Unknown,Transcriptomics,Genomics,Proteomics

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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. 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.

ORGANISM(S): Toxoplasma gondii

SUBMITTER: Michael Behnke

PROVIDER: E-GEOD-24905 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Virulence differences in Toxoplasma mediated by amplification of a family of polymorphic pseudokinases.

Behnke Michael S MS Khan Asis A Wootton John C JC Dubey Jitender P JP Tang Keliang K Sibley L David LD

Proceedings of the National Academy of Sciences of the United States of America 20110517 23

The population structure of Toxoplasma gondii includes three highly prevalent clonal lineages referred to as 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 strain types. Here, we explored the genetic basis of differences in virulence between the highly virulent type I lineage and moderately virulent type II ba ...[more]

PMID: 21586633

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Project description:Toxoplasma gondii is an obligate intracellular protozoan parasite whose rapid lytic replication cycles define its pathogenicity. We identified a temperature sensitive growth mutant, FV-P6, which irreversibly arrests before the middle of the G1 stage of the tachyzoite cell cycle. This arrest is caused by a point mutation in a gene conserved across eukaryotes, Cactin, whose product localizes to the nucleus. To elucidate the role of TgCactin we performed genome-wide expression profiling of FV-P6 mutant parasites at 35C and 40C, as well as FV-P6 complemented with a wild-type Cactin encoding cosmid (TOXO93 or comp) and as a pseudo-diploid wild-type line encoding both the wild-type and mutant Cactin locus (S4.2), also at both temperatures. Besides the expected G1 expression profile, many genes associated with the extracellular state as well as with the bradyzoite cyst stage were identified. Consistent with these profiles were the expression of AP2 transcription factors typically associated with extracellular and bradyzoite stage parasites. This suggests a role for TgCactin in control of gene expression. Since TgCactin does not contain any functionally defined domains we reasoned TgCactin exerts its function through interactions with other proteins. In support of this model we demonstrated that TgCactin is present in a protein complex and can oligomerize. Taken together, these results suggest that TgCactin acts as a pivotal protein potentially regulating gene expression at several transition points in parasite development. The role of Cactin in G1 progression of Toxoplasma gondii tachyzoites was assessed by expression profiling a temperature senstive mutant of Cactin at both the permissive (35C) as well as the restrictive (40C) temperature. Controls under the same temperature conditions inlcude the mutant line complemented with a wild-type Cactin allele encoded on a cosmid and a wild-type parasite line expressing an additional, mutant allele of Cactin (pseudo-diploid line).

Dataset Information

Virulence differences in Toxoplasma mediated by amplification of polymorphic pseudokinases.

Publications

Virulence differences in Toxoplasma mediated by amplification of a family of polymorphic pseudokinases.

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