A Signaling Factor Linked to Toxoplasma gondii Guanylate Cyclase Complex Controls Invasion and Egress during Acute and Chronic Infection

First identified Toxoplasma gondii Type I in market-sold ducks in Fujian province, China: a significant for public health

Toxoplasma gondii (T. gondii) is an intracellular protozoan that can cause toxoplasmosis in all warm-blooded hosts. This study focused on the prevalence and genetic characterize of T. gondii in ducks from Fujian province, China. Genomic DNA was extracted from duck tissue samples (heart, liver, lung, and muscle). To assess the genetic diversity of the T. gondii isolates, it was determined by using multilocus polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technology. A total of 586 ducks from 5 cities in Fujian province were tested, and 35 (6.0%) of which were found to be positive for the T. gondii B1 gene. Further genotyping of these positive samples at 10 genetic markers (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico) using PCR-RFLP revealed that one tissue samples (heart samples from Fuzhou ducks) were identified as Type I (ToxoDB#10). This study is the first report on the prevalence and genetic characterization of T. gondii in ducks in Fujian province, and Type I (ToxoDB#10) is found in ducks in China for the first time. The findings document the genetic characterization of T. gondii in free-range ducks from Fujian Province, thereby enriching the understanding of T. gondii genetic diversity in China. Moreover, these results provide essential data support for further prospective studies and underscores the "One Health" concept, emphasizing the integral link among human, animal, and environmental health.

Functional analyses of Toxoplasma gondii dihydroorotase reveal a promising anti-parasitic target

Toxoplasma gondii relies heavily on the de novo pyrimidine biosynthesis pathway for fueling the high uridine-5'-monophosphate (UMP) demand during parasite growth. The third step of de novo pyrimidine biosynthesis is catalyzed by dihydroorotase (DHO), a metalloenzyme that catalyzes the reversible condensation of carbamoyl aspartate to dihydroorotate. Here, functional analyses of TgDHO reveal that tachyzoites lacking DHO are impaired in overall growth due to decreased levels of UMP, and the noticeably growth restriction could be partially rescued after supplementation with uracil or high concentrations of L-dihydroorotate in vitro. When pyrimidine salvage pathway is disrupted, both DHOH35A and DHOD284E mutant strains proliferated much slower than DHO-expressing parasites, suggesting an essential role of both TgDHO His35 and Asp284 residues in parasite growth. Additionally, DHO deletion causes the limitation of bradyzoite growth under the condition of uracil supplementation or uracil deprivation. During the infection in mice, the DHO-deficient parasites are avirulent, despite the generation of smaller tissue cysts. The results reveal that TgDHO contributes to parasite growth both in vitro and in vivo. The significantly differences between TgDHO and mammalian DHO reflect that DHO can be exploited to produce specific inhibitors targeting apicomplexan parasites. Moreover, potential DHO inhibitors exert beneficial effects on enzymatic activity of TgDHO and T. gondii growth in vitro. In conclusion, these data highlight the important role of TgDHO in parasite growth and reveal that it is a promising anti-parasitic target for future control of toxoplasmosis.

The apicoplast is important for the viability and persistence of Toxoplasma gondii bradyzoites

Toxoplasma gondii is responsible for toxoplasmosis, a disease that can be serious when contracted during pregnancy, but can also be a threat for immunocompromised individuals. Acute infection is associated with the tachyzoite form that spreads rapidly within the host. However, under stress conditions, some parasites can differentiate into cyst-forming bradyzoites, residing mainly in the central nervous system, retina and muscle. Because this latent form of the parasite is resistant to all currently available treatments, and is central to persistence and transmission of the parasite, specific therapeutic strategies targeting this developmental stage need to be found. T. gondii contains a plastid of endosymbiotic origin called the apicoplast, which is an appealing drug target because it is essential for tachyzoite viability and contains several key metabolic pathways that are largely absent from the mammalian host. Its function in bradyzoites, however, is unknown. Our objective was thus to study the contribution of the apicoplast to the viability and persistence of bradyzoites during chronic toxoplasmosis. We have used complementary strategies based on stage-specific promoters to generate conditional bradyzoite mutants of essential apicoplast genes. Our results show that specifically targeting the apicoplast in both in vitro or in vivo-differentiated bradyzoites leads to a loss of long-term bradyzoite viability, highlighting the importance of this organelle for this developmental stage. This validates the apicoplast as a potential area to look for therapeutic targets in bradyzoites, with the aim to interfere with this currently incurable parasite stage.

