Protein export into malaria parasite-infected erythrocytes: mechanisms and functional consequences.

Phylum Apicomplexa comprises a large group of obligate intracellular parasites of high medical and veterinary importance. These organisms succeed intracellularly by effecting remarkable changes in a broad range of diverse host cells. The transformation of the host erythrocyte is particularly striking in the case of the malaria parasite Plasmodium falciparum. P. falciparum exports hundreds of proteins that mediate a complex cellular renovation marked by changes in the permeability, rigidity, and cytoadherence properties of the host erythrocyte. The past decade has seen enormous progress in understanding the identity and function of these exported effectors, as well as the mechanisms by which they are trafficked into the host cell. Here we review these advances, place them in the context of host manipulation by related apicomplexans, and propose key directions for future research.

The Crk4-Cyc4 complex regulates G2/M transition in Toxoplasma gondii.

A versatile division of apicomplexan parasites and a dearth of conserved regulators have hindered the progress of apicomplexan cell cycle studies. While most apicomplexans divide in a multinuclear fashion, Toxoplasma gondii tachyzoites divide in the traditional binary mode. We previously identified five Toxoplasma CDK-related kinases (Crk). Here, we investigated TgCrk4 and its cyclin partner TgCyc4. We demonstrated that TgCrk4 regulates conventional G2 phase processes, such as repression of chromosome rereplication and centrosome reduplication, and acts upstream of the spindle assembly checkpoint. The spatial TgCyc4 dynamics supported the TgCrk4-TgCyc4 complex role in the coordination of chromosome and centrosome cycles. We also identified a dominant TgCrk4-TgCyc4 complex interactor, TgiRD1 protein, related to DNA replication licensing factor CDT1 but played no role in licensing DNA replication in the G1 phase. Our results showed that TgiRD1 also plays a role in controlling chromosome and centrosome reduplication. Global phosphoproteome analyses identified TgCrk4 substrates, including TgORC4, TgCdc20, TgGCP2, and TgPP2ACA. Importantly, the phylogenetic and structural studies suggest the Crk4-Cyc4 complex is limited to a minor group of the binary dividing apicomplexans.

How Apicomplexa Parasites Secrete and Build Their Invasion Machinery.

Apicomplexa are obligatory intracellular parasites that sense and actively invade host cells. Invasion is a conserved process that relies on the timely and spatially controlled exocytosis of unique specialized secretory organelles termed micronemes and rhoptries. Microneme exocytosis starts first and likely controls the intricate mechanism of rhoptry secretion. To assemble the invasion machinery, micronemal proteins-associated with the surface of the parasite-interact and form complexes with rhoptry proteins, which in turn are targeted into the host cell. This review covers the molecular advances regarding microneme and rhoptry exocytosis and focuses on how the proteins discharged from these two compartments work in synergy to drive a successful invasion event. Particular emphasis is given to the structure and molecular components of the rhoptry secretion apparatus, and to the current conceptual framework of rhoptry exocytosis that may constitute an unconventional eukaryotic secretory machinery closely related to the one described in ciliates.

Comparative chemical genomics in Babesia species identifies the alkaline phosphatase PhoD as a determinant of antiparasitic resistance.

Babesiosis is an emerging zoonosis and widely distributed veterinary infection caused by 100+ species of Babesia parasites. The diversity of Babesia parasites and the lack of specific drugs necessitate the discovery of broadly effective antibabesials. Here, we describe a comparative chemogenomics (CCG) pipeline for the identification of conserved targets. CCG relies on parallel in vitro evolution of resistance in independent populations of Babesia spp. (B. bovis and B. divergens). We identified a potent antibabesial, MMV019266, from the Malaria Box, and selected for resistance in two species of Babesia. After sequencing of multiple independently derived lines in the two species, we identified mutations in a membrane-bound metallodependent phosphatase (phoD). In both species, the mutations were found in the phoD-like phosphatase domain. Using reverse genetics, we validated that mutations in bdphoD confer resistance to MMV019266 in B. divergens. We have also demonstrated that BdPhoD localizes to the endomembrane system and partially with the apicoplast. Finally, conditional knockdown and constitutive overexpression of BdPhoD alter the sensitivity to MMV019266 in the parasite. Overexpression of BdPhoD results in increased sensitivity to the compound, while knockdown increases resistance, suggesting BdPhoD is a pro-susceptibility factor. Together, we have generated a robust pipeline for identification of resistance loci and identified BdPhoD as a resistance mechanism in Babesia species.

