title: The role of DNA mismatch repair in generating genetic diversity and drug resistance in malaria parasites.
abstract: Although the mechanisms by which malaria parasites develop resistance to drugs are unclear, current knowledge suggests a main mechanism of resistance is the alteration of target enzymes by point mutation. In other organisms, defects in DNA mismatch repair have been linked to increased mutation rates and drug resistance. We have identified an unusual complement of mismatch repair genes in the Plasmodium genome. An initial functional test of two of these genes (PfMSH2-1 and PfMSH2-2) using a dominant mutator assay showed an elevation in mutation frequency with the PfMSH2-2 homolog, indirectly demonstrating a role for this gene in mismatch repair. We successfully disrupted PbMSH2-2 in the Plasmodium berghei laboratory isolate NK65, and showed that this gene is not essential for parasite growth in either the asexual (rodent) or sexual (mosquito) stages of the lifecycle. Although we observed some differences in levels of drug resistance between wild type and mutant parasites, no uniform trend emerged and preliminary evidence does not support a strong link between PbMSH2-2 disruption and dramatically increased drug resistance. We found microsatellite polymorphism in the PbMSH2-2 disrupted parasites in less than 40 life cycles post-transfection, but not in PbMap2K disrupted controls or mosquito-passaged wild type parasites, which suggests a possible role for PbMSH2-2 in preventing microsatellite slippage, similar to MSH2 in other organisms. Our studies suggest that Plasmodium species may have evolved a unique variation on the highly conserved system of DNA repair compared to the mismatch repair systems in other eukaryotes.
authors.affiliation: Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, United States. lara.bethke@icr.ac.uk
authors.forename: Lara
authors.initials: L
authors.lastname: Bethke
authors.forename: Susan
authors.initials: S
authors.lastname: Thomas
authors.forename: Kerone
authors.initials: K
authors.lastname: Walker
authors.forename: Ronak
authors.initials: R
authors.lastname: Lakhia
authors.forename: Radha
authors.initials: R
authors.lastname: Rangarajan
authors.forename: Dyann
authors.initials: D
authors.lastname: Wirth
mesh_terms: D000818:Animals; D053843:DNA Mismatch Repair; D004351:Drug Resistance / Q000235:genetics*; D014644:Genetic Variation; D018895:Microsatellite Repeats; D009154:Mutation; D009963:Orotic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D021261:Parasitic Sensitivity Tests; D010962:Plasmodium berghei / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D010963:Plasmodium falciparum / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011110:Polymorphism, Genetic; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D051381:Rats
chemical_list: D015800:Protozoan Proteins; D009963:Orotic Acid; C001242:5-fluoroorotic acid