Analysis of differentially expressed genes in the precocious line of Eimeria maxima and its parent strain using suppression subtractive hybridization and cDNA microarrays.

The precocious line of Eimeria spp., obtained by repeated passages of oocysts initially collected from feces of previously infected chickens, has unique phenotypes and plays an important role in immunizing chickens against coccidiosis. However, the genetic basis of precocious phenotype in Eimeria is still poorly understood. To investigate gene expression changes in sporulated oocysts between the precocious line of E. maxima and its parent strain, subtractive cDNA libraries were constructed by suppression subtractive hybridization (SSH). A total of 3,164 cDNA fragments were selected from the SSH cDNA libraries to fabricate cDNA microarrays and further identify the differentially expressed genes. The credibility of the microarray data was verified by real-time PCR. A total of 360 valid expressed sequence tags (ESTs) were obtained, which represented 32 unique sequences. Twenty-one genes were validated as downregulated and 11 genes as upregulated in the precocious line. Homology searching of the public sequence database showed that six genes encoded proteins homologous with previously reported proteins, including rhomboid-like protein and transhydrogenase of E. tenella, serpin, and cation-transporting ATPase of E. acervulina, a heat-shock protein of E. maxima, and a conserved hypothetical protein of Toxoplasma gondii. Thus, the remaining 26 ESTs have not been previously reported. Further characterization of these differentially expressed genes will be useful in understanding the genetic basis for the precocious phenotype in Eimeria spp.