Characterization and Inductive Expression Analysis of Interferon Gamma-Related Gene in the Indian Major Carp, Rohu ( Labeo rohita )

Interferon gamma (IFN-γ) is one of the key cytokines that plays a major role against viral and intracellular bacterial infection. In addition to the IFN-γ gene, teleost fish possess a second copy known as IFN-γ-related (IFN-γrel) gene. This report describes structural and functional properties of IFN-γrel gene in the Indian major carp, rohu (Labeo rohita), a commercially important freshwater fish species in the Indian subcontinent. The rohu IFN-γrel gene consisted of four exons with three intervening introns and phylogenetically closely related to grass carp. The full-length IFN-γrel cDNA comprised 927 bp nucleotides with a single open reading frame of 504 bp, encoding 167 amino acids (aa) polypeptide with a signal peptide of 24 aa. The mature rohu IFN-γrel protein was 143 aa with a predicted molecular weight of 16.85 kDa. Basal expression analysis of IFN-γrel showed its wide range of expression in all examined tissues: The highest was in the skin and the lowest was in the liver. In response to LPS, poly I:C, iE-DAP, muramyl dipeptide stimulations, and bacterial infections, IFN-γrel gene expression was significantly (p<0.05) induced in treated fish tissues as compared with their control. The IFN-γrel was expressed as recombinant protein (rIFN-γrel) and confirmed through western blot. Stimulation of peripheral blood leukocytes with rIFN-γrel protein resulted in the activation of IFN-γ receptor and marked induction of inducible nitric oxide synthase gene expression. These results together may suggest the important role of IFN-γrel as an antimicrobial cytokine in fish.