Biology subjects

Coppens, I.

Publications and source records attributed to Coppens, I..

At least 19 recordsLinked to original sources

bioRxiv2026

The live attenuated DGAT1-knockout whole-cell Toxoplasma vaccine confers protective immunity against acute and chronic toxoplasmosis

The intravacuolar parasite Toxoplasma gondii scavenges fatty acids from host mammalian cells and stores excess in lipid droplets. To investigate the physiological relevance of neutral lipid storage in Toxoplasma, we generated a mutant lacking DGAT1, an ER-localized enzyme that synthesizes triacylglycerols, from the virulent type I RH strain of T. gondii. Compared to WT, RH {Delta}DGAT1 parasites grow poorly in mammalian cells, form few LD, suffer from lipotoxicity, and do not cause disease or lethality in immunocompetent or immunodeficient mice. Importantly, mice immunized with RH {Delta}DGAT1 parasites mount strong, long-term immune responses involving both cellular and humoral components, with higher levels of T. gondii-specific IgG antibodies, effector memory T cells, and both pro-inflammatory and anti-inflammatory cytokines, indicating a mixed Th1/Th2 response with Th1 predominance. This immunity provides complete, long-lasting protection (up to 6 months) against rechallenge from homologous type I (acute infection) and heterologous cyst-forming type II (chronic infection) T. gondii strains. Additional analyses reveal that IFN-{gamma}, CD8+ T cells, as well as B cells are crucial for defending against type I T. gondii in immunized mice. Overall, our live-attenuated RH {Delta}DGAT1 strain is a promising vaccine candidate and a model for studying immune responses that control T. gondii infections.

microbiology↗

bioRxiv2025

Acute induction of IFNα is responsible for the attenuation of the live measles vaccine

The live-attenuated measles vaccine (LAMV) protects against measles in a safe, efficacious and durable manner. However, the mechanism by which LAMV is attenuated is not well understood, contributing to the increased vaccine hesitancy that has caused a worldwide resurgence of measles. Here, we provide a molecular model of attenuation that implicates increased host innate immune responses and increased LAMV susceptibility to those responses. Our study leverages both in vitro and in vivo models of infection to find that acute induction of innate immunity in immune cells is the critical determinant of LAMV attenuation. We show that LAMV, in contrast to pathogenic wild type measles virus (MeV), causes a strong IFN response in primary human peripheral blood mononuclear cells, which restricts viral replication and spread in a post-entry manner. LAMV can enter, transcribe viral mRNA and translate viral proteins in immune cells, but is not able to form infectious particles and spread from cell to cell. Specifically, we find that mutations conserved across LAMV strains in the P/V/C and H genes are responsible for the induction of IFN and the restriction of infectious virus production. In PBMC cultures and in rhesus macaques, LAMV infection also results in the acute induction of proinflammatory cytokines that likely play a role in the immunogenicity of the vaccine. Overall, our study provides a virological and immunological framework for LAMV attenuation which can be leveraged in repurposing the LAMV backbone and in future vaccine design.

microbiology↗

bioRxiv2025

High-Resolution Proteomics Unveils Salivary Gland Disruption and Saliva-Hemolymph Protein Exchange in Plasmodium-Infected Mosquitoes

Plasmodium sporozoites, the stage that initiates a malaria infection, must invade the mosquito salivary glands (SGs) before transmitting to a vertebrate host. However, the effects of sporozoite invasion on salivary gland physiology and saliva composition remain largely unexplored. We examined the impact of Plasmodium infection on Anopheles gambiae salivary glands using high-resolution proteomics, gene expression, and morphological analysis. The data revealed differential expression of various proteins, including the enrichment of humoral proteins in infected salivary glands originating from the hemolymph. These proteins diffused into the SGs due to structural damage caused by the sporozoites during invasion. Conversely, saliva proteins diffused out into the circulation of infected mosquitoes. Moreover, infection altered saliva protein composition, as shown by proteomes from saliva collected from mosquitoes infected by P. berghei or P. falciparum, revealing a significant reduction of immune proteins compared to uninfected mosquitoes. This reduction is likely due to the association of these proteins with the surface of sporozoites within the mosquito salivary secretory cavities. The saliva protein profiles from mosquitoes infected with both Plasmodium species were remarkably similar, suggesting a conserved interaction between sporozoites and salivary glands. Our results provide a foundation for understanding the molecular interactions between Plasmodium sporozoites and mosquito salivary glands.

