MOLECULAR ISOLATION AND CHARACTERIZATION OFAN IMMUNE DEFICIENCY (IMD) HOMOLOG GENEFROM MACROBRACHIUM ROSENBERGII

Abstract

Immune deficiency (IMD) is a death domain-containing protein, which plays a crucial role as a key adaptor protein in the IMD signaling pathway, one of the most important mechanisms in response to the viral and bacterial invasion of invertebrates. In this present study, an IMD gene was identified from Macrobrachium rosenbergii (MrIMD). The open reading frame (ORF) of MrIMD was comprised of 555 nucleotides and encoded a protein consisting of 184 amino acids residues, with a conserved death domain at the C-terminus. The MrIMD protein demonstrated identity of 40-74% with the IMD homolog protein from other crustaceans, with the highest identity to MnIMD from M. nipponense. In addition, MrIMD protein also shared 12-20% identity with IMDs protein from insects. The phylogenetic analysis indicated that MrIMD was clustered with the IMDs from other crustacean species. Gene expression analysis revealed that the tissue distribution of MrIMD mRNA levels was expressed in all examined tissues, with the high expression observed in the gills and hepatopancreas. In immune challenge studies, different patterns of the MrIMD mRNA expression were found between bacterial and viral infections. After A. hydrophila stimulation, MrIMD was significantly up-regulated in muscle, gills, and intestines whilst no significant difference observed in the hemocyte and hepatopancreas compared to that of control group. Conversely, the MrIMD was dramatically up-regulated after the Macrobrachium rosenbergii nodavirus challenge in the muscle and hepatopancreas, whereas the expression was down-regulated in the gills. These results suggested that the MrIMD gene might have had a different role in response to Gram-negative bacteria and viral infection and plays a crucial role in innate immunity.-