title: Reassessment of the role of aromatic amino acid hydroxylases and the effect of infection by Toxoplasma gondii on host dopamine.
abstract: Toxoplasma gondii infection has been described previously to cause infected mice to lose their fear of cat urine. This behavioral manipulation has been proposed to involve alterations of host dopamine pathways due to parasite-encoded aromatic amino acid hydroxylases. Here, we report successful knockout and complementation of the aromatic amino acid hydroxylase AAH2 gene, with no observable phenotype in parasite growth or differentiation in vitro and in vivo. Additionally, expression levels of the two aromatic amino acid hydroxylases were negligible both in tachyzoites and in bradyzoites. Finally, we were unable to confirm previously described effects of parasite infection on host dopamine either in vitro or in vivo, even when AAH2 was overexpressed using the BAG1 promoter. Together, these data indicate that AAH enzymes in the parasite do not cause global or regional alterations of dopamine in the host brain, although they may affect this pathway locally. Additionally, our findings suggest alternative roles for the AHH enzymes in T. gondii, since AAH1 is essential for growth in nondopaminergic cells.
authors.affiliation: Department of Molecular Microbiology, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Zi T
authors.initials: ZT
authors.lastname: Wang
authors.affiliation: Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Harmon
authors.affiliation: Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Karen L
authors.initials: KL
authors.lastname: O'Malley
authors.affiliation: Department of Molecular Microbiology, School of Medicine, Washington University in St. Louis, St. Louis, Missouri, USA sibley@wustl.edu.
authors.forename: L David
authors.initials: LD
authors.lastname: Sibley
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002415:Cats; D004298:Dopamine / Q000378:metabolism; D005260:Female; D017353:Gene Deletion; D015870:Gene Expression; D006790:Host-Parasite Interactions; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics; D008018:Life Cycle Stages; D051379:Mice; D006899:Mixed Function Oxygenases / Q000172:deficiency / Q000235:genetics*; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D014122:Toxoplasma / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D014124:Toxoplasmosis, Animal / Q000378:metabolism* / Q000469:parasitology
chemical_list: D007527:Isoenzymes; D015800:Protozoan Proteins; D006899:Mixed Function Oxygenases; D004298:Dopamine