microbiology↗

bioRxiv2024

Calcium tunneling through the entoplasmic reticulum and transfer to other organelles for optimal signaling in Toxoplasma gondii

Ca2+ signaling in cells begins with the opening of Ca2+ channels in either the plasma membrane (PM) or endoplasmic reticulum (ER), leading to a sharp increase of the physiologically low (<100 nM) cytosolic Ca2+ level. The temporal and spatial regulation of Ca{superscript 2} is crucial for the precise activation of key biological processes. In the apicomplexan parasite Toxoplasma gondii, which infects approximately one-third of the global population, Ca{superscript 2} signaling governs essential aspects of the parasites infection cycle. T. gondii relies on Ca{superscript 2} signals to regulate pathogenic traits, with several Ca{superscript 2}-signaling components playing critical roles. Ca2+ entry from the extracellular environment has been demonstrated in T. gondii for both, extracellular parasites, exposed to high Ca2+, and intracellular parasites, which acquire Ca{superscript 2} from host cells during host Ca{superscript 2} signaling events. Active egress, an essential step of the parasites infection cycle, is preceded by a large increase in cytosolic Ca2+, most likely initiated by release from intracellular stores. However, extracellular Ca2+ is also necessary to reach a cytosolic Ca2+ threshold required for timely egress. In this study, we investigated the mechanism of Ca{superscript 2} intracellular store replenishment and identified a central role for the SERCA-Ca2+-ATPase in maintaining Ca{superscript 2} homeostasis not only within the ER but also in other organelles. We demonstrate mitochondrial Ca2+ uptake, which occurs by transfer of Ca2+ from the ER, likely through membrane contact sites. Our findings suggest that the T. gondii ER plays a key role in sequestering and redistributing Ca{superscript 2} to intracellular organelles following Ca{superscript 2} influx at the PM. HIGHLIGHTSThe T. gondii ER takes up Ca2+ that enters the cytosol from the extracellular milieu. Filling of acidic stores in T. gondii depends on ER Ca{superscript 2} content. The mitochondrion of T. gondii has no direct access to extracellular Ca{superscript 2} but can take it up via transfer from the ER and/or acidic stores. The absence of SERCA activity results in reduced Ca{superscript 2} levels in the ER as well as in other organelles

cell biology↗

bioRxiv2023

XIAP-mediated targeting of endolysosomes to stressed mitochondria occurs in a switch-like, global manner and results in autophagy-independent, sub-organelle level mitochondrial degradation

Damaged mitochondria can be subject to lysosomal degradation via mitophagy. However, whole-organelle degradation exhibits relatively slow kinetics and thus its impact may be limited in response to acute, fast-acting cellular stress. We previously reported that in Parkin-deficient cells endolysosomes directly target mitochondria when subjected to bioenergetic stress. Here, using high-resolution live cell imaging we reveal a striking level of dynamic targeting of Rab5+ early endosomes to stressed mitochondria, culminating in a switch-like accumulation in the entire mitochondrial population, independently of canonical autophagy. This process of rapid, largescale Rab5+ vesicle trafficking to mitochondria coincides with, and is mediated by, XIAP E3 ligase activated mitochondrial ubiquitylation and results in ultrastructural changes to, and degradation of, intra-mitochondrial components. Mitochondria-targeting vesicles include early endosomal subpopulations marked by Rab5 effector APPL1 and ubiquitin-binding endocytic adaptors OPTN, TAX1BP1 and Tollip, and Rab7-positive late endosomes/lysosomes. In Parkin expressing cells, XIAP- and Parkin-dependent mitochondrial targeting and resulting processing modes are competitively regulated. Together, our data suggest that XIAP-mediated targeting of endolysosomes to mitochondria functions as a stress-responsive, sub-organelle level mitochondrial processing mode that is distinct from, and competitive to, Parkin-mediated mitophagy.

