Molecular characterization and functional analysis of Eimeria tenella ankyrin repeat-containing protein

Chicken coccidiosis causes disastrous losses to the poultry industry all over the world. Eimeria tenella is the most prevalent of these disease-causing species. Our former RNA-seq indicated that E. tenella ankyrin repeat-containing protein (EtANK) was expressed differently between drug-sensitive (DS) and drug-resistant strains. In this study, we cloned EtANK and analyzed its translational and transcriptional levels using quantitative real-time PCR (qPCR) and western blotting. The data showed that EtANK was significantly upregulated in diclazuril-resistant (DZR) strains and maduramicin-resistant (MRR) strains compared with the drug-sensitive (DS) strain. In addition, the transcription levels in the DZR strains isolated from the field were higher than in the DS strain. The translation levels of EtANK were higher in unsporulated oocysts (UO) than in sporozoites (SZ), sporulated oocysts (SO), or second-generation merozoites (SM), and the protein levels in SM were significantly higher than in UO, SO, and SZ. The results of the indirect immunofluorescence localization showed that the protein was distributed mainly at the anterior region of SZ and on the surface and in the cytoplasm of SM. The fluorescence intensity increased further with its development in vitro. An anti-rEtANK polyclonal antibody inhibited the invasive ability of E. tenella in DF-1 cells. These results showed that EtANK may be related to host cell invasion, required for the parasite's growth in the host, and may be involved in the development of E. tenella resistance to some drugs.