Developmental regulation of an Eimeria bovis mRNA encoding refractile body-associated proteins

Eimeria bovis antigens defined by the monoclonal antibody (mAb) 2.4 are associated with the refractile bodies of sporozoites and are found in the parasitophorous vacuole and host cell cytoplasm during schizogony. Screening of an E. bovis oocyst cDNA library with mAb 2.4 resulted in the identification of a single unique cDNA sequence (Eb-25/50). Comparison of the predicted protein sequence of Eb-25/50 revealed a high degree of identity to an Eimeria tenella refractile body protein and mAb 2.4 was found to cross-react with refractile bodies from Eimeria acervulina, demonstrating that these proteins are highly conserved among eimerian species. Measurements of Eb-25/50 mRNA showed that the multiple proteins recognized by mAb 2.4 are encoded by a single mRNA species whose kinetics of expression during sporulation and schizogony closely correlated with protein expression. Consistent with multiple Eb-25/50 proteins arising from a single polypeptide, results from a Southern analysis of E. bovis genomic DNA indicated that Eb-25/50 mRNA is derived from a single copy gene. The presence of Eb-25/50 proteins in the host cytoplasm during schizogony, the high degree of conservation of these proteins, and the apparent complex post-translational modification raises interesting questions about the biochemistry of these proteins during eimerian development.