cell biology↗

bioRxiv2023

Functional profiling of the Toxoplasma genome during acute mouse infection

Within a host, pathogens encounter a diverse and changing landscape of cell types, nutrients, and immune responses. Examining host-pathogen interactions in animal models can therefore reveal aspects of infection absent from cell culture. We use CRISPR-based screens to functionally profile the entire genome of the model apicomplexan parasite Toxoplasma gondii during mouse infection. Barcoded gRNAs were used to track mutant parasite lineages, enabling detection of bottlenecks and mapping of population structures. We uncovered over 300 genes that modulate parasite fitness in mice with previously unknown roles in infection. These candidates span multiple axes of host-parasite interaction, including determinants of tropism, host organelle remodeling, and metabolic rewiring. We mechanistically characterized three novel candidates, including GTP cyclohydrolase I, against which a small-molecule inhibitor could be repurposed as an antiparasitic compound. This compound exhibited antiparasitic activity against T. gondii and Plasmodium falciparum, the most lethal agent of malaria. Taken together, we present the first complete survey of an apicomplexan genome during infection of an animal host, and point to novel interfaces of host-parasite interaction that may offer new avenues for treatment.

microbiology↗

bioRxiv2023

In vitro production of cat-restricted Toxoplasma pre-sexual stages by epigenetic reprogramming

Summary paragraphSexual reproduction of Toxoplasma gondii, which is restricted to the small intestine of felids, is sparsely documented, due to ethical concerns surrounding the use of cats as model organisms. Chromatin modifiers dictate the developmental fate of the parasite during its multistage life cycle, but their targeting to stage-specific cistromes is poorly described1. In this study, we found that transcription factors AP2XII-1 and AP2XI-2, expressed in tachyzoite stage that causes acute toxoplasmosis, can silence genes necessary for merozoites, a developmental stage critical for sexual commitment and transmission to the next host, including humans. Their conditional and simultaneous depletion leads to a drastic change in the transcriptional program, promoting a complete transition from tachyzoites to merozoites. Pre-gametes produced in vitro under these conditions are characterized by specific protein markers and undergo typical asexual endopolygenic division cycles. In tachyzoites, AP2XII-1 and AP2XI-2 bind DNA as heterodimers at merozoite promoters and recruit the epigenitors MORC and HDAC31, which in turn restrict the accessibility of chromatin to the transcriptional machinery. Thus, the commitment to merogony stems from a profound epigenetic rewiring orchestrated by AP2XII-1 and AP2XI-2. This effective in vitro culture of merozoites paves the way to explore Toxoplasma sexual reproduction without the need to infect kittens and has potential for the development of therapeutics to block parasite transmission.

microbiology↗

bioRxiv2022

Host MOSPD2 enrichment at the parasitophorous vacuole membrane varies between Toxoplasma strains and involves complex interactions

