Molecular characterization and expression analysis of the IFN-gamma related gene (IFN-γrel) in grass carp Ctenopharyngodon idella

Interferon gamma (IFN-γ), the only member of the type II class of interferons, has been identified in teleost fish. In addition to the IFN-γ gene, fish possess an IFN-γ related gene (IFN-γrel) neighbouring the authentic IFN-γ gene in the genome. In the present study, the cDNA sequence encoding 167 amino acids of IFN-γrel and its genomic organization were identified in grass carp Ctenopharyngodon idella. The predicted protein sequence of grass carp IFN-γrel (gcIFN-γrel) showed 63% and 50% identities to zebrafish and common carp IFN-γrel (previously termed as IFN-γ1), respectively. The IFN-γrel gene consists of 4 exons, with 3 intervening introns, spanning approximately 2 kb of genomic sequence. The gcIFN-γrel gene did not contain any polymorphic DNA repeats in the introns. Realtime PCR analysis showed that grass carp reovirus induced a high and long lasting (from days 1 to 7) expression of gcIFN-γrel in spleen. The expression of gcIFN-γrel in blood, head kidney, trunk kidney and spleen was also increased by bacterial peptidoglycan (PGN), lipopolysaccharide (LPS) and the interferon inducer polyI:C. The highest induction of gcIFN-γrel expression by PGN was observed in spleen, then in blood and head kidney. Further analysis of the expression patterns of gcIFN-γrel and PGN receptors, nucleotide oligomerization domains (NOD) 1 and 2, may suggest that IFN-γrel was possibly activated in a NOD2-dependent mechanism.