Identification of differentially expressed genes and quantitative expression of complement genes in the liver of marine medaka Oryzias melastigma challenged with Vibrio parahaemolyticus

The innate immune system of fish is the primary defense against acute diseases. The marine medaka Oryzias melastigma has been shown to be a potential marine fish model for ecotoxicology, but little is known about the innate immune system of this small fish. In this study, suppression subtractive hybridization (SSH) was used to identify differentially expressed immune genes in the liver of O. melastigma infected with Vibrio parahaemolyticus. Among the 396 genes identified, based on NCBI BLAST search of the 1279 sequenced clones in the SSH libraries, 38 (9.6%) were involved in the immune process. Besides, genes involved in biological regulations (5.6%); cellular metabolism (24.7%); general response to stimuli (4.8%); cellular component organization (2.3%); signal transduction (2.5%) and transport process (2.8%) were also obtained. Ten complement component genes involved in four activation pathways were quantified (using q-PCR) and exhibited different patterns of transcription between the control and challenged individuals. The results reported upon here support the feasibility of developing O. melastigma as a marine model fish to understand the basic biological processes related to immune function and for immunotoxicological research. Findings of this study established a genetic platform for studying immune function using O. melastigma.