Toxoplasma gondii is an obligate, intracellular parasite capable of causing severe disease in warm-blooded animals. Infection of a cell produces a unique niche for the parasite named the parasitophorous vacuole (PV) initially composed of host plasma membrane invaginated during invasion. The PV and its membrane (PVM) are subsequently decorated with a variety of parasite proteins allowing the parasite to optimally grow in addition to manipulate host processes. Recently, we reported a proximity-labeling screen at the PVM-host interface and identified host ER-resident MOSPD2 as being enriched at this location. Here we extend these findings in several important respects. First, we show that the extent and pattern of host MOSPD2 association with the PVM differs dramatically in cells infected with different strains of Toxoplasma. Second, in cells infected with Type I RH strain, the MOSPD2 staining is mutually exclusive with regions of the PVM that associate with mitochondria. Third, immunoprecipitation and LC-MS/MS with epitope-tagged MOSPD2-expressing host cells reveals strong enrichment of several PVM-localized parasite proteins, although none appear to play an essential role in MOSPD2 association. Lastly, most MOSPD2 associating with the PVM is newly translated after infection of the cell and requires the major functional domains of MOSPD2, identified as the CRAL/TRIO domain and tail anchor, although these domains were not sufficient for PVM association. Collectively, these studies provide new insight into the molecular interactions involving MOSPD2 at the dynamic interface between the PVM and the host cytosol. ImportanceToxoplasma gondii is an intracellular pathogen that lives within a membranous vacuole inside of its host cell. This vacuole is decorated by a variety of parasite proteins that allow it to defend against host attack, acquire nutrients, and interact with the host cell. Recent work identified and validated host proteins enriched at this host-pathogen interface. Here, we follow up on one candidate named MOSPD2 shown to be enriched at the vacuolar membrane and describe it as having a dynamic interaction at this location depending on a variety of factors. Some of these include the presence of host mitochondria, intrinsic domains of the host protein, and whether translation is active. Importantly, we show that MOSPD2 enrichment at the vacuole membrane differs between strains indicating active involvement of the parasite with this phenotype. Altogether, these results shed light on the mechanism and role of protein associations in the host-pathogen interaction.

microbiology↗

bioRxiv2022

Toxoplasma scavenges mammalian host organelles through usurpation of host ESCRT-III and Vps4

Intracellular pathogens exploit cellular resources through host cell manipulation. Within its nonfusogenic parasitophorous vacuole (PV), Toxoplasma targets host nutrient-filled organelles and sequesters them into the PV through deep invaginations of the PV membrane (PVM) that ultimately detach from this membrane. Some of these invaginations are generated by an intravacuolar network (IVN) of parasite-derived tubules fusing with the PVM. Here, we examine the parasite usurpation of host ESCRT-III and Vps4 to create PVM buds and vesicles. CHMP4B associates with the PVM/IVN and dominant negative (DN) CHMP4B forms many long PVM invaginations containing CHMP4B filaments; the invaginations are shorter in IVN-deficient parasites, suggesting cooperation between IVN and ESCRT. In infected cells expressing Vps4-DN, enlarged intra-PV structures containing host endo-lysosomes accumulate, reflecting defects in PVM scission. Parasite mutants lacking TgGRA14 or TgGRA64 that interact with ESCRT have reduced CHMP4B-DN-induced PVM invaginations and intra-PV host organelles, with greater defects in a double-knockout, revealing the exploitation of ESCRT to scavenge host organelles by Toxoplasma. SummaryThe parasite Toxoplasma sequesters host nutrient-filled organelles into its parasitophorous vacuole through its exploitation of host ESCRT-III and Vps4 for vacuolar membrane-remodeling and fission processes utilizing the parasite proteins TgGRA14 and TgGRA64 that interact with ESCRT.

microbiology↗

bioRxiv2022

Toxoplasma gondii-s basal complex: the other apicomplexan business end is multifunctional

