EXPRESSION OF TOXOPLASMA-GONDII GENES IN THE CLOSELY-RELATED APICOMPLEXAN PARASITE NEOSPORA-CANINUM

We have established the feasibility of using Neospora caninum as a het erologous system for the expression of genes from the closely-related parasite Toxoplasma gondii. Plasmid constructs containing the lacZ gen e from Escherichia coli driven by T. gondii promoters were electropora ted into N. caninum parasites, and expression of beta-galactosidase (b eta-Gal) activity was assayed enzymatically. In transient assays, expr ession of beta-Gal driven by the GRA1 promoter was approximately 10-fo ld higher than the expression obtained with the SAG1 promoter. Enzyme activity was not detected when N. caninum parasites were transfected w ith a promoterless lacZ construct. Transfection of N. caninum with com plete genomic clones of SAG1 or GRAZ from T. gondii yielded parasites that transiently expressed the respective gene products, as detected b y immunofluorescence and Western blot. Additionally, these transiently expressed T. gondii proteins appeared by immunofluorescence localizat ion and Triton X-114 partitioning to be correctly targeted in both ext racellular and intracellular N. caninum parasites. Heterologous gene e xpression should be useful for studying the function of specific gene products and may facilitate the identification of genes responsible fo r the phenotypic differences observed between these two closely-relate d apicomplexan parasites. (C) 1997 Elsevier Science B.V.