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Virulence differences in Toxoplasma mediated by amplification of polymorphic pseudokinases.

ABSTRACT: The population structure of Toxoplasma gondii includes three highly prevalent clonal lineages, types I, II, and III, which differ greatly in virulence in the mouse model. Previous studies have implicated a family of serine threonine protein kinases found in rhoptries (ROPs) as important in mediating virulence differences between types I vs. III and II vs. III. Here, we explored the genetic basis of differences in virulence between the highly virulent type I lineage and moderately virulent type II based on a new genetic cross and linkage mapping. Genome-wide association revealed a single quantitative trait locus controls the > 4 log difference in lethality between these strains. Neither ROP16 nor ROP18, previously implicated in virulence differences in T. gondii, were found to contribute to differences between types I and II. Instead, the major virulence locus contained a cluster of pseudokinases denoted as rhoptry protein 5 (ROP5); this locus contains a tandem cluster of polymorphic alleles that differed in expression levels between strains. ROP5 alleles contained only part of the catalytic triad of canonical S/T kinases, and consistent with this they lack demonstrable kinase activity in vitro. Genetic disruption of the rop5 locus in the type I lineage lead to a > 5 log increase in the lethal dose, and surviving mice developed lasting immunity and were protected from an otherwise lethal challenge. These findings reveal that amplification of a polymorphic cluster of pseudokinases plays an important role in pathogenesis of toxoplasmosis in the mouse model.

ORGANISM(S): Toxoplasma gondii

PROVIDER: GSE24905 | GEO | 2011/05/03

SECONDARY ACCESSION(S): PRJNA132095

REPOSITORIES: GEO

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Project description:The population structure of Toxoplasma gondii includes three highly prevalent clonal lineages, types I, II, and III, which differ greatly in virulence in the mouse model. Previous studies have implicated a family of serine threonine protein kinases found in rhoptries (ROPs) as important in mediating virulence differences between types I vs. III and II vs. III. Here, we explored the genetic basis of differences in virulence between the highly virulent type I lineage and moderately virulent type II based on a new genetic cross and linkage mapping. Genome-wide association revealed a single quantitative trait locus controls the > 4 log difference in lethality between these strains. Neither ROP16 nor ROP18, previously implicated in virulence differences in T. gondii, were found to contribute to differences between types I and II. Instead, the major virulence locus contained a cluster of pseudokinases denoted as rhoptry protein 5 (ROP5); this locus contains a tandem cluster of polymorphic alleles that differed in expression levels between strains. ROP5 alleles contained only part of the catalytic triad of canonical S/T kinases, and consistent with this they lack demonstrable kinase activity in vitro. Genetic disruption of the rop5 locus in the type I lineage lead to a > 5 log increase in the lethal dose, and surviving mice developed lasting immunity and were protected from an otherwise lethal challenge. These findings reveal that amplification of a polymorphic cluster of pseudokinases plays an important role in pathogenesis of toxoplasmosis in the mouse model. We used a new genotyping protocol based on hybridization of parental and recombinant progeny genomic DNA (gDNA) to Affymetrix gene arrays constructed for T. gondii (http://ancillary.toxodb.org/docs/Array-Tutorial.html). We identified 1,603 single feature polymorphisms (SFP) based on probes that successfully discriminated perfect match (type II) from mismatch (type I) hybridization across all clones and provided reliable SFP markers for this cross.

Project description:Phosphorylation is a regulatory mechanism by which intracellular apicomplexan parasites control the process of invading and modifying host cells. However, the sporulated oocysts’ phosphoprotein repertoires between virulent and avirulent strains of Toxoplasma gondii and the underlying mechanisms contributing to virulence is still a mystery. A quantitative analysis of the sporulated oocysts’ phosphoproteome profile of T. gondii virulent and avirulent strains belonging to different genotypes was conducted to reveal phosphoprotein expression patterns that contribute to the virulence of a particular phenotype. Phosphopeptides from the sporulated oocysts of the virulent strain PYS (Chinese ToxoDB#9) and the avirulent strain type II (PRU strain) were enriched by titanium dioxide (TiO2) affinity chromatography and quantified using iBT technology. A total of 10,645 unique phosphopeptides, 8,181 nonredundant phosphorylation sites and 2,792 phosphoproteins were identified. The quantitative analysis identified 4,129 differentially expressed phosphopeptides (DEPs) between sporulated oocysts of the PYS strain and PRU strain (|log1.5 fold change| > 1 and P < 0.05), including 2,485 upregulated and 1,644 downregulated phosphopeptides. Motif analysis identified 24 motifs from the upregulated phosphorylated peptides including 22 serine motifs and two threonine motifs (TPE and TP), and 15 motifs from the downregulated phosphorylated peptides including 12 serine motifs and three threonine motifs (TP, RxxT and KxxT) in PYS strain when comparing PYS/PRU. Several kinases were consistent with motifs of overrepresented phosphopeptides, such as PKA, PKG, CKII, IKK, MAPK, EGFR, INSR, Jak, Syk, Src, Ab1. GO analysis, KEGG pathway analysis and STRING analysis revealed differentially expressed phosphoproteins (DEPs) exhibiting significant functional properties. Kinase associated network analysis showed that AGC kinase had the greatest connected peptides. Our findings reveal significant difference in phosphopeptides of sporulated oocysts between virulent and avirulent T. gondii strains, which provides solid foundation for further exploring the mechanisms contributing to the virulence of T. gondii.

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Virulence differences in Toxoplasma mediated by amplification of polymorphic pseudokinases.

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