The Apicomplexa are famously named for their apical complex, a constellation of organelles at their apical end dedicated to invasion of their host cells. In contrast, at the other end of the cell, the basal complex (BC) has been in the limelight since it is much less prominent and specific functions were not immediately obvious. However, in the past decade a staggering array of functions have been associated with the BC, and strides have been made in understanding its structure. Here, these collective insights are supplemented with new data to provide an overview of the understanding of the BC in Toxoplasma gondii. The emerging picture is that the BC is a dynamic and multifunctional complex, with a series of (putative) functions. The BC has multiple roles in cell division: it is the site where building blocks are added to the cytoskeleton scaffold; it exerts a two-step stretch and constriction mechanism as contractile ring; and it is key in organelle division. Furthermore, the BC has numerous putative roles in import, such as the recycling of mother cell remnants, the acquisition of host-derived vesicles, possibly the uptake of lipids derived from the extracellular medium, and the endocytosis of micronemal proteins. The latter process ties the BC to motility, whereas an additional role in motility is conferred by Myosin C. Furthermore, the BC acts on the assembly and/or function of the intravacuolar network, which may directly or indirectly contribute to the establishment of chronic tissue cysts. Here we provide experimental support for molecules acting in several of these processes, and identify several new BC proteins critical to maintaining the cytoplasmic bridge between divided parasites. However, the dispensable nature of many BC components leaves many questions unanswered regarding its function. In conclusion, the BC in T. gondii is a dynamic and multifunctional structure at the posterior end of the parasite.

cell biology↗

bioRxiv2021

Dense granule protein, GRA64 interacts with host cell ESCRT proteins during Toxoplasma gondii infection

The intracellular parasite Toxoplasma gondii adapts to diverse host cell environments within a replicative compartment that is heavily decorated by secreted proteins. In attempts to identify novel parasite secreted proteins that influence host cell activity, we identified and characterized a trans-membrane dense granule protein dubbed GRA64 (TGME49_202620). We found that GRA64 is on the parasitophorous vacuolar membrane (PVM) and is partially exposed to the host cell cytoplasm in both tachyzoite and bradyzoite parasitophorous vacuoles. Using co-immunoprecipitation and proximity-based biotinylation approaches, we demonstrate that GRA64 appears to interact with certain components of the host Endosomal Sorting Complexes Required for Transport (ESCRT). Genetic disruption of GRA64 does not affect acute Toxoplasma virulence in mice nor encystation as observed via tissue cyst burdens in mice during chronic infection. However, ultrastructural analysis of {Delta}gra64 tissue cysts using electron tomography revealed enlarged vesicular structures underneath the cyst membrane, suggesting a role for GRA64 in organizing the recruitment of ESCRT proteins and subsequent intracystic vesicle formation. This study uncovers a novel host-parasite interaction that contributes to an emerging paradigm in which specific host ESCRT proteins are recruited to the limiting membranes (PVMs) of tachyzoite and bradyzoite vacuoles formed during acute and chronic Toxoplasma infection. IMPORTANCEToxoplasma gondii is a widespread foodborne parasite that causes congenital disease and life-threatening complications in immune compromised individuals. Part of this parasites success lies in its ability to infect diverse organisms and host cells, as well as to persist as a latent infection within parasite constructed structures called tissue cysts. In this study, we characterized a protein secreted by T. gondii into its parasitophorous vacuole during intracellular infection, which we dub GRA64. On the vacuole, this protein is exposed to the host cell and interacts with specific host ESCRT proteins. Parasites lacking the GRA64 protein exhibit ultrastructural changes in tissue cysts during chronic infection. This study lays the foundation for future studies on the mechanics and consequences of host ESCRT-parasite protein interactions.

microbiology↗

bioRxiv2021

The Rab11-Family Interacting Proteins reveal selective interaction of mammalian recycling endosomes with the Toxoplasma parasitophorous vacuole in a Rab11- and Arf6-dependent manner

After invasion of mammalian cells, the parasite Toxoplasma gondii multiplies in a self-made membrane-bound compartment, the parasitophorous vacuole (PV). We previously showed that intravacuolar Toxoplasma interacts with many host cell organelles, especially recycling endosomes, and further manipulates the host endocytic recycling through the sequestration of Rab11 vesicles into the PV. Mammalian Rab-PV interactions are likely mediated by Toxoplasma and host proteins that remain to be identified. In this context, we have examined the specificity of host Rab vesicle interaction with the PV by monitoring the recruitment of subtypes of Rab11 vesicles differing in their composition in Rab11-Family Interacting Proteins (FIPs). We found that vesicles with FIPs from Class I (FIP1C, FIP2, FIP5) or Class II (FIP3, FIP4) are distributed at the PV and detected to varying degrees inside the PV. The PV delivery of vesicles with FIPs from Class I, but not Class II, is Rab11-dependent. In addition to Rab11, FIP3 binds to Arf6, and vesicles associated with FIP3-Arf6 complexes are observed within the PV. Binding of FIP3 to either Rab11 or Arf6 significantly increases the internalization of vesicles into the PV. These data point to a selective process of host recycling endosome recognition and scavenging mediated by Toxoplasma.