Genetic crosses within and between species of Cryptosporidium.

Parasites and their hosts are engaged in reciprocal coevolution that balances competing mechanisms of virulence, resistance, and evasion. This often leads to host specificity, but genomic reassortment between different strains can enable parasites to jump host barriers and conquer new niches. In the apicomplexan parasite Cryptosporidium, genetic exchange has been hypothesized to play a prominent role in adaptation to humans. The sexual lifecycle of the parasite provides a potential mechanism for such exchange; however, the boundaries of Cryptosporidium sex are currently undefined. To explore this experimentally, we established a model for genetic crosses. Drug resistance was engineered using a mutated phenylalanyl tRNA synthetase gene and marking strains with this and the previously used Neo transgene enabled selection of recombinant progeny. This is highly efficient, and genomic recombination is evident and can be continuously monitored in real time by drug resistance, flow cytometry, and PCR mapping. Using this approach, multiple loci can now be modified with ease. We demonstrate that essential genes can be ablated by crossing a Cre recombinase driver strain with floxed strains. We further find that genetic crosses are also feasible between species. Crossing Cryptosporidium parvum, a parasite of cattle and humans, and Cryptosporidium tyzzeri a mouse parasite resulted in progeny with a recombinant genome derived from both species that continues to vigorously replicate sexually. These experiments have important fundamental and translational implications for the evolution of Cryptosporidium and open the door to reverse- and forward-genetic analysis of parasite biology and host specificity.

An apical membrane complex for triggering rhoptry exocytosis and invasion in Toxoplasma.

Apicomplexan parasites possess secretory organelles called rhoptries that undergo regulated exocytosis upon contact with the host. This process is essential for the parasitic lifestyle of these pathogens and relies on an exocytic machinery sharing structural features and molecular components with free-living ciliates. However, how the parasites coordinate exocytosis with host interaction is unknown. Here, we performed a Tetrahymena-based transcriptomic screen to uncover novel exocytic factors in Ciliata and conserved in Apicomplexa. We identified membrane-bound proteins, named CRMPs, forming part of a large complex essential for rhoptry secretion and invasion in Toxoplasma. Using cutting-edge imaging tools, including expansion microscopy and cryo-electron tomography, we show that, unlike previously described rhoptry exocytic factors, TgCRMPs are not required for the assembly of the rhoptry secretion machinery and only transiently associate with the exocytic site-prior to the invasion. CRMPs and their partners contain putative host cell-binding domains, and CRMPa shares similarities with GPCR proteins. Collectively our data imply that the CRMP complex acts as a host-molecular sensor to ensure that rhoptry exocytosis occurs when the parasite contacts the host cell.

Whole-genome CRISPR screens to understand Apicomplexan-host interactions.

Apicomplexan parasites are aetiological agents of numerous diseases in humans and livestock. Functional genomics studies in these parasites enable the identification of biological mechanisms and protein functions that can be targeted for therapeutic intervention. Recent improvements in forward genetics and whole-genome screens utilising CRISPR/Cas technology have revolutionised the functional analysis of genes during Apicomplexan infection of host cells. Here, we highlight key discoveries from CRISPR/Cas9 screens in Apicomplexa or their infected host cells and discuss remaining challenges to maximise this technology that may help answer fundamental questions about parasite-host interactions.

The cortical microtubules of Toxoplasma gondii underlie the helicity of parasite movement.

