MOLECULAR CLONING AND EXPRESSION ANALYSIS OF THE α AND γ SUBUNIT GENES OF FcγR IN RAINBOW TROUT (Oncorhynchus mykiss)

In this study, the cDNA sequences of FcγRα and FcRγ subunits of FcγR rainbow trout were cloned for the first time by RACE technique. The sequences of FcγRα and FcRγ were analyzed by using bioinformatics software. The expressions of the genes in different cell subpopulations and tissues, as well as in the head kidney after Poly (I鲶C) and lipopolysaccharide (LPS) stimulations were analyzed by real-time fluorescent quantitative polymerase chain reaction (PCR). The results showed that the full-length cDNA ofFcγRα is 1677 bp with an open reading frame (ORF) of 954 bp encoding 317 amino acids. The FcγRα is composed of a signal peptide and two Ig-like domains, however, without including transmembrane and intracellular regions. There are three kinds of FcγR subunit, involving FcRγ1, FcRγ2a, and FcRγ2b. FcRγ1 and FcRγ2 genes are located on different chromosomes, while FcRγ2a and FcRγ2b are two splicing isoforms of FcRγ2 gene. These subunits are composed of signal peptide, transmembrane domain, and immunoreceptor tyrosine-based activation motif (ITAM). Amino acid sequence similarity analysis showed that the highest identity (30%) of FcγRα is between rainbow trout and channel catfish (Ictalurus punctatus), and FcRγ1 and FcRγ2a/2b in rainbow trout have the maximum sequence identity (40%) with mammalian FcRγ. Tissue distribution analysis showed that the expression of FcγRα, FcRγ1, and FcRγ2a/2b was higher in head kidney, spleen, and blood cells, respectively. Analysis of cell subpopulations showed that the expression of FcγRα, FcRγ1, and FcRγ2a/2b was the highest in the myeloid cell population. In addition, the expression of FcγRα, FcRγ1, and FcRγ2a/2b in the head kidney was significantly up-regulated after LPS and Poly (I鲶C) stimulations, indicating that FcγR plays an important role in the antibacterial and antiviral immunity.