Identification of three novel Toxoplasma gondii rhoptry proteins

The anticancer mechanisms of Toxoplasma gondii rhoptry protein 16 on lung adenocarcinoma cells

Lung adenocarcinoma is the most prevalent subtype of lung cancer, which is the leading cause of cancer-related mortality worldwide. Toxoplasma gondii (T.gondii) Rhoptry protein 16 (ROP16) has been shown to quickly enter the nucleus, and through activate host cell signaling pathways by phosphorylation STAT3 and may affect the survival of tumor cells. This study constructed recombinant lentiviral expression vector of T. gondii ROP16 I/II/III and stably transfected them into A549 cells, and the effects of ROP16 on cell proliferation, cell cycle, apoptosis, invasion, and migration of A549 cells were explored by utilizing CCK-8, flow cytometry, qPCR, Western blotting, TUNEL, Transwell assay, and cell scratch assay, and these effects were confirmed in the primary human lung adenocarcinoma cells from postoperative cancer tissues of patients. The type I and III ROP16 activate STAT3 and inhibited A549 cell proliferation, regulated the expression of p21, CDK6, CyclinD1, and induced cell cycle arrest at the G1 phase. ROP16 also regulated the Bax, Bcl-2, p53, cleaved-Caspase3, and Caspase9, inducing cell apoptosis, and reduced the invasion and migration of A549 cells, while type II ROP16 protein had no such effect. Furthermore, in the regulation of ROP16 on primary lung adenocarcinoma cells, type I and III ROP16 showed the same anticancer potential. These findings confirmed the anti-lung adenocarcinoma effect of type I and III ROP16, offering fresh perspectives on the possible application of ROP16 as a target with adjuvant therapy for lung adenocarcinoma and propelling the field of precision therapy research toward parasite treatment of tumors.

Cell cycle-regulated transcription factor AP2XII-9 is a key activator for asexual division and apicoplast inheritance in Toxoplasma gondii tachyzoite

Toxoplasma gondii is an intracellular parasitic protozoan that poses a significant risk to the fetus carried by a pregnant woman or to immunocompromised individuals. T. gondii tachyzoites duplicate rapidly in host cells during acute infection through endodyogeny. This highly regulated division process is accompanied by complex gene regulation networks. TgAP2XII-9 is a cell cycle-regulated transcription factor, but its specific role in the parasite cell cycle is not fully understood. In this study, we demonstrate that TgAP2XII-9 is identified as a nuclear transcription factor and is dominantly expressed during the S/M phase of the tachyzoite cell cycle. Cleavage Under Targets and Tagmentation (CUT&Tag) results indicate that TgAP2XII-9 targets key genes for the moving junction machinery (RON2, 4, and 8) and daughter cell inner membrane complex (IMC). TgAP2XII-9 deficiency resulted in a significant downregulation of rhoptry proteins and rhoptry neck proteins, leading to a severe defect in the invasion and egress efficiency of tachyzoites. Additionally, the loss of TgAP2XII-9 correlated with a substantial downregulation of multiple IMC and apicoplast proteins, leading to disorders of daughter bud formation and apicoplast inheritance and further contributing to the inability of cell division and intracellular proliferation. Our study reveals that TgAP2XII-9 acts as a critical S/M-phase regulator that orchestrates the endodyogeny and apicoplast division in T. gondii tachyzoites. This study contributes to a broader understanding of the complexity of the parasite's cell cycle and its key regulators.

IMPORTANCE

The intracellular apicoplast parasite Toxoplasma gondii poses a great threat to the public health. The acute infection of T. gondii tachyzoites relies on efficient invasion by forming a moving junction structure and also fast replication by highly regulated endodyogeny. This study shows that an ApiAP2 transcription factor, TgAP2XII-9, acts as an activator for the S/M-phase gene expression, including genes related to daughter buds and moving junction formation. Loss of TgAP2XII-9 results in significant growth defects and disorders in endodyogeny and apicoplast inheritance of the parasites. Our results provide valuable insights into the transcriptional regulation of the parasite cell cycle and invading machinery in T. gondii.

Genome-wide identification and molecular evolution of elongation family of very long chain fatty acids proteins in Cyrtotrachelus buqueti