Motility is essential for apicomplexan parasites to infect their hosts. In a three-dimensional (3D) environment, the apicomplexan parasite Toxoplasma gondii moves along a helical path. The cortical microtubules, which are ultra-stable and spirally arranged, have been considered to be a structure that guides the long-distance movement of the parasite. Here, we address the role of the cortical microtubules in parasite motility, invasion and egress by utilizing a previously generated mutant (dubbed 'TKO') in which these microtubules are destabilized in mature parasites. We found that the cortical microtubules in ∼80% of the non-dividing (i.e. daughter-free) TKO parasites are much shorter than normal. The extent of depolymerization was further exacerbated upon commencement of daughter formation or cold treatment, but parasite replication was not affected. In a 3D Matrigel matrix, the TKO mutant moved directionally over long distances, but along trajectories that were significantly more linear (i.e. less helical) than those of wild-type parasites. Interestingly, this change in trajectory did not impact either movement speed in the matrix or the speed and behavior of the parasite during entry into and egress from the host cell.

Conservation, abundance, glycosylation profile, and localization of the TSP protein family in Cryptosporidium parvum.

Cryptosporidium parvum is a zoonotic apicomplexan parasite and a common cause of diarrheal disease worldwide. The development of vaccines to prevent or limit infection remains an important goal for tackling cryptosporidiosis. At present, the only approved vaccine against any apicomplexan parasite targets a conserved adhesin possessing a thrombospondin repeat domain. C. parvum possesses 12 orthologous thrombospondin repeat domain-containing proteins known as CpTSP1-12, though little is known about these potentially important antigens. Here, we explore the architecture and conservation of the CpTSP protein family, as well as their abundance at the protein level within the sporozoite stage of the life cycle. We examine the glycosylation states of these proteins using a combination of glycopeptide enrichment techniques to demonstrate that these proteins are modified with C-, O-, and N-linked glycans. Using expansion microscopy, and an antibody against the C-linked mannose that is unique to the CpTSP protein family within C. parvum, we show that these proteins are found both on the cell surface and in structures that resemble the secretory pathway of C. parvum sporozoites. Finally, we generated a polyclonal antibody against CpTSP1 to show that it is found at the cell surface and within micronemes, in a pattern reminiscent of other apicomplexan motility-associated adhesins, and is present both in sporozoites and meronts. This work sheds new light on an understudied family of C. parvum proteins that are likely to be important to both parasite biology and the development of vaccines against cryptosporidiosis.

Meat-Borne-Parasite: A Nanopore-Based Meta-Barcoding Work-Flow for Parasitic Microbiodiversity Assessment in the Wild Fauna of French Guiana.

French Guiana, located in the Guiana Shield, is a natural reservoir for many zoonotic pathogens that are of considerable medical or veterinary importance. Until now, there has been limited data available on the description of parasites circulating in this area, especially on protozoan belonging to the phylum Apicomplexa; conversely, the neighbouring countries describe a high parasitic prevalence in animals and humans. Epidemiological surveillance is necessary, as new potentially virulent strains may emerge from these forest ecosystems, such as Amazonian toxoplasmosis. However, there is no standard tool for detecting protozoa in wildlife. In this study, we developed Meat-Borne-Parasite, a high-throughput meta-barcoding workflow for detecting Apicomplexa based on the Oxford Nanopore Technologies sequencing platform using the 18S gene of 14 Apicomplexa positive samples collected in French Guiana. Sequencing reads were then analysed with MetONTIIME pipeline. Thanks to a scoring rule, we were able to classify 10 samples out of 14 as Apicomplexa positive and reveal the presence of co-carriages. The same samples were also sequenced with the Illumina platform for validation purposes. For samples identified as Apicomplexa positive by both platforms, a strong positive correlation at up to the genus level was reported. Overall, the presented workflow represents a reliable method for Apicomplexa detection, which may pave the way for more comprehensive biomonitoring of zoonotic pathogens.

