Sequence variation in Toxoplasma gondii MIC13 gene among isolates from different hosts and geographical locations

Toxoplasma gondii, an eukaryotic parasite of the phylum Apicomplexa, can infect almost any nucleated mammalian and avian cells. Micronemes are sub-cellular organelles of apicomplexan parasites which can secrete microneme proteins (MICs) playing a key role in the invasion process of T. gondii and are potential vaccine candidate molecules against toxoplasmosis. In this work, we examined sequence variation in T. gondii microneme protein 13 (TgMIC13) gene sequences among 18 isolates from different hosts and geographical locations by PCR amplification and subsequent sequence analysis. The complete TgMIC13 DNA and cDNA sequences were 2506-2507 and 1407 bp, respectively, and they were quite conserved among the T. gondii isolates, with intra-specific variation of only up to 0.84% (21/2507) for genomic DNA and up to 0.71% (10/1407) for cDNA sequences. Phylogenetic analysis using maximum parsimony (MP) revealed that the TgMIC13 DNA sequences were not able to provide an effective molecular marker for intra-species phylogenetic analysis and differential identification of T. gondii isolates from different hosts and geographical locations. However, the results demonstrated that sequence variation in TgMIC13 gene was quite low among different T. gondii isolates, which may be a useful feature as an anti-toxoplasmosis vaccine candidate molecule in further studies.   Key words: Toxoplasma gondii, toxoplasmosis, microneme protein 13 (MIC13), sequence variation, phylogenetic analysis.