To reveal the molecular function of elongation family of very long chain fatty acids(ELO) protein in Cyrtotrachelus buqueti, we have identified 15 ELO proteins from C.buqueti genome. 15 CbuELO proteins were located on four chromosomes. Their isoelectric points ranged from 9.22 to 9.68, and they were alkaline. These CbuELO proteins were stable and hydrophobic. CbuELO proteins had transmembrane movement, and had multiple phosphorylation sites. The secondary structure of CbuELO proteins was mainly α-helix. A total of 10 conserved motifs were identified in CbuELO protein family. Phylogenetic analysis showed that molecular evolutionary relationships of ELO protein family between C. buqueti and Tribolium castaneum was the closest. Developmental transcriptome analysis indicated that CbuELO10, CbuELO13 and CbuELO02 genes were key enzyme genes that determine the synthesis of very long chain fatty acids in pupae and eggs, CbuELO6 and CbuELO7 were that in the male, and CbuELO8 and CbuELO11 were that in the larva. Transcriptome analysis under different temperature conditions indicated that CbuELO1, CbuELO5, CbuELO12 and CbuELO14 participated in regulating temperature stress responses. Transcriptome analysis at different feeding times showed CbuELO12 gene expression level in all feeding time periods was significant downregulation. The qRT-PCR experiment verified expression level changes of CbuELO gene family under different temperature and feeding time conditions. Protein-protein interaction analysis showed that 9 CbuELO proteins were related to each other, CbuELO1, CbuELO4 and CbuELO12 had more than one interaction relationship. These results lay a theoretical foundation for further studying its molecular function during growth and development of C. buqueti.

TaqMan-quantitative PCR assays applied in Neospora caninum knock-outs generated through CRISPR-Cas9 allow to determine the copy numbers of integrated dihydrofolate reductase-thymidylate synthase drug selectable markers

As for many other organisms, CRISPR-Cas9 mediated genetic modification has gained increasing importance for the identification of vaccine candidates and drug targets in Neospora caninum, an apicomplexan parasite causing abortion in cattle and neuromuscular disease in dogs. A widely used approach for generating knock-out (KO) strains devoid of virulence factors is the integration of a drug selectable marker such as mutated dihydrofolate reductase-thymidylate synthase (mdhfr-ts) into the target gene, thus preventing the synthesis of respective protein and mediating resistance to pyrimethamine. However, CRISPR-Cas9 mutagenesis is not free of off-target effects, which can lead to integration of multiple mdhfr-ts copies into other sites of the genome. To determine the number of integrated mdhfr-ts in N. caninum, a duplex quantitative TaqMan PCR was developed. For this purpose, primers were designed that amplifies a 106 bp fragment from wild-type (WT) parasites corresponding to the single copy wtdhfrs-ts gene, as well as the mutated mdhfrs-ts present in KO parasites that confers resistance and were used simultaneously with primers amplifying the diagnostic NC5 gene. Thus, the dhfr-ts to NC5 ratio should be approximately 1 in WT parasites, while in KO parasites with a single integrated mdhrf-ts gene this ratio is doubled, and in case of multiple integration events even higher. This approach was applied to the Neospora KO strains NcΔGRA7 and NcΔROP40. For NcΔGRA7, the number of tachyzoites determined by dhfr-ts quantification was twice the number of tachyzoites determined by NC5 quantification, thus indicating that only one mdhfr-ts copy was integrated. The results obtained with the NcΔROP40 strain, however, showed that the number of dhfr-ts copies per genome was substantially higher, indicating that at least three copies of the selectable mdhfr-ts marker were integrated into the genomic DNA during gene editing by CRISPR-Cas9. This duplex TaqMan-qPCR provides a reliable and easy-to-use tool for assessing CRISPR-Cas9 mediated mutagenesis in WT N. caninum strains.

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Bioinformatics-based prediction and screening of immunogenic epitopes of Toxoplasma gondii rhoptry proteins 7, 21 and 22 as candidate vaccine target

Introduction

Toxoplasmosis is a well-known zoonotic disease caused by Toxoplasma gondii. The main causes of the disease range from eating undercooked or contaminated meat and shellfish to cleaning litter trays into which cats that excreted toxoplasma via faeces. This pathogen can live for a very long time, possibly a lifetime, within the bodies of humans and other animals.

Aims and objectives

This study aimed to predict and analyse candidate immunogenic epitopes for vaccine development by evaluating the physio-chemical properties, multiple sequence alignment, secondary and tertiary structures, phosphorylation sites, transmembrane domains, and signal peptides, of T. gondii rhoptry proteins ROP7, ROP21, and ROP22 using bioinformatics tools.

Methods

To find immunogenic epitopes of rhoptry proteins, numerous bioinformatics web servers were used containing multiple sequence alignment, physiochemical properties, antigenicity and allergenicity, post-translational modification sites (PTMs), signal peptides, transmembrane domains, secondary and tertiary structures, and screening of predicted epitopes. We evaluated immunogenic linear B-cell epitopes as candidate proteins for vaccine development.

Results

Nine epitopes were identified for each protein, and analysis of immunogenicity, revealed three candidate epitopes for ROP7, one for ROP21, and four for ROP22. Among all candidate epitopes, ROP22 contained the most immunogenic epitopes with immunogenicity score of 0.50575.

Conclusion

We acquired detailed information on predicted immunogenic epitopes using in-silico methods. The results provide a foundation for further experimental analysis of toxoplasmosis, and potential vaccine development.