Cimicifugin, a broad-spectrum inhibitor of Theileria annulata and Plasmodium falciparum CDK7.

Cyclin-dependent kinase 7 is an attractive therapeutic target for the treatment of cancers, and a previous report suggested that Plasmodium falciparum CDK7 is a potential drug target for developing new anti-malarial drugs. In this study, we aimed to characterize and evaluate the drug target potential of Theileria annulata CDK7. Theileria annulata is responsible for tropical theileriosis, which induces a phenotype similar to cancerous cells like immortalization, hyperproliferation, and dissemination. Virtual screening of the MyriaScreen II library predicted 14 compounds with high binding energies to the ATP-binding pocket of TaCDK7. Three compounds (cimicifugin, ST092793, and ST026925) of these 14 compounds were non-cytotoxic to the uninfected bovine cells (BoMac cells). Cimicifugin treatment led to the activation of the extrinsic apoptosis pathway and induced autophagy in T. annulata-infected cells. Furthermore, cimicifugin also inhibited the growth of P. falciparum, indicating that it has both anti-theilerial and anti-malarial activities and that TaCDK7 and PfCDK7 are promising drug targets.

Phylogenomics reveals Adeleorina are an ancient and distinct subgroup of Apicomplexa.

Apicomplexans are a diverse phylum of unicellular eukaryotes that share obligate relationships with terrestrial and aquatic animal hosts. Many well-studied apicomplexans are responsible for several deadly zoonotic and human diseases, most notably malaria caused by Plasmodium. Interest in the evolutionary origin of apicomplexans has also spurred recent work on other more deeply-branching lineages, especially gregarines and sister groups like squirmids and chrompodellids. But a full picture of apicomplexan evolution is still lacking several lineages, and one major, diverse lineage that is notably absent is the adeleorinids. Adeleorina apicomplexans comprises hundreds of described species that infect invertebrate and vertebrate hosts across the globe. Although historically considered coccidians, phylogenetic trees based on limited data have shown conflicting branch positions for this subgroup, leaving this question unresolved. Phylogenomic trees and large-scale analyses comparing cellular functions and metabolism between major subgroups of apicomplexans have not incorporated Adeleorina because only a handful of molecular markers and a couple organellar genomes are available, ultimately excluding this group from contributing to our understanding of apicomplexan evolution and biology. To address this gap, we have generated complete genomes from mitochondria and plastids, as well as multiple deep-coverage single-cell transcriptomes of nuclear genes from two Adeleorina species, Klossia helicina and Legerella nova, and inferred a 206-protein phylogenomic tree of Apicomplexa. We observed distinct structures reported in species descriptions as remnant host structures surrounding adeleorinid oocysts. Klossia helicina and L. nova branched, as expected, with monoxenous adeleorinids within the Adeleorina and their mitochondrial and plastid genomes exhibited similarity to published organellar adeleorinid genomes. We show with a phylogeneomic tree and subsequent phylogenomic analyses that Adeleorina are not closely related to any of the currently sampled apicomplexan subgroups, and instead fall as a sister to a large clade encompassing Coccidia, Protococcidia, Hematozoa, and Nephromycida, collectively. This resolves Adeleorina as a key independently-branching group, separate from coccidians, on the tree of Apicomplexa, which now has all known major lineages sampled.

Signaling Cascades Governing Entry into and Exit from Host Cells by Toxoplasma gondii.

The Apicomplexa phylum includes a large group of obligate intracellular protozoan parasites responsible for important diseases in humans and animals. Toxoplasma gondii is a widespread parasite with considerable versatility, and it is capable of infecting virtually any warm-blooded animal, including humans. This outstanding success can be attributed at least in part to an efficient and continuous sensing of the environment, with a ready-to-adapt strategy. This review updates the current understanding of the signals governing the lytic cycle of T. gondii, with particular focus on egress from infected cells, a key step for balancing survival, multiplication, and spreading in the host. We cover the recent advances in the conceptual framework of regulation of microneme exocytosis that ensures egress, motility, and invasion. Particular emphasis is given to the trigger molecules and signaling cascades regulating exit from host cells.