cell biology↗

bioRxiv2020

Unusual Features of the Membrane Kinome of Trypanosoma brucei

In many eukaryotes, multiple protein kinases are situated in the plasma membrane where they respond to extracellular ligands. Ligand binding elicits a signal that is transmitted across the membrane, leading to activation of the cytosolic kinase domain. Humans have over 100 receptor protein kinases. In contrast, our search of the Trypanosoma brucei kinome showed that there were only ten protein kinases with predicted transmembrane domains, and unlike other eukaryotic transmembrane kinases, seven are predicted to bear multiple transmembrane domains. Most of the ten kinases, including their transmembrane domains, are conserved in both Trypanosoma cruzi and Leishmania species. Several possess accessory domains, such as Kelch, nucleotide cyclase, and forkhead-associated domains. Surprisingly, two contain multiple regions with predicted structural similarity to domains in bacterial signaling proteins. A few of the protein kinases have previously been localized to subcellular structures such as endosomes or lipid bodies. We examine here the localization of epitope-tagged versions of seven of the predicted transmembrane kinases in T. brucei bloodstream forms and show that five localized to the endoplasmic reticulum. The last two kinases are integral membrane proteins associated with the flagellum, flagellar pocket, or adjacent structures, as shown by both fluorescence and immunoelectron microscopy. Thus, these kinases are positioned in structures suggesting participation in signal transduction from the external environment.

molecular biology↗

bioRxiv2020

Chemoprophylaxis vaccination with a Plasmodium liver stage autophagy mutant affords enhanced and long-lasting protection

Genetically-attenuated sporozoite vaccines can elicit long-lasting protection against malaria but pose risks of breakthrough infection. Chemoprophylaxis vaccination (CVac) has proven to be the most effective vaccine strategy against malaria. Though CVac with WT sporozoites confers better immunity, the overhanging threat of drug resistance limits its use as a vaccine. Here, we demonstrate that a liver stage-specific mutant of Plasmodium berghei when used as a vaccine under a CVac regimen provides superior long-lasting protection, in both inbred and outbred mice, as compared to WT-CVac. Uniquely, the protection elicited by this mutant is predominantly dependent on a CD8+T-cell response through an IFN-{gamma}-independent mechanism and is associated with a stable population of antigen-experienced CD8+T cells. Jointly, our findings support the benefit of liver stage mutants as vaccines over WT, under a CVac protocol. This vaccination strategy is also a powerful model to study the mechanisms of protective immunity and discover new protective antigens.

immunology↗

bioRxiv2020

Toxoplasma TgATG9 is critical for autophagy and long-term persistence in tissue cysts

