Molecular characterization of surface antigen 10 of Eimeria tenella

Chicken coccidiosis is caused by the apicomplexan parasite Eimeria spp. At present, drug resistance of Eimeria is common because of the indiscriminate use of anticoccidial drugs. The gene encoding surface antigen 10 of Eimeria tenella ( Et SAG10) is differentially expressed between drug-resistant and drug-sensitive strains. RNA-seq analysis indicated that this gene was downregulated in strains resistant to maduramicin and diclazuril compared to susceptible strains. Et SAG10 DNA sequence alignment revealed that they contained one and ten mutations in MRR and DZR, compared with DS, respectively. A full-length Et SAG10 cDNA was successfully cloned and expressed, and the polyclonal antibody was prepared. The transcription and translation levels of Et SAG10 were analyzed by quantitative real-time PCR (qPCR) and Western blotting. The localization of Et SAG10 in Spz, Mrz, and parasites in the first asexual stage was determined by indirect immunofluorescence. The potential association of Et SAG10 with sporozoite invasion of host cells was assessed by invasion inhibition assays. The results showed that Et SAG10 had a predicted transmembrane domain at the C-terminal end and a predicted signal peptide at the N-terminal end. Et SAG10 was downregulated in drug-resistant strains, which is consistent with the RNA-seq results. The Et SAG10 protein was localized to the parasite surface and parasitophorous vacuole membrane. This protein was shown to play a role in the infection of chicken intestine by sporozoites.