Let it glow: genetically encoded fluorescent reporters in Plasmodium.

The use of fluorescent proteins (FPs) in Plasmodium parasites has been key to understand the biology of this obligate intracellular protozoon. FPs like the green fluorescent protein (GFP) enabled to explore protein localization, promoter activity as well as dynamic processes like protein export and endocytosis. Furthermore, FP biosensors have provided detailed information on physiological parameters at the subcellular level, and fluorescent reporter lines greatly extended the malariology toolbox. Still, in order to achieve optimal results, it is crucial to know exactly the properties of the FP of choice and the genetic scenario in which it will be used. This review highlights advantages and disadvantages of available landing sites and promoters that have been successfully applied for the ectopic expression of FPs in Plasmodium berghei and Plasmodium falciparum. Furthermore, the properties of newly developed FPs beyond DsRed and EGFP, in the visualization of cells and cellular structures as well as in the sensing of small molecules are discussed.

Genome evolution in intracellular parasites: Microsporidia and Apicomplexa.

Microsporidia and Apicomplexa are eukaryotic, single-celled, intracellular parasites with huge public health and economic importance. Typically, these parasites are studied separately, emphasizing their uniqueness and diversity. In this review, we explore the huge amount of genomic data that has recently become available for the two groups. We compare and contrast their genome evolution and discuss how their transitions to intracellular life may have shaped it. In particular, we explore genome reduction and compaction, genome expansion and ploidy, gene shuffling and rearrangements, and the evolution of centromeres and telomeres.

Eimeria falciformis extracellular vesicles differentially express host cell lncRNAs.

Long noncoding RNAs (lncRNAs) are regulatory transcripts during protozoan infections in the host intestinal epithelial cells (IECs). Apicomplexan Eimeria falciformis sporozoite extracellular vesicles (EVs) contain virulence factors that modulate host IECs pro-inflammatory genes and immune responses. In this study, E. falciformis sporozoites were made to interact with inactivated host cells, and the parasite EVs were separated from total secretome by ultracentrifugation and purified on density gradient medium. Dose-dependent bio-activity of E. falciformis EVs was investigated by RNA sequencing, functional annotation and quantitative PCR. It was found that E. falciformis EVs induced mRNA, circRNA, and lncRNA expressions in mouse IECs. Of 38, 217 lncRNAs assembled, 157 and 152 were upwardly and downwardly expressed respectively. Differentially expressed lncRNAs were associated with cytokines, pyroptosis, and immune signaling pathways including FoxO, NF-κB, MAPK, and TGF-ß. In essence, E. falciformis EVs altered host cell RNA expressions during the interaction with host IECs. Also, differentially expressed lncRNAs are potential diagnostic transcripts during Eimeria infections.

Novel cytoskeletal traits in the intestinal parasites (Squirmida, Platyproteum vivax) of Pacific peanut worms (Sipuncula, Phascolosoma agassizii).

The cytoskeletal organization of a squirmid, namely Platyproteum vivax, was investigated with confocal laser scanning microscopy (CLSM) to refine inferences about convergent evolution among intestinal parasites of marine invertebrates. Platyproteum inhabits Pacific peanut worms (Phascolosoma agassizii) and has traits that are similar to other lineages of myzozoan parasites, namely gregarine apicomplexans within Selenidium, such as conspicuous feeding stages, called "trophozoites," capable of dynamic undulations. SEM and CLSM of P. vivax revealed an inconspicuous flagellar apparatus and a uniform array of longitudinal microtubules organized in bundles (LMBs). Extreme flattening of the trophozoites and a consistently oblique morphology of the anterior end provided a reliable way to distinguish dorsal and ventral surfaces. CLSM revealed a novel system of microtubules oriented in the flattened dorsoventral plane. Most of these dorsoventral microtubule bundles (DVMBs) had a punctate distribution and were evenly spaced along a curved line spanning the longitudinal axis of the trophozoites. This configuration of microtubules is inferred to function in maintaining the flattened shape of the trophozoites and facilitate dynamic undulations. The novel traits in Platyproteum are consistent with phylogenomic data showing that this lineage is only distantly related to Selenidium and other marine gregarine apicomplexans with dynamic intestinal trophozoites.