Unifying Virulence Evaluation in Toxoplasma gondii: A Timely Task

Toxoplasma gondii, a major zoonotic pathogen, possess a significant genetic and phenotypic diversity that have been proposed to be responsible for the variation in clinical outcomes, mainly related to reproductive failure and ocular and neurological signs. Different T. gondii haplogroups showed strong phenotypic differences in laboratory mouse infections, which provide a suitable model for mimicking acute and chronic infections. In addition, it has been observed that degrees of virulence might be related to the physiological status of the host and its genetic background. Currently, mortality rate (lethality) in outbred laboratory mice is the most significant phenotypic marker, which has been well defined for the three archetypal clonal types (I, II and III) of T. gondii; nevertheless, such a trait seems to be insufficient to discriminate between different degrees of virulence of field isolates. Many other non-lethal parameters, observed both in in vivo and in vitro experimental models, have been suggested as highly informative, yielding promising discriminatory power. Although intra-genotype variations have been observed in phenotypic characteristics, there is no clear picture of the phenotypes circulating worldwide; therefore, a global overview of T. gondii strain mortality in mice is presented here. Molecular characterization has been normalized to some extent, but this is not the case for the phenotypic characterization and definition of virulence. The present paper proposes a baseline (minimum required information) for the phenotypic characterization of T. gondii virulence and intends to highlight the needs for consistent methods when a panel of T. gondii isolates is evaluated for virulence.

Evolutionary Analysis of Dipeptidyl Peptidase I

Human dipeptidyl peptidase I (DPPI) belongs to the family of papain-like cysteine peptidases. Its distinctive features are the unique exclusion domain which enables the eponymous activity and homotetramerization of DPPI, and its dependence on chloride ions for enzymatic activity. The oligomeric state of DPPI is unique in this family of predominantly monomeric peptidases. However, a distant DPPI ortholog from Plasmodium falciparum has been shown to be monomeric, indicating that the oligomeric state of DPPI varies between lineages. The aim of this work was to study the evolution of DPPI, with particular attention to the structural features that determine its characteristic enzymatic activity and preferences, and to reconstruct the evolution of its oligomerization. We analyzed fifty-seven selected sequences of DPPI and confirmed its presence in three lineages, namely, Amorphea (including animals and Amoebozoa), Alveolates and the metamonad Giardia. The amino acid residues that bind the chloride ion are highly conserved in all species, indicating that the dependence on chloride ions for activity is an evolutionarily conserved feature of DPPI. The number of N-glycosylation sites is significantly increased in animals, particularly vertebrates. Analysis of homology models and subunit contacts suggests that oligomerization is likely restricted to DPPIs in the Amorphea group.

Genome-Wide Expression Patterns of Rhoptry Kinases during the Eimeria tenella Life-Cycle

Kinome from apicomplexan parasites is composed of eukaryotic protein kinases and Apicomplexa specific kinases, such as rhoptry kinases (ROPK). Ropk is a gene family that is known to play important roles in host–pathogen interaction in Toxoplasma gondii but is still poorly described in Eimeria tenella, the parasite responsible for avian coccidiosis worldwide. In the E. tenella genome, 28 ropk genes are predicted and could be classified as active (n = 7), inactive (incomplete catalytic triad, n = 12), and non-canonical kinases (active kinase with a modified catalytic triad, n = 9). We characterized the ropk gene expression patterns by real-time quantitative RT-PCR, normalized by parasite housekeeping genes, during the E. tenella life-cycle. Analyzed stages were: non-sporulated oocysts, sporulated oocysts, extracellular and intracellular sporozoites, immature and mature schizonts I, first- and second-generation merozoites, and gametes. Transcription of all those predicted ropk was confirmed. The mean intensity of transcription was higher in extracellular stages and 7–9 ropk were specifically transcribed in merozoites in comparison with sporozoites. Transcriptional profiles of intracellular stages were closely related to each other, suggesting a probable common role of ROPKs in hijacking signaling pathways and immune responses in infected cells. These results provide a solid basis for future functional analysis of ROPK from E. tenella.

Designing and developing of high-resolution melting technique for separating different types of Toxoplasma gondii by analysis of B1 and ROP8 gene regions

BACKGROUND

Determination of Toxoplasma gondii genotypes plays an important role in the health management and epidemiology of toxoplasmosis. We developed HRM analysis to differentiate genotypes of T. gondii using the B1 and ROP8 genes, through comparing the sensitivity and specificity of both genes and methods used for the detection of T. gondii.

METHODS

A total of 96 DNA samples of muscle tissue of livestock and poultry brain tissue with three standard strains RH (type I), PRU (type II) and VEG (type III) were prepared and analyzed. Three methods of nested PCR, PCR-PCR and nested-qPCR-HRM were used. Specific new primers were designed and synthesized for developing HRM. Thirty positive samples obtained from nested-qPCR-HRM were sequenced (18 B1 and 12 ROP8).

