Senescent Eimeria acervulina Oocysts Maintain Transcriptional Activity During Extended Refrigerated Storage and Differentially Express Characteristic Genes

Enteric coccidian parasites harm agriculture and human health. Infectious, sporulated parasites eventually senesce. Here, we examined transcriptional changes in sporulated oocysts of Eimeria acervulina stored for 4–30 months at 4 °C. Precipitous decline in RNA abundance and transcription followed an interval of stability. Sixty constitutively expressed genes each contributed > 1000 transcripts per million (TPM) throughout, including a serine protease inhibitor, surface antigen genes, a cation-transporting ATPase, an oocyst wall protein, a zinc finger DHHC domain-containing protein, and highly expressed hypothetical proteins with no known function. Strikingly, ~82% of 6867 annotated genes underwent differential expression when comparing freshly sporulated parasites to those held for 30 months; nearly one-third of these underwent significant expression change. In freshly sporulated oocysts, 86 significantly DEGs exceeded 1000 TPM; these encoded heat shock proteins, lactate dehydrogenase, glucose-6 isomerase, and various hypothetical proteins. The oldest parasites expressed 66 DEGs, including many ribosomal subunits, a haloacid dehalogenase-like hydrolase domain-containing protein, and various hypothetical proteins. Taken together, these findings helped us to identify markers of mature parasites that remain relatively abundant in the transcript pool as oocysts age and identify other transcripts (e.g., ribosomal RNA) that increase in their relative abundance even as RNA abundance declines in senescent parasites.