Many of the worlds warm-blooded species are chronically infected with Toxoplasma gondii tissue cysts, including up to an estimated one third of the global human population. The cellular processes that permit long-term parasite persistence within the cyst are largely unknown, not only for T. gondii but also for related coccidian parasites that impact human and animal health. A previous study revealed an accumulation of autophagic material in the lysosome-like Vacuolar Compartment (VAC) of chronic stage bradyzoites lacking functional cathepsin L protease (TgCPL) activity. Furthermore, it was shown that TgCPL knockout bradyzoites have compromised viability, indicating the turnover of autophagic material could be necessary for bradyzoite survival. However, the extent to which autophagy itself contributes to bradyzoite development and fitness remained unknown. Herein we show that genetic ablation of TgATG9 substantially reduces canonical autophagy and compromises bradyzoite viability. Transmission electron microscopy revealed structural abnormalities occurring in {Delta}atg9 bradyzoites, including disorganization of the inner membrane complex and plasma membrane, the occurrence of multiple nuclei within a single bradyzoite cell, as well as various anomalies associated with the VAC. TgATG9-deficient bradyzoites accumulated significantly less undigested material in the VAC upon inhibition of TgCPL activity, suggesting that autophagy contributes material to the VAC for degradation. Intriguingly, abnormal mitochondria networks were observed in TgATG9-deficient bradyzoites. They were thin and elongated and often adopted a horseshoe conformation. Some abnormal mitochondrial structures were found to contain numerous different cytoplasmic components and organelles. Bradyzoite fitness was found to be drastically compromised, both in vitro and in mice, with very few brain cysts identified in mice 5 weeks post-infection. Taken together, our data suggests that TgATG9, and by extension autophagy, is critical for cellular homeostasis in bradyzoites and is necessary for long-term persistence within the cyst of this coccidian parasite.

microbiology↗

bioRxiv2020

Toxoplasma ferlin1 is a versatile and dynamic mediator of microneme trafficking and secretion

Toxoplasma gondii is a polarized cell concentrating several secretory organelles at the apical pole. The secretory micronemes come in two sub-populations differentiated by dependence on the Rab5A/C in their biogenesis. Calcium-dependent exocytosis of micronemes occurs at the very apical tip and is critical for parasite egress from its host cell, adhesion and invasion of the next cell. Ferlins represent a protein family with roles in exocytosis containing multiple Ca2+-sensing C2 domains. We determined that T. gondiis ferlin 1 (FER1) localized dynamically to the parasites secretory pathway. FER1 function was dissected by dominant negative overexpression strategies. We demonstrated that FER1 traffics microneme organelles along the following trajectories:1. From the trans-Golgi-endosomes network to the subpellicular cortex; 2. Along the cortex to the apical end; 3. To the apical tip for fusion with the plasma membrane; 4. Retrograde transport allowing microneme recycling from mother to daughter; 5. Differential microneme sub-population traffic. Finally, FER1 overexpression triggers a microneme exocytosis burst, supporting the notion that the radially organized micronemes at the apical tip comprise a readily-releasable microneme pool. In summary, FER1 is pivotal for dynamic microneme trafficking, acts differently on the two microneme subpopulations, and acts on the plasma membrane fusion step during microneme exocytosis.

cell biology↗

bioRxiv2020

Fussing about fission: defining variety among mainstream and exotic apicomplexan cell division modes