RESULTS

Overall, 87 infected samples were identified using both genes. Through the B1 gene, we could separate type I (T_m = 84.8 °C) from II/III types (T_m = 84.6 °C). Also, the ROP8 gene could separate type II (T_m = 84.5 °C) from I/III types (T_m = 84.12 °C). Highest sensitivity (100%) and specificity (78.72%) were observed by nested-qPCR-HRM assays of the B1 and ROP8 genes than by other methods, respectively. Thus, the B1 gene can be used to most accurately detect T. gondii, while the ROP8 gene was more appropriate for T. gondii genotyping. PCR-sequencing results were consistent with HRM results in most selected samples.

CONCLUSION

HRM analysis is a powerful diagnostic tool for rapid detection and determination of main clonal lineages, and even unusual T. gondii genotypes.

Naïve CD8 T cell IFNγ responses to a vacuolar antigen are regulated by an inflammasome-independent NLRP3 pathway and Toxoplasma gondii ROP5

Host resistance to Toxoplasma gondii relies on CD8 T cell IFNγ responses, which if modulated by the host or parasite could influence chronic infection and parasite transmission between hosts. Since host-parasite interactions that govern this response are not fully elucidated, we investigated requirements for eliciting naïve CD8 T cell IFNγ responses to a vacuolar resident antigen of T. gondii, TGD057. Naïve TGD057 antigen-specific CD8 T cells (T57) were isolated from transnuclear mice and responded to parasite-infected bone marrow-derived macrophages (BMDMs) in an antigen-dependent manner, first by producing IL-2 and then IFNγ. T57 IFNγ responses to TGD057 were independent of the parasite’s protein export machinery ASP5 and MYR1. Instead, host immunity pathways downstream of the regulatory Immunity-Related GTPases (IRG), including partial dependence on Guanylate-Binding Proteins, are required. Multiple T. gondii ROP5 isoforms and allele types, including ‘avirulent’ ROP5A from clade A and D parasite strains, were able to suppress CD8 T cell IFNγ responses to parasite-infected BMDMs. Phenotypic variance between clades B, C, D, F, and A strains suggest T57 IFNγ differentiation occurs independently of parasite virulence or any known IRG-ROP5 interaction. Consistent with this, removal of ROP5 is not enough to elicit maximal CD8 T cell IFNγ production to parasite-infected cells. Instead, macrophage expression of the pathogen sensors, NLRP3 and to a large extent NLRP1, were absolute requirements. Other members of the conventional inflammasome cascade are only partially required, as revealed by decreased but not abrogated T57 IFNγ responses to parasite-infected ASC, caspase-1/11, and gasdermin D deficient cells. Moreover, IFNγ production was only partially reduced in the absence of IL-12, IL-18 or IL-1R signaling. In summary, T. gondii effectors and host machinery that modulate parasitophorous vacuolar membranes, as well as NLR-dependent but inflammasome-independent pathways, determine the full commitment of CD8 T cells IFNγ responses to a vacuolar antigen.

Parasites are excellent “students” of our immune system as they can deflect, antagonize and confuse the immune response making it difficult to vaccinate against these pathogens. In this report, we analyzed how a widespread parasite of mammals, Toxoplasma gondii, manipulates an immune cell needed for immunity to many intracellular pathogens, the CD8 T cell. Host pathways that govern CD8 T cell production of the immune protective cytokine, IFNγ, were also explored. We hypothesized the secreted T. gondii virulence factor, ROP5, work to inhibit the MHC 1 antigen presentation pathway therefore making it difficult for CD8 T cells to see T. gondii antigens sequestered inside a parasitophorous vacuole. However, manipulation through T. gondii ROP5 does not fully explain how CD8 T cells commit to making IFNγ in response to infection. Importantly, CD8 T cell IFNγ responses to T. gondii require the pathogen sensor NLRP3 to be expressed in the infected cell. Other proteins associated with NLRP3 activation, including members of the conventional inflammasome activation cascade pathway, are only partially involved. Our results identify a novel pathway by which NLRP3 regulates T cell function and underscore the need for NLRP3-activating adjuvants in vaccines aimed at inducing CD8 T cell IFNγ responses to parasites.

Toxoplasma gondii Recombinant Antigens in the Serodiagnosis of Toxoplasmosis in Domestic and Farm Animals

Simple Summary

The very common parasite infections in animals are caused by members of Apicomplexa, including Toxoplasma gondii, Neospora sp., and Sarcocystis sp. These parasites pose serious veterinary problems. For example, the development of unambiguous diagnostic algorithms and determining the correct diagnosis are hindered by the similar antigenic structure of these parasites, as well as the multitude of similar disease symptoms presented in an infected animal. The intracellular parasite, T. gondii, infects a wide range of warm-blooded animals, including humans. This parasite is widespread among different animal populations, contributes to the loss of reproductive and malformations in young individuals, and can become a serious economic concern for farmers. Additionally, the consumption of undercooked or raw meat and the consumption of improperly processed milk product derived from farm animals are the main parasite transmission routes in humans. This work reviews potential improvements to diagnostic techniques that use recombinant antigens for serodiagnosis of toxoplasmosis in various species of animals.

