Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2009
Publication Date: October 5, 2009
Citation: Schwarz, R.S., Fetterer, R.H., Miska, K.B., Rosenberg, G.H. 2009. Coccidian Merozoite transcriptome analysis from Eimeria maxima in comparison to Eimeria tenella and Eimeria acervulina. Journal of Parasitology. 96:49-57. Interpretive Summary: Although coccidiosis disease in chickens, caused by 7 species of Eimeria parasites, causes significant economic loss to the poultry industry each year, effective means of protecting animals from this disease are hampered by resistance of the parasites against the repertoire of drugs currently used. No new drug targets have been identified, thus this is a novel area for research. In addition, consumer demands for pharmaceutical-free meat make vaccine development against these parasites a critical goal. The novelty of the research we present here is two-fold. First, we provide the first description of the genes expressed by one of the most abundant and pathogenic species, Eimeria maxima, using expressed sequence tag (EST) analysis. This is a basic but essential step that provides a foundation to further research into the biology of this species. Second, we provide the first comparative analysis of gene expression among the Eimeria species using the EST data we collected from E. maxima against the only other species for which gene expression information has been collected, E. tenella and E. acervulina. The significance and implications of our research are that the EST data has been annotated, where each gene/gene fragment has been identified according to similarity to previously identified genes, and made publicly available to other researchers via the GenBank database and a specific database we generated for this project. This data will help researchers gain insight into the genes expressed by this species and further the understanding of the biology of the parasite. In addition, our comparative analysis has resulted in the identification of a previously undescribed gene encoding a predicted protein that is a strong candidate for further analysis as a vaccine and drug target for the following reasons: 1) it is abundantly expressed in all three species of Eimeria, 2) it is unique to Eimeria, thus it is an ideal target since side effects to the host (chicken) are not likely to occur, 3) it has highly similar regions among all three species, thus a single vaccine or drug against this molecule may be cross-reactive to multiple species of Eimeria, rather than just against a single species.
Technical Abstract: Using the Eimeria spp. population that infect chickens as a model for coccidian biology, we aimed to survey the transcriptome of E. maxima and contrast it to the two other Eimeria spp. for which transcriptome data are available, E. tenella and E. acervulina. Examining specifically the asexual intracellular development stage, the merozoite, we used expressed sequence tag (EST) analysis to provide experimental evidence of transcription and a framework for understanding the merozoite stage of E. maxima. Of 2,680 individual ESTs obtained 48.2% shared significant (E<10-5) homology with sequences from other apicomplexan species, almost exclusively Toxoplasma gondii and Eimeria spp., while 47.5% were unique. Annotation of these ESTs enabled categorization to putative biological function and revealed an emphasis on translation, cytoskeleton, metabolism, signaling, transport, and protein folding as well as the apicomplexan specific components surface antigens and micronemes. Comparative analysis of abundantly expressed transcripts from merozoites of the three Eimeria spp. revealed a novel transcript common to all three. Sharing no significant homology to any other sequence in public databases, this transcript was predicted to encode an Eimeria-specific protein (ESP) with 166-178 amino acids and 58.9-65.1% interspecific identity. A predicted signal peptide was identified, consistent with the assumption that ESP is a secreted protein. These annotated ESTs from E. maxima merozoites provide a resource for intra- and interspecific comparative analyses that will be useful in distinguishing the unique biology of coccidian parasites in relation to the diverse phylum of Apicomplexa.