Abstract
BACKGROUND: Chicken coccidiosis, caused by the infection of Eimeria species, leads to important economic losses to the poultry industry. Vaccination with attenuated live parasites seems to be the best way to control this disease. Attenuated eimerian parasites with shortened prepatent times show great changes in intracellular development compared to their parent strains but the mechanisms involved in these biological differences are still unclear. RESULTS: In this study, we obtained a precocious line of E. maxima by sequential selection of 22 generations of early shed oocysts in chickens and performed a comparative transcriptome analysis of three different developmental stages of the precocious line and its parent strain using Illumina high-throughput sequencing. Our E. maxima precocious line showed decreased pathogenicity, reduced fecundity and a greatly shorted prepatent time of only 98 h. We found that typical gene changes in the stage development from unsporulated to sporulated oocyst and from sporulated oocyst to merozoite were marked by upregulated organelle genes and protein translation related genes, respectively. Additionally, major differences between the precocious line and its parent strain were detected in the merozoite stage, characterized by downregulated genes involved in protein cleavage and DNA replication activities. CONCLUSIONS: Our study generated and characterized an E. maxima precocious line, illustrating gene expression landscapes during parasite development by transcriptome analysis. We also show that the suppressed DNA replication progress in the merozoite stage in the precocious line may result in its reduced fecundity. These results provide the basis for a better understanding of the mechanism of precocity in Eimeria species, which can be useful in studies in early gametocytogenesis in apicomplexan parasites.