Abstract

Toxoplasmosis is caused by an intracellular protozoan, Toxoplasma gondii, and is a parasitic disease that occurs in all warm-blooded animals, including humans. Toxoplasmosis is one of the most common parasitic diseases of animals and results in reproductive losses. Toxoplasmosis in humans is usually caused by eating raw or undercooked meat or consuming dairy products containing the parasite. Diagnosis of toxoplasmosis is currently based on serological assays using native antigens to detect specific anti-T. gondii antibodies. Due to the high price, the available commercial agglutination assays are not suited to test a large number of animal serum samples. The recent development of proteomics elucidated the antigenic structure of T. gondii and enabled the development of various recombinant antigens that can be used in new, cheaper, and more effective diagnostic tools. Continuous development of scientific disciplines, such as molecular biology and genetic engineering, allows for the production of new recombinant antigens and provides the basis for new diagnostic tests for the detection of anti-T. gondii antibodies in animal serum samples.

Loss of rhoptry protein 9 impeded Toxoplasma gondii infectivity

Toxoplasma gondii is an obligatory intracellular parasite that critically depends on active invasion and egress from infected host cells to complete its propagation cycle. T. gondii rhoptry proteins (TgROPs) are virulent factors associated with host cell invasion, growth. In this study, we analyzed the functions of ROP9 in the process of T. gondii infection. The TgROP9 knockout RH strain (RH△ROP9) and its recovery strain (RH-ReROP9) were constructed using the CRISPR/Cas9 system. The invasion, proliferation, and egress efficiency of the RH△ROP9 strain were evaluated and their pathogenicity to mice was analyzed. Compared with RH wild-type (RH-WT) and RH-ReROP9 strains, the invasion percentage of RH△ROP9 to Vero cells was reduced by about 28.0% (p< 0.01) at 1.5 h, and the relative proliferation percentage was decreased by about 35.0% (p< 0.01) after infection with 10² or 10³ parasites. In addition, the RH△ROP9 strain also showed prolonged egress time from host cells. The survival time of the mice (12.6 ± 1.6 or 10.1 ± 1.1 days) were delayed (p < 0.001) after infection with either 200 or 1000 RH△ROP9 parasites. These evidences suggested that ROP9 facilitated T. gondii infection in vitro and in vivo.

A single-parasite transcriptional atlas of Toxoplasma Gondii reveals novel control of antigen expression

Toxoplasma gondii, a protozoan parasite, undergoes a complex and poorly understood developmental process that is critical for establishing a chronic infection in its intermediate hosts. Here, we applied single-cell RNA-sequencing (scRNA-seq) on >5,400 Toxoplasma in both tachyzoite and bradyzoite stages using three widely studied strains to construct a comprehensive atlas of cell-cycle and asexual development, revealing hidden states and transcriptional factors associated with each developmental stage. Analysis of SAG1-related sequence (SRS) antigenic repertoire reveals a highly heterogeneous, sporadic expression pattern unexplained by measurement noise, cell cycle, or asexual development. Furthermore, we identified AP2IX-1 as a transcription factor that controls the switching from the ubiquitous SAG1 to rare surface antigens not previously observed in tachyzoites. In addition, comparative analysis between Toxoplasma and Plasmodium scRNA-seq results reveals concerted expression of gene sets, despite fundamental differences in cell division. Lastly, we built an interactive data-browser for visualization of our atlas resource.

In Vivo CRISPR Screen Identifies TgWIP as a Toxoplasma Modulator of Dendritic Cell Migration

Toxoplasma can reach distant organs, especially the brain, leading to a lifelong chronic phase. However, genes involved in related in vivo processes are currently unknown. Here, we use focused CRISPR libraries to identify Toxoplasma genes that affect in vivo fitness. We focus on TgWIP, whose deletion affects Toxoplasma dissemination to distant organs. We show that TgWIP is secreted into the host cell upon invasion and interacts with the host WAVE regulatory complex and SHP2 phosphatase, both of which regulate actin dynamics. TgWIP affects the morphology of dendritic cells and mediates the dissolution of podosomes, which dendritic cells use to adhere to extracellular matrix. TgWIP enhances the motility and transmigration of parasitized dendritic cells, likely explaining its effect on in vivo fitness. Our results provide a framework for systemic identification of Toxoplasma genes with in vivo effects at the site of infection or on dissemination to distant organs, including the brain.