Molecular detection of Sarcocystis sp. in a kept under human care black capuchin monkey (Sapajus nigritus., Goldfuss 1809) with necrotizing encephalitis.

A senile male black capuchin monkey (Sapajus nigritus) kept under human care in a Zoo was found dead after 2 weeks presenting signals of weight loss and hyporexia. Histopathological revealed a necrotizing encephalitis. Although it was not observed microscopically, Sarcocystis sp infection was detected in brain tissue from molecular assays. These infections have been rarely described in neotropical primates, particularly associated with tissue lesions.

Fostering innovation to solve the biomechanics of microbe-host interactions: Focus on the adhesive forces underlying Apicomplexa parasite biology.

The protozoa, Toxoplasma gondii and Plasmodium spp., are preeminent members of the Apicomplexa parasitic phylum in large part due to their public health and economic impact. Hence, they serve as model unicellular eukaryotes with which to explore the repertoire of molecular and cellular strategies that specific developmental morphotypes deploy to timely adjust to their host(s) in order to perpetuate. In particular, host tissue- and cell-invasive morphotypes termed zoites alternate extracellular and intracellular lifestyles, thereby sensing and reacting to a wealth of host-derived biomechanical cues over their partnership. In the recent years, biophysical tools especially related to real time force measurement have been introduced, teaching us how creative are these microbes to shape a unique motility system that powers fast gliding through a variety of extracellular matrices, across cellular barriers, in vascular systems or into host cells. Equally performant was this toolkit to start illuminating how parasites manipulate their hosting cell adhesive and rheological properties to their advantage. In this review, besides highlighting major discoveries along the way, we discuss the most promising development, synergy, and multimodal integration in active noninvasive force microscopy methods. These should in the near future unlock current limitations and allow capturing, from molecules to tissues, the many biomechanical and biophysical interplays over the dynamic host and microbe partnership.

Correlations between the degree of infection by wild strain of Toxoplasma gondii in vitro and porcine hematological parameters.

The apicomplexa Toxoplasma gondii is capable of actively proliferating in numerous types of nucleated cells, and therefore has a high potential for dissemination and resistance. Thus, the present work aimed to correlate the inoculum concentrations and amount of post-infection parasites with porcine hematological parameters (including biochemistry) through in vitro culture. Porcine blood was incubated with different concentrations of parasites (1.2 × 107, 6/3/1.5 × 106 cells/mL), then the concentrations of red blood cells (RBC) and their morphology, total and differential leukocytes, and free peptides were evaluated. In addition, eight different blood samples analyzed before inoculation, where subsequent multivariate analysis was applied to correlate different variables with trophozoite concentration. The results showed no significant variation (p < 0.05) in the relative levels of free peptides, or the relative percentage of RBC at all the parasite concentrations tested. However, the normalized percentages of leukocytes and neutrophils showed a significant reduction, while those of lymphocytes, eosinophils and monocytes showed the opposite behavior. Semi-automatic processing of images exhibited significant microcytosis and hypochromia. The multivariate analysis revealed a positive correlation between the amount number of protozoa (AP) and the variables: "Red cells" and "Neutrophils", an indifference between the AP and the content of free peptides, and the concentration of monocytes in the samples; and a negative correlation for AP and the percentages of lymphocytes and eosinophils. Our results suggest that specific changes in hematological parameters may be associated with different degrees of parasitemia, demanding a thorough diagnostic process and adequate treatment.