Cellular reproduction defines life, yet our textbook-level understanding of cell division is limited to a small number of model organisms centered around humans. The horizon on cell division variants is expanded here by advancing insights on the fascinating cell division modes found in the Apicomplexa, a key group of protozoan parasites. The Apicomplexa display remarkable variation in offspring number, whether karyokinesis follows each S/M-phase or not, and whether daughter cells bud in the cytoplasm or bud from the cortex. We find that the terminology used to describe the various manifestations of asexual apicomplexan cell division emphasizes either the number of offspring or site of budding, which are not directly comparable features and has led to confusion in the literature. Division modes have been primarily studied in two human pathogenic Apicomplexa, malaria-causing Plasmodium spp. and Toxoplasma gondii, a major cause of opportunistic infections. Plasmodium spp. divide asexually by schizogony, producing multiple daughters per division round through a cortical budding process, though at several life-cycle nuclear amplifications are not followed by karyokinesis. T. gondii divides by endodyogeny producing two internally budding daughters per division round. Here we add to this diversity in replication mechanisms by considering the cattle parasite Babesia bigemina and the pig parasite Cystoisospora suis. B. bigemina produces two daughters per division round by a binary fission mechanism whereas C. suis produces daughters through both endodyogeny and multiple internal budding known as endopolygeny. In addition, we provide new data from the causative agent of equine protozoal myeloencephalitis (EPM), Sarcocystis neurona, which also undergoes endopolygeny but differs from C. suis by maintaining a single multiploid nucleus. Overall, we operationally define two principally different division modes: internal budding found in cyst-forming Coccidia (comprising endodyogeny and two forms of endopolygeny) and external budding found in the other parasites studied (comprising the two forms of schizogony, binary fission and multiple fission). Progressive insights into the principles defining the molecular and cellular requirements for internal versus external budding, as well as variations encountered in sexual stages are discussed. The evolutionary pressures and mechanisms underlying apicomplexan cell division diversification carries relevance across Eukaryota. Contribution to the FieldMechanisms of cell division vary dramatically across the Tree of Life, but the mechanistic basis has only been mapped for several model organisms. Here we present cell division strategies across Apicomplexa, a group of obligate intracellular parasites with significant impact on humans and domesticated animals. Asexual apicomplexan cell division is organized around assembly of daughter buds, but division forms differ in the cellular site of budding, number of offspring per division round, whether each S-phase follows karyokinesis and if mitotic rounds progress synchronously. This varies not just between parasites, but also between different life-cycle stages of a given species. We discuss the historical context of terminology describing division modes, which has led to confusion on how different modes relate to each other. Innovations in cell culture and genetics together with light microscopy advances have opened up cell biological studies that can shed light on this puzzle. We present new data for three division modes barely studied before. Together with existing data, we show how division modes are organized along phylogenetic lines and differentiate along external and internal budding mechanisms. We also discuss new insights into how the variations in division mode are regulated at the molecular level, and possess unique cell biological requirements.

microbiology↗

bioRxiv2019

A role for Toxoplasma gondii chloroquine resistance transporter in bradyzoite viability and digestive vacuole maintenance

Toxoplasma gondii is a ubiquitous pathogen that can cause encephalitis, congenital defects, and ocular disease. T. gondii has also been implicated as a risk factor for mental illness in humans. The parasite persists in the brain as slow growing bradyzoites contained within intracellular cysts. No treatments exist to eliminate this form of parasite. Although proteolytic degradation within the parasite lysosomal-like vacuolar compartment (VAC) is critical for bradyzoite viability, whether other aspects of the VAC are important for parasite persistence remains unknown. An ortholog of Plasmodium falciparum CRT has previously been identified in T. gondii (TgCRT). To interrogate the function of TgCRT in chronic stage bradyzoites and its role in persistence, we knocked out TgCRT in a cystogenic strain and assessed VAC size, VAC digestion of host-derived proteins and parasite autophagosomes, and viability of in vitro and in vivo bradyzoites. We found that whereas parasites deficient in TgCRT exhibit normal digestion within the VAC, they display a markedly distended VAC and their viability is compromised both in vitro and in vivo. Interestingly, impairing VAC proteolysis in TgCRT deficient bradyzoites restored VAC size, consistent with a role for TgCRT as a transporter of products of digestion from the VAC. In conjunction with earlier studies, our current findings suggest a functional link between TgCRT and VAC proteolysis. This work provides further evidence of a crucial role for the VAC in bradyzoite persistence and a new potential VAC target to abate chronic Toxoplasma infection.\n\nIMPORTANCEIndividuals chronically infected with the intracellular parasite Toxoplasma gondii are at risk of experiencing reactivated disease that can result in progressive loss of vision. No effective treatments exist for chronic toxoplasmosis due in part to a poor understanding of the biology underlying chronic infection and a lack of well validated potential targets. Here we show that a T. gondii transporter is functionally linked to protein digestion within the parasite lysosome-like organelle and that this transporter is necessary to sustain chronic infection in culture and in experimentally infected mice. Ablating the transporter results in severe bloating of the lysosome-like organelle. Together with earlier work, this study suggests the parasites lysosome-like organelle is vital for parasite survival, thus rendering it a potential target for diminishing infection and reducing the risk of reactivated disease.

microbiology↗