Automated Spatially Targeted Optical Microproteomics (autoSTOMP) to Determine Protein Complexity of Subcellular Structures

Spatially targeted optical microproteomics (STOMP) is a method to study region-specific protein complexity in primary cells and tissue samples. STOMP uses a confocal microscope to visualize structures of interest and to tag the proteins within those structures by a photodriven cross-linking reaction so that they can be affinity purified and identified by mass spectrometry (eLife 2015, 4, e09579). However, the use of a custom photo-cross-linker and the requirement for extensive user intervention during sample tagging have posed barriers to the utilization of STOMP. To address these limitations, we built automated STOMP (autoSTOMP) which uses a customizable code in SikuliX to coordinate image capture and cross-linking functions in Zeiss Zen Black with image processing in FIJI. To increase protocol accessibility, we implemented a commercially available biotin-benzophenone photo-cross-linking and purification protocol. Here we demonstrate that autoSTOMP can efficiently label, purify, and identify proteins belonging to 1-2 μm structures in primary human foreskin fibroblasts or mouse bone marrow-derived dendritic cells infected with the protozoan parasite Toxoplasma gondii (Tg). AutoSTOMP can easily be adapted to address a range of research questions using Zeiss Zen Black microscopy systems and LC-MS protocols that are standard in many research cores.

Rhoptry antigens as Toxoplasma gondii vaccine target

Toxoplasmosis is a cosmopolitan zoonotic infection, caused by a unicellular protozoan parasite known as Toxoplasma gondii that belongs to the phylum Apicomplexa. It is estimated that over one-third of the world's population has been exposed and are latently infected with the parasite. In humans, toxoplasmosis is predominantly asymptomatic in immunocompetent persons, while among immunocompromised individuals may be cause severe and progressive complications with poor prognosis. Moreover, seronegative pregnant mothers are other risk groups for acquiring the infection. The life cycle of T. gondii is very complex, indicating the presence of a plurality of antigenic epitopes. Despite of great advances, recognize and construct novel vaccines for prevent and control of toxoplasmosis in both humans and animals is still remains a great challenge for researchers to select potential protein sequences as the ideal antigens. Notably, in several past years, constant efforts of researchers have made considerable advances to elucidate the different aspects of the cell and molecular biology of T. gondii mainly on microneme antigens, dense granule antigens, surface antigens, and rhoptry proteins (ROP). These attempts thereby provided great impetus to the present focus on vaccine development, according to the defined subcellular components of the parasite. Although, currently there is no commercial vaccine for use in humans. Among the main identified T. gondii antigens, ROPs appear as a putative vaccine candidate that are vital for invasion procedure as well as survival within host cells. Overall, it is estimated that they occupy about 1%–30% of the total parasite cell volume. In this review, we have summarized the recent progress of ROP-based vaccine development through various strategies from DNA vaccines, epitope or multi epitope-based vaccines, recombinant protein vaccines to vaccines based on live-attenuated vectors and prime-boost strategies in different mouse models.

An in silico pipeline to filter the Toxoplasma gondii proteome for proteins that could traffic to the host cell nucleus and influence host cell epigenetic regulation

Toxoplasma gondii uses epigenetic mechanisms to regulate both endogenous and host cell gene expression. To identify genes with putative epigenetic functions, we developed an in silico pipeline to interrogate the T. gondii proteome of 8313 proteins. Step 1 employs PredictNLS and NucPred to identify genes predicted to target eukaryotic nuclei. Step 2 uses GOLink to identify proteins of epigenetic function based on Gene Ontology terms. This resulted in 611 putative nuclear localised proteins with predicted epigenetic functions. Step 3 filtered for secretory proteins using SignalP, SecretomeP, and experimental data. This identified 57 of the 611 putative epigenetic proteins as likely to be secreted. The pipeline is freely available online, uses open access tools and software with user-friendly Perl scripts to automate and manage the results, and is readily adaptable to undertake any such in silico search for genes contributing to particular functions.

Identification of Antigenic and Immunogenic Proteins of Toxoplasma gondii in Human and Sheep by Immunoproteomics

BACKGROUND

Toxoplasmosis is a parasitic disease caused by the intracellular protozoan parasite, Toxoplasma gondii, which can infect humans and warm-blooded animals. This infection can lead to still birth and abortion among some susceptible hosts especially sheep and human in pregnancy. Development of a vaccine against T. gondii infection is very important-especially for use in immunocompromised patients, pregnant women, and sheep. Different antigens of T. gondii can be potential candidates for immunization. The aims of this study were to identify the immunodominant and antigenic proteins of T. gondii in sheep and man.

METHODS

Tachyzoites' proteins were separated by two-dimensional polyacrylamide gel electrophoresis (2-DE), and subjected to western blot analysis probed with T. gondii positive sera of sheep and human (Biotechnology Department of Pasteur Institute of Tehran, Iran, from April 2016 to March 2017). Finally, the immunoreactive proteins were identified by mass spectrometry (MALDI-TOF/MS and MS/MS) technique.

