Multiple pathways for glucose phosphate transport and utilization support growth of Cryptosporidium parvum

Impact of predicted microbiota tryptophanase activity on Cryptosporidium parvum proliferation

Protozoa in the genus Cryptosporidium infect intestinal epithelial cells. The profile of the fecal microbiota has been shown to impact the proliferation of Cryptosporidium parvum in a mouse model of cryptosporidiosis and a reverse effect of the parasite on the microbiota has also been described. The mechanisms underlying this interaction are unknown. The lack of effective drugs and vaccines is motivating the search for pro- or prebiotics capable of increasing resistance to parasite proliferation in the gastrointestinal tract. To understand if and how the intestinal microbiota could be harnessed for this purpose, we tested if C. parvum proliferation in the mouse responds to oral administration of Escherichia coli. This bacterium was chosen because of its reported importance in mediating colonization resistance, because it encodes tryptophanase, an enzyme which converts tryptophan into indole, and because of the availability of an ampicillin-resistant strain expressing green fluorescent protein. Excretion of GFP+ E. coli in the feces was highly variable among mice, a phenomenon which is also observed with C. parvum. A positive correlation between fecal output of probiotic E. coli and C. parvum was observed. This finding may indicate that intestinal colonization with two microorganisms as different as E. coli and C. parvum responds to the same conditions in the GI tract. Consistent with an effect of the microbiota on cryptosporidiosis, the pre-infection microbiota taxonomic profile was predictive of mouse susceptibility to C. parvum. Contrary to the reported inhibitory effect of indole on C. parvum, microbiota indole production potential was positively correlated with C. parvum fecal output. The effect of cryptosporidiosis on the microbiota was characterized by an expansion of facultative anaerobes, particularly Gammaproteobacteria. This study is a first attempt to assess the proliferation in the mouse of a defined probiotic and quantify its effect on C. parvum development.

Function of the alternative electron transport chain in the Cryptosporidium parvum mitosome

Cryptosporidium parvum and C. hominis possess a remanent mitochondrion called the mitosome, which lacks DNA, the tricarboxylic acid cycle, a conventional electron transport chain, and ATP synthesis. The mitosome retains ubiquinone and iron sulfur cluster biosynthesis pathways, both of which require protein import that relies on the membrane potential. It was previously proposed that the membrane potential is generated by electrons transferred through an alternative respiratory pathway coupled to a transhydrogenase (TH) that pumps hydrogens out of the mitosome. This pathway relies on an alternative oxidase (AOX) and type II NADH dehydrogenase (NDH2), which also exists in plants, some fungi, and several protozoan parasites. To examine this model, we determined the location and function of AOX and NDH2 in C. parvum. Surprisingly, we observed that NDH2 was localized to parasite surface membranes instead of the mitosome. Furthermore, a Δndh2 knockout (KO) strain was readily obtained, indicating that this protein is not essential for parasite growth. Although, AOX exhibited a mitosome-like staining pattern, we readily obtained an Δaox knockout strain, indicating that AOX is also dispensable for parasite growth. The growth of the Δaox strain was inhibited by the AOX inhibitors SHAM and 8-HQ to the same extent as wild type, indicating that AOX is not the target of these inhibitors in C. parvum. Collectively, our studies indicate that NDH2 and AOX are non-essential genes in C. parvum, necessitating an alternative mechanism for maintaining the mitosome membrane potential.

Importance

Cryptosporidiosis is the leading cause of diarrhea in young children and immunocompromised individuals, particularly AIDS/HIV patients. The only FDA approved drug against cryptosporidiosis, nitazoxanide, has limited effectivity in immunocompromised patients and is not approved for usage in children under 1 year old. Genomic analysis and previous studies proposed an alternative respiration pathway involving alternative oxidase (AOX) and type II NAD(P)H dehydrogenase (NDH2), which are thought to generate the mitosome membrane potential in C. parvum. Additionally, AOX and NDH2 were nominated as potential drug targets, based on their absence in mammalian hosts and sensitivity of parasite growth to known inhibitors of AOX. However, our study demonstrated that NDH2 is not localized in mitosome, AOX non-essential for parasite growth, and knockout lines lacking this enzyme are equally sensitive to AOX inhibitors. These findings indicate that AOX and NDH2 are not ideal candidates for future drug development against cryptosporidiosis and force a re-evaluation for models of how the mitosome generate its membrane potential.

