title: Type II Toxoplasma gondii KU80 knockout strains enable functional analysis of genes required for cyst development and latent infection.
abstract: Type II Toxoplasma gondii KU80 knockouts (Δku80) deficient in nonhomologous end joining were developed to delete the dominant pathway mediating random integration of targeting episomes. Gene targeting frequency in the type II Δku80 Δhxgprt strain measured at the orotate (OPRT) and the uracil (UPRT) phosphoribosyltransferase loci was highly efficient. To assess the potential of the type II Δku80 Δhxgprt strain to examine gene function affecting cyst biology and latent stages of infection, we targeted the deletion of four parasite antigen genes (GRA4, GRA6, ROP7, and tgd057) that encode characterized CD8(+) T cell epitopes that elicit corresponding antigen-specific CD8(+) T cell populations associated with control of infection. Cyst development in these type II mutant strains was not found to be strictly dependent on antigen-specific CD8(+) T cell host responses. In contrast, a significant biological role was revealed for the dense granule proteins GRA4 and GRA6 in cyst development since brain tissue cyst burdens were drastically reduced specifically in mutant strains with GRA4 and/or GRA6 deleted. Complementation of the Δgra4 and Δgra6 mutant strains using a functional allele of the deleted GRA coding region placed under the control of the endogenous UPRT locus was found to significantly restore brain cyst burdens. These results reveal that GRA proteins play a functional role in establishing cyst burdens and latent infection. Collectively, our results suggest that a type II Δku80 Δhxgprt genetic background enables a higher-throughput functional analysis of the parasite genome to reveal fundamental aspects of parasite biology controlling virulence, pathogenesis, and transmission.
authors.affiliation: Department of Microbiology and Immunology, Dartmouth Medical School, 1 Medical Center Dr., Lebanon, NH 03756, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Fox
authors.forename: Alejandra
authors.initials: A
authors.lastname: Falla
authors.forename: Leah M
authors.initials: LM
authors.lastname: Rommereim
authors.forename: Tadakimi
authors.initials: T
authors.lastname: Tomita
authors.forename: Jason P
authors.initials: JP
authors.lastname: Gigley
authors.forename: Corinne
authors.initials: C
authors.lastname: Mercier
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Cesbron-Delauw
authors.forename: Louis M
authors.initials: LM
authors.lastname: Weiss
authors.forename: David J
authors.initials: DJ
authors.lastname: Bzik
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics* / Q000378:metabolism; D016827:CD8 Antigens / Q000276:immunology / Q000378:metabolism; D003141:Communicable Diseases / Q000382:microbiology; D017353:Gene Deletion; D055786:Gene Knockout Techniques; D018390:Gene Targeting; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D014122:Toxoplasma / Q000235:genetics* / Q000378:metabolism*; D014124:Toxoplasmosis, Animal / Q000469:parasitology*
chemical_list: D000953:Antigens, Protozoan; D016827:CD8 Antigens; C079248:GRA4 protein, Toxoplasma gondii; C095047:GRA6 protein, Toxoplasma gondii; D015800:Protozoan Proteins