RESULTS

Five immunoreactive and antigenic proteins were recognized by Toxoplasma positive sera of human and sheep. These identified proteins were Enolase 2, rhoptry protein 4 (ROP4), dense granular protein 14 (GRA14), rhoptry protein 15 (ROP15) and rhoptry protein 9 (ROP9).

CONCLUSION

The identified immunodominant proteins have potential to be used as diagnostic antigens and as diagnostic markers of Toxoplasma infection in sheep and human.

Functional Characterization of Rhoptry Kinome in the Virulent Toxoplasma gondii RH Strain

Toxoplasma gondii is an obligatory intracellular apicomplexan protozoan which can infect any warm-blooded animal and causes severe diseases in immunocompromised individuals or infants infected in utero. The survival and success of this parasite require that it colonizes the host cell, avoids host immune defenses, replicates within an appropriate niche, and exits the infected host cell to spread to neighboring non-infected cells. All of these processes depend on the parasite ability to synthesis and export secreted proteins. Amongst the secreted proteins, rhoptry organelle proteins (ROPs) are essential for the parasite invasion and host cell manipulation. Even though the functions of most ROPs have been elucidated in the less virulent T. gondii (type II), the roles of ROPs in the highly virulent type I strain remain largely un-characterized. Herein, we investigated the contributions of 15 ROPs (ROP10, ROP11, ROP15, ROP20, ROP23, ROP31, ROP32, ROP33, ROP34, ROP35, ROP36, ROP40, ROP41, ROP46, and ROP47) to the infectivity of the high virulent type I T. gondii (RH strain). Using CRISPR-Cas9, these 15 ROPs genes were successfully disrupted and the effects of gene knockout on the parasite's ability to infect cells in vitro and BALB/c mice in vivo were investigated. These results showed that deletions of these ROPs did not interfere with the parasite ability to grow in cultured human foreskin fibroblast cells and did not significantly alter parasite pathogenicity for BALB/c mice. Although these ROPs did not seem to be essential for the acute infectious stage of type I T. gondii in the mouse model, they might have different functions in other intermediate hosts or play different roles in other life cycle forms of this parasite due to the different expression patterns; this warrants further investigations.

The Past, Present, and Future of Genetic Manipulation in Toxoplasma gondii

Toxoplasma gondii is a classic model for studying obligate intracellular microorganisms as various genetic manipulation tools have been developed in T. gondii over the past 20 years. Here we summarize the major strategies for T. gondii genetic manipulation including genetic crosses, insertional mutagenesis, chemical mutagenesis, homologous gene replacement, conditional knockdown techniques, and the recently developed clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system. We evaluate the advantages and limitations of each of these tools in a historical perspective. We also discuss additional applications of modified CRISPR-Cas9 systems for use in T. gondii, such as regulation of gene expression, labeling of specific genomic loci, and epigenetic modifications. These approaches have the potential to revolutionize the analysis of T. gondii biology and help us to better develop new drugs and vaccines.

The Toxoplasma gondii Rhoptry Kinome Is Essential for Chronic Infection

Ingestion of the obligate intracellular protozoan parasite Toxoplasma gondii causes an acute infection that leads to chronic infection of the host. To facilitate the acute phase of the infection, T. gondii manipulates the host response by secreting rhoptry organelle proteins (ROPs) into host cells during its invasion. A few key ROP proteins with signatures of kinases or pseudokinases (ROPKs) act as virulence factors that enhance parasite survival against host gamma interferon-stimulated innate immunity. However, the roles of these and other ROPK proteins in establishing chronic infection have not been tested. Here, we deleted 26 ROPK gene loci encoding 31 unique ROPK proteins of type II T. gondii and show that numerous ROPK proteins influence the development of chronic infection. Cyst burdens were increased in the Δrop16 knockout strain or moderately reduced in 11 ROPK knockout strains. In contrast, deletion of ROP5, ROP17, ROP18, ROP35, or ROP38/29/19 (ROP38, ROP29, and ROP19) severely reduced cyst burdens. Δrop5 and Δrop18 knockout strains were less resistant to host immunity-related GTPases (IRGs) and exhibited >100-fold-reduced virulence. ROP18 kinase activity and association with the parasitophorous vacuole membrane were necessary for resistance to host IRGs. The Δrop17 strain exhibited a >12-fold defect in virulence; however, virulence was not affected in the Δrop35 or Δrop38/29/19 strain. Resistance to host IRGs was not affected in the Δrop17, Δrop35, or Δrop38/29/19 strain. Collectively, these findings provide the first definitive evidence that the type II T. gondii ROPK proteome functions as virulence factors and facilitates additional mechanisms of host manipulation that are essential for chronic infection and transmission of T. gondii.

