Genome-wide identification, expression analysis and transcriptional regulation of major histocompatibility complex class I genes in mandarin fish Siniperca chuatsi

Major histocompatibility complex class I (MHC I) molecules, which are widespread across jawed vertebrates, are functional in initiating immune response by presenting antigens. In this study, a comprehensive analysis was performed to identify all possible MHC I genes in the mandarin fish (Siniperca chuatsi), with the finding of 12 MHC I genes, including 9 MHC I U lineage, 2 MHC I Z lineage genes and 1 (32m gene from the whole-genome database. These genes were constitutively expressed, with (32m showing higher expression level. Almost all MHC I genes and (32m were significantly upregulated in response to various immune stimuli, including Poly I:C, LPS, PGN, PHA, and Con A. It is further revealed that all MHC I genes except MHC I ZBA were responsive to type I and type II IFN stimulation. With dual-luciferase reporter assay, it was demonstrated that IRF1 and IRF2 can activate the proximal promoter reporter plasmids of U lineage genes and (32m, which all possess ISRE motifs. On the other hand, NLRC5 can activate the luciferase activity of promoter reporter plasmids for MHC I UBA1, MHC I UBA2, and (32m, all of which contain a conserved SXY regulatory motif. NLRC5 was also found to activate the promoter reporter plasmid for MHC I ZAA, which harbours an S box and a partially conserved X motif in its proximal promoter region. The results obtained in this study should have significant reference value for understanding MHC I gene composition and transcription in mandarin fish and also in other teleost fish, and for exploring the intricate relationship between polymorphism, disease resistance, and immune function of MHC I genes in mandarin fish.