γ-tubulin complex controls the nucleation of tubulin-based structures in Apicomplexa

Apicomplexan parasites rely on tubulin structures throughout their cell and life cycles, particularly in the polymerization of spindle microtubules to separate the replicated nucleus into daughter cells. Additionally, tubulin structures, including conoid and subpellicular microtubules, provide the necessary rigidity and structure for dissemination and host cell invasion. However, it is unclear whether these tubulin structures are nucleated via a highly conserved γ-tubulin complex or through a specific process unique to apicomplexans. This study demonstrates that Toxoplasma γ-tubulin is responsible for nucleating spindle microtubules, akin to higher eukaryotes, facilitating nucleus division in newly formed parasites. Interestingly, γ-tubulin colocalizes with nascent conoid and subpellicular microtubules during division, potentially nucleating these structures as well. Loss of γ-tubulin results in significant morphological defects due to impaired nucleus scission and the loss of conoid and subpellicular microtubule nucleation, crucial for parasite shape and rigidity. Additionally, the nucleation process of tubulin structures involves a concerted action of γ-tubulin and Gamma Tubulin Complex proteins (GCPs), recapitulating the localization and phenotype of γ-tubulin. This study also introduces new molecular markers for cytoskeletal structures and applies iterative expansion microscopy to reveal microtubule-based architecture in Cryptosporidium parvum sporozoites, further demonstrating the conserved localization and probable function of γ-tubulin in Cryptosporidium.

Optimization of a DiCre recombinase system with reduced leakage for conditional genome editing of Cryptosporidium

BACKGROUND

The dimerizable Cre recombinase system (DiCre) exhibits increased leaky activity in Cryptosporidium, leading to unintended gene editing in the absence of induction. Therefore, optimization of the current DiCre technique is necessary for functional studies of essential Cryptosporidium genes.

METHODS

Based on the results of transcriptomic analysis of Cryptosporidium parvum stages, seven promoters with different transcriptional capabilities were screened to drive the expression of Cre fragments (FKBP-Cre59 and FRB-Cre60). Transient transfection was performed to assess the effect of promoter strength on leakage activity. In vitro and in vivo experiments were performed to evaluate the leaky activity and cleavage efficiency of the optimized DiCre system by polymerase chain reaction (PCR), nanoluciferase, and fluorescence analyses.

RESULTS

The use of promoters with lower transcriptional activity, such as pcgd6_4110 and pcgd3_260, as opposed to strong promoters such as pActin, pα-Tubulin, and pEnolase, reduced the leakage rate of the system from 35-75% to nearly undetectable levels, as verified by transient transfection. Subsequent in vitro and in vivo experiments using stable lines further demonstrated that the optimized DiCre system had no detectable leaky activity. The system achieved 71% cleavage efficiency in vitro. In mice, a single dose of the inducer resulted in a 10% conditional gene knockout and fluorescent protein expression in oocysts. These fluorescently tagged transgenic oocysts could be enriched by flow sorting for further infection studies.

CONCLUSIONS

A DiCre conditional gene knockout system for Cryptosporidium with good cleavage efficiency and reduced leaky activity has been successfully established.

Treating cryptosporidiosis: A review on drug discovery strategies

Despite several decades of research on therapeutics, cryptosporidiosis remains a major concern for human and animal health. Even though this field of research to assess antiparasitic drug activity is highly active and competitive, only one molecule is authorized to be used in humans. However, this molecule was not efficacious in immunocompromised people and the lack of animal therapeutics remains a cause of concern. Indeed, the therapeutic arsenal needs to be developed for both humans and animals. Our work aims to clarify research strategies that historically were diffuse and poorly directed. This paper reviews in vitro and in vivo methodologies to assess the activity of future therapeutic compounds by screening drug libraries or through drug repurposing. It focuses on High Throughput Screening methodologies (HTS) and discusses the lack of knowledge of target mechanisms. In addition, an overview of several specific metabolic pathways and enzymatic activities used as targets against Cryptosporidium is provided. These metabolic processes include glycolytic pathways, fatty acid production, kinase activities, tRNA elaboration, nucleotide synthesis, gene expression and mRNA maturation. As a conclusion, we highlight emerging future strategies for screening natural compounds and assessing drug resistance issues.