Reactivation of chronic Toxoplasma gondii infection in individuals with weakened immune systems causes severe toxoplasmosis. Existing treatments for toxoplasmosis are complicated by adverse reactions to chemotherapy. Understanding key parasite molecules required for chronic infection provides new insights into potential mechanisms that can interrupt parasite survival or persistence in the host. This study reveals that key secreted rhoptry molecules are used by the parasite to establish chronic infection of the host. Certain rhoptry proteins were found to be critical virulence factors that resist innate immunity, while other rhoptry proteins were found to influence chronic infection without affecting virulence. This study reveals that rhoptry proteins utilize multiple mechanisms of host manipulation to establish chronic infection of the host. Targeted disruption of parasite rhoptry proteins involved in these biological processes opens new avenues to interfere with chronic infection with the goal to either eliminate chronic infection or to prevent recrudescent infections.

Bioinformatics analysis and expression of a novel protein ROP48 in Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular apicomplexan parasite, and can infect warmblooded animals and humans all over the world. In the past years, ROP family genes encoding particular proteins of T. gondii had made a great contribution to toxoplasmosis. In this study, we used multiple bioinformatics approaches to predict the physical and chemical characteristics, transmembrane domain, epitope, and topological structure of the rhoptry protein 48 (ROP48). The results indicated that ROP48 protein was mainly located in the membrane and had several positive linear-B cell epitopes and Th-cell epitopes, which suggested that ROP48 is a potential DNA vaccine candidate against toxoplasmosis. Then the PCR product amplified from the ROP48 cDNA was inserted into a pEASY-T1 vector to build a recombinant cloning plasmid. After sequencing, ROP48 was subcloned into a eukaryotic expression plasmid pEGFP-C1 to obtain pEGFP-C1-ROP48 (pROP48). After identification by PCR and restriction enzyme digestion, the recombinant plasmid pROP48 was transfected into HEK 293-T cell and identified by RT-PCR. The results showed that the eukaryotic expression plasmid pROP48 was constructed and transfected to the cells of HEK 293-T successfully. Western blotting showed that the expressed proteins can be recognized by anti-STAg mouse sera.

Rhoptry protein 47 gene sequence: A potential novel genetic marker for population genetic studies of Toxoplasma gondii

Toxoplasma gondii, an obligate intracellular parasite, is able to infect many animal species and humans, and can cause toxoplasmosis of the host. In this study, we examined sequence variation in rhoptry protein 47 (ROP47) gene among T. gondii isolates originating from different hosts and geographical regions. The entire genome region of the ROP47 gene was amplified and sequenced, and phylogenetic relationship was reconstructed using maximum parsimony (MP), maximum likelihood (ML) and neighbor-joining (NJ), based on the ROP47 gene sequences. The results of sequence alignments showed that all ROP47 gene sequences were 396 bp in length. There were 19 variable nucleotide positions in the coding region, resulted in 16 amino acid substitutions (12.21%) among all examined T. gondii strains and the existence of polymorphic restriction sites for endonucleases SacI and AflIII, allowing the differentiation of the three major clonal lineage types I, II and III by PCR-RFLP. Phylogenetic analysis of ROP47 gene sequences showed that three major clonal lineage types I, II and III were clustered differently, consistent with PCR-RFLP results. These results suggest that ROP47 gene sequence may represent a potential novel genetic marker for population genetic studies of T. gondii isolates.

Identifying novel cell cycle proteins in Apicomplexa parasites through co-expression decision analysis

Hypothetical proteins comprise roughly half of the predicted gene complement of Toxoplasma gondii and Plasmodium falciparum and represent the largest class of uniquely functioning proteins in these parasites. Following the idea that functional relationships can be informed by the timing of gene expression, we devised a strategy to identify the core set of apicomplexan cell division cycling genes with important roles in parasite division, which includes many uncharacterized proteins. We assembled an expanded list of orthologs from the T. gondii and P. falciparum genome sequences (2781 putative orthologs), compared their mRNA profiles during synchronous replication, and sorted the resulting set of dual cell cycle regulated orthologs (744 total) into protein pairs conserved across many eukaryotic families versus those unique to the Apicomplexa. The analysis identified more than 100 ortholog gene pairs with unknown function in T. gondii and P. falciparum that displayed co-conserved mRNA abundance, dynamics of cyclical expression and similar peak timing that spanned the complete division cycle in each parasite. The unknown cyclical mRNAs encoded a diverse set of proteins with a wide range of mass and showed a remarkable conservation in the internal organization of ordered versus disordered structural domains. A representative sample of cyclical unknown genes (16 total) was epitope tagged in T. gondii tachyzoites yielding the discovery of new protein constituents of the parasite inner membrane complex, key mitotic structures and invasion organelles. These results demonstrate the utility of using gene expression timing and dynamic profile to identify proteins with unique roles in Apicomplexa biology.