people at risk of infection, malaria remains one of the world's most significant health problems. Increasing resistance of the main causative parasite to currently available drugs has created an urgent need to elucidate the pathogenesis of the disease in order to develop new treatments. A possible clue to such an understanding is that the malaria parasite Plasmodium falciparum selectively absorbs vitamin A from the host and appears to use it for its metabolism; serum vitamin A levels are also reduced in children with malaria. Although vitamin A is essential in low concentration for numerous biological functions, higher concentrations are cytotoxic and pro-oxidant, and potentially toxic quantities of the vitamin are stored in the liver. During their life cycle in the host the parasites remain in the liver for several days before invading the red blood cells (RBCs). The hypothesis proposed is that the parasites emerge from the liver packed with vitamin A and use retinoic acid (RA), the main biologically active metabolite of vitamin A, as a cell membrane destabilizer to invade the RBCs throughout the body. The characteristic hemolysis and anemia of malaria and other symptoms of the disease may thus be manifestations of an endogenous form of vitamin A intoxication associated with high concentrations of RA but low concentrations of retinol (ROL). Retinoic acid released from the parasites may also affect the fetus and cause preterm birth and fetal growth restriction (FGR) as a function of the membranolytic and growth inhibitory effects of these compounds, respectively. Subject to testing, the hypothesis suggests that parasite vitamin A metabolism could become a new target for the treatment and prevention of malaria.

Unravelling the Neospora caninum secretome through the secreted fraction (ESA) and quantification of the discharged tachyzoite using high-resolution mass spectrometry-based proteomics

BACKGROUND

The apicomplexan parasite Neospora caninum causes neosporosis, a disease that leads to abortion or stillbirth in cattle, generating an economic impact on the dairy and beef cattle trade. As an obligatory intracellular parasite, N. caninum needs to invade the host cell in an active manner to survive. The increase in parasite cytosolic Ca2+ upon contact with the host cell mediates critical events, including the exocytosis of phylum-specific secretory organelles and the activation of the parasite invasion motor. Because invasion is considered a requirement for pathogen survival and replication within the host, the identification of secreted proteins (secretome) involved in invasion may be useful to reveal interesting targets for therapeutic intervention.

METHODS

To chart the currently missing N. caninum secretome, we employed mass spectrometry-based proteomics to identify proteins present in the N. caninum tachyzoite using two different approaches. The first approach was identifying the proteins present in the tachyzoite-secreted fraction (ESA). The second approach was determining the relative quantification through peptide stable isotope labelling of the tachyzoites submitted to an ethanol secretion stimulus (discharged tachyzoite), expecting to identify the secreted proteins among the down-regulated group.

RESULTS

As a result, 615 proteins were identified at ESA and 2,011 proteins quantified at the discharged tachyzoite. We have analysed the connection between the secreted and the down-regulated proteins and searched for putative regulators of the secretion process among the up-regulated proteins. An interaction network was built by computational prediction involving the up- and down-regulated proteins. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD000424.

CONCLUSIONS

The comparison between the protein abundances in ESA and their measure in the discharged tachyzoite allowed for a more precise identification of the most likely secreted proteins. Information from the network interaction and up-regulated proteins was important to recognise key proteins potentially involved in the metabolic regulation of secretion. Our results may be helpful to guide the selection of targets to be investigated against Neospora caninum and other Apicomplexan organisms.

Toxoplasma gondii antigens recognized by IgG antibodies differ between mice with and without active proliferation of tachyzoites in the brain during the chronic stage of infection

We examined whether tachyzoite proliferation in the brains of immunocompetent hosts during the chronic stage of infection with Toxoplasma gondii induces production of IgG antibodies that recognize parasite antigens different from those recognized by the antibodies of infected hosts that do not have tachyzoite growth. For this purpose, two groups of CBA/J mice, which display continuous tachyzoite growth in their brains during the later stage of infection, were infected, and one group received treatment with sulfadiazine to prevent tachyzoite proliferation during the chronic stage of infection. T. gondii antigens recognized by the IgG antibodies from these two groups of mice were compared using immunoblotting following separation of tachyzoite antigens by two-dimensional gel electrophoresis. Several antigens, including the microneme protein MIC2, the cyst matrix protein MAG1, and the dense granule proteins GRA4 and GRA7, were commonly recognized by IgG antibodies from both groups of mice. There were multiple antigens recognized mostly by IgG antibodies of only one group of mice, either with or without cerebral tachyzoite growth. The antigens recognized only by or mostly by the antibodies of mice with cerebral tachyzoite growth include MIC6, the rhoptry protein ROP1, GRA2, one heat shock protein HSP90, one (putative) HSP70, and the myosin heavy chain. These results indicate that levels of IgG antibody to only selected T. gondii antigens increase in association with cerebral tachyzoite proliferation (reactivation of infection) in immunocompetent hosts with chronic infection.

Gene flow and biological conflict systems in the origin and evolution of eukaryotes

The endosymbiotic origin of eukaryotes brought together two disparate genomes in the cell. Additionally, eukaryotic natural history has included other endosymbiotic events, phagotrophic consumption of organisms, and intimate interactions with viruses and endoparasites. These phenomena facilitated large-scale lateral gene transfer and biological conflicts. We synthesize information from nearly two decades of genomics to illustrate how the interplay between lateral gene transfer and biological conflicts has impacted the emergence of new adaptations in eukaryotes. Using apicomplexans as example, we illustrate how lateral transfer from animals has contributed to unique parasite-host interfaces comprised of adhesion- and O-linked glycosylation-related domains. Adaptations, emerging due to intense selection for diversity in the molecular participants in organismal and genomic conflicts, being dispersed by lateral transfer, were subsequently exapted for eukaryote-specific innovations. We illustrate this using examples relating to eukaryotic chromatin, RNAi and RNA-processing systems, signaling pathways, apoptosis and immunity. We highlight the major contributions from catalytic domains of bacterial toxin systems to the origin of signaling enzymes (e.g., ADP-ribosylation and small molecule messenger synthesis), mutagenic enzymes for immune receptor diversification and RNA-processing. Similarly, we discuss contributions of bacterial antibiotic/siderophore synthesis systems and intra-genomic and intra-cellular selfish elements (e.g., restriction-modification, mobile elements and lysogenic phages) in the emergence of chromatin remodeling/modifying enzymes and RNA-based regulation. We develop the concept that biological conflict systems served as evolutionary “nurseries” for innovations in the protein world, which were delivered to eukaryotes via lateral gene flow to spur key evolutionary innovations all the way from nucleogenesis to lineage-specific adaptations.

Rhomboid proteases in plants - still in square one?

Rhomboids are ubiquitous intramembrane serine proteases the sequences of which are found in nearly all sequenced genomes, including those of plants. They were molecularly characterized in a number of organisms, and were found to play a role in a variety of biological functions including signaling, development, apoptosis, mitochondrial integrity, parasite invasion and more. Although rhomboid sequences are found in plants, very little is known about their function. Here, we present the current knowledge in the rhomboids field in general, and in plant rhomboids in particular. In addition, we discuss possible physiological roles of different plant rhomboids.