Transcriptional control of the Cryptosporidium life cycle

The parasite Cryptosporidium is a leading agent of diarrhoeal disease in young children, and a cause and consequence of chronic malnutrition1,2. There are no vaccines and only limited treatment options3. The parasite infects enterocytes, in which it engages in asexual and sexual replication4, both of which are essential to continued infection and transmission. However, their molecular mechanisms remain largely unclear5. Here we use single-cell RNA sequencing to reveal the gene expression programme of the entire Cryptosporidium parvum life cycle in culture and in infected animals. Diverging from the prevailing model6, we find support for only three intracellular stages: asexual type-I meronts, male gamonts and female gametes. We reveal a highly organized program for the assembly of components at each stage. Dissecting the underlying regulatory network, we identify the transcription factor Myb-M as the earliest determinant of male fate, in an organism that lacks genetic sex determination. Conditional expression of this factor overrides the developmental program and induces widespread maleness, while conditional deletion ablates male development. Both have a profound impact on the infection. A large set of stage-specific genes now provides the opportunity to understand, engineer and disrupt parasite sex and life cycle progression to advance the development of vaccines and treatments.

Mendelian segregation and high recombination rates facilitate genetic analyses in Cryptosporidium parvum

Very little is known about the process of meiosis in the apicomplexan parasite Cryptosporidium despite the essentiality of sex in its life cycle. Most cell lines only support asexual growth of Cryptosporidium parvum (C. parvum), but stem cell derived intestinal epithelial cells grown under air-liquid interface (ALI) conditions support the sexual cycle. To examine chromosomal dynamics during meiosis in C. parvum, we generated two transgenic lines of parasites that were fluorescently tagged with mCherry or GFP on chromosomes 1 or 5, respectively. Infection of ALI cultures or Ifngr1-/- mice with mCherry and GFP parasites resulted in cross-fertilization and the formation of "yellow" oocysts, which contain 4 haploid sporozoites that are the product of meiosis. Recombinant oocysts from the F1 generation were purified and used to infect HCT-8 cultures, and phenotypes of the progeny were observed by microscopy. All possible phenotypes predicted by independent segregation were represented equally (~25%) in the population, indicating that C. parvum chromosomes exhibit a Mendelian inheritance pattern. The most common pattern observed from the outgrowth of single oocysts included all possible parental and recombinant phenotypes derived from a single meiotic event, suggesting a high rate of crossover. To estimate the frequency of crossover, additional loci on chromosomes 1 and 5 were tagged and used to monitor intrachromosomal crosses in Ifngr1-/- mice. Both chromosomes showed a high frequency of crossover compared to other apicomplexans with map distances (i.e., 1% recombination) of 3-12 kb. Overall, a high recombination rate may explain many unique characteristics observed in Cryptosporidium spp. such as high rates of speciation, wide variation in host range, and rapid evolution of host-specific virulence factors.

Unlocking the mystery of the feeder organelle and versatile energy metabolism in Cryptosporidium parvum

Xu and colleagues recently revealed the critical role of Cryptosporidium's feeder organelle in nutrient uptake, showcasing the parasite's ability to harness glucose and glucose-6-phosphate from host cells. This illuminates the sophisticated energy metabolism and survival strategies of the parasite, highlighting potential therapeutic targets.

Mendelian segregation and high recombination rates facilitate genetic analyses in Cryptosporidium parvum

Very little is known about the process of meiosis in the apicomplexan parasite Cryptosporidium despite the essentiality of sex in its life cycle. Most cell lines only support asexual growth of Cryptosporidium parvum (C. parvum), but stem cell derived intestinal epithelial cells grown under air-liquid interface (ALI) conditions support the sexual cycle. To examine chromosomal dynamics during meiosis in C. parvum, we generated two transgenic lines of parasites that were fluorescently tagged with mCherry or GFP on chromosomes 1 or 5, respectively. Infection of ALI cultures or Ifngr1-/- mice with mCherry and GFP parasites produced "yellow" oocysts generated by cross-fertilization. Outcrossed oocysts from the F1 generation were purified and used to infect HCT-8 cultures, and phenotypes of the progeny were observed by microscopy. All possible phenotypes predicted by independent segregation were represented equally (~25%) in the population, indicating that C. parvum chromosomes exhibit a Mendelian inheritance pattern. Unexpectedly, the most common pattern observed from the outgrowth of single oocysts included all possible parental and recombinant phenotypes derived from a single meiotic event, suggesting a high rate of crossover. To estimate the frequency of crossover, additional loci on chromosomes 1 and 5 were tagged and used to monitor intrachromosomal crosses in Ifngr1-/- mice. Both chromosomes showed a high frequency of crossover compared to other apicomplexans with map distances (i.e., 1% recombination) of 3-12 kb. Overall, a high recombination rate may explain many unique characteristics observed in Cryptosporidium spp. such as high rates of speciation, wide variation in host range, and rapid evolution of host-specific virulence factors.