Comparative transcriptome profiling of Eimeria tenella in various developmental stages and functional analysis of an ApiAP2 transcription factor exclusively expressed during sporogony

BACKGROUND

The apicomplexan parasites Eimeria spp. are the causative agents of coccidiosis, a disease with a significant global impact on the poultry industry. The complex life cycle of Eimeria spp. involves exogenous (sporogony) and endogenous (schizogony and gametogony) stages. Unfortunately, the genetic regulation of these highly dynamic processes, particularly for genes involved in specific developmental phases, is not well understood.

METHODS

In this study, we used RNA sequencing (RNA-Seq) analysis to identify expressed genes and differentially expressed genes (DEGs) at seven time points representing different developmental stages of Eimeria tenella. We then performed K-means clustering along with co-expression analysis to identify functionally enriched gene clusters. Additionally, we predicted apicomplexan AP2 transcription factors in E. tenella using bioinformatics methods. Finally, we generated overexpression and knockout strains of ETH2_0411800 to observe its impact on E. tenella development.

RESULTS

In total, we identified 7329 genes that are expressed during various developmental stages, with 3342 genes exhibiting differential expression during development. Using K-means clustering along with co-expression analysis, we identified clusters functionally enriched for oocyte meiosis, cell cycle, and signaling pathway. Among the 53 predicted ApiAP2 transcription factors, ETH2_0411800 was found to be exclusively expressed during sporogony. The ETH2_0411800 overexpression and knockout strains did not exhibit significant differences in oocyst size or output compared to the parental strain, while the resulting ETH2_0411800 knockout parasite showed a relatively small oocyst output.

CONCLUSIONS

The findings of our research suggest that ETH2_0411800 is not essential for the growth and development of E. tenella. Our study provides insights into the gene expression dynamics and is a valuable resource for exploring the roles of transcription factor genes in regulating the development of Eimeria parasites.

A Plasmodium membrane receptor platform integrates cues for egress and invasion in blood forms and activation of transmission stages

Critical events in the life cycle of malaria-causing parasites depend on cyclic guanosine monophosphate homeostasis by guanylyl cyclases (GCs) and phosphodiesterases, including merozoite egress or invasion of erythrocytes and gametocyte activation. These processes rely on a single GCα, but in the absence of known signaling receptors, how this pathway integrates distinct triggers is unknown. We show that temperature-dependent epistatic interactions between phosphodiesterases counterbalance GCα basal activity preventing gametocyte activation before mosquito blood feed. GCα interacts with two multipass membrane cofactors in schizonts and gametocytes: UGO (unique GC organizer) and SLF (signaling linking factor). While SLF regulates GCα basal activity, UGO is essential for GCα up-regulation in response to natural signals inducing merozoite egress and gametocyte activation. This work identifies a GC membrane receptor platform that senses signals triggering processes specific to an intracellular parasitic lifestyle, including host cell egress and invasion to ensure intraerythrocytic amplification and transmission to mosquitoes.

Invasion of Toxoplasma gondii bradyzoites: Molecular dissection of the moving junction proteins and effective vaccination targets

Toxoplasmosis is a neglected parasitic disease necessitating public health control. Host cell invasion by Toxoplasma occurs at different stages of the parasite's life cycle and is crucial for survival and establishment of infection. In tachyzoites, which are responsible for acute toxoplasmosis, invasion involves the formation of a molecular bridge between the parasite and host cell membranes, referred to as the moving junction (MJ). The MJ is shaped by the assembly of AMA1 and RON2, as part of a complex involving additional RONs. While this essential process is well characterized in tachyzoites, the invasion process remains unexplored in bradyzoites, which form cysts and are responsible for chronic toxoplasmosis and contribute to the dissemination of the parasite between hosts. Here, we show that bradyzoites invade host cells in an MJ-dependent fashion but differ in protein composition from the tachyzoite MJ, relying instead on the paralogs AMA2 and AMA4. Functional characterization of AMA4 reveals its key role for cysts burden during the onset of chronic infection, while being dispensable for the acute phase. Immunizations with AMA1 and AMA4, alone or in complex with their rhoptry neck respective partners RON2 and RON2_L1, showed that the AMA1-RON2 pair induces strong protection against acute and chronic infection, while the AMA4-RON2_L1 complex targets more selectively the chronic form. Our study provides important insights into the molecular players of bradyzoite invasion and indicates that invasion of cyst-forming bradyzoites contributes to cyst burden. Furthermore, we validate AMA-RON complexes as potential vaccine candidates to protect against toxoplasmosis.