Molecular cloning and expression analysis of g-type lysozyme gene from blout snout bream (Megahbrama amblycephala)

We cloned the cDNA encoding g-type lysozyme from blout snout bream (Megahbrama amblycephala) by using rapid amplication of cDNA ends (RACE) approach. The full length cDNA of g-type lysozyme was 719 bp, consisting of a 5 untranslated region of 71 bp, a 3 untranslated region of 90 bp and an open reading frame of 558 bp. Based on amino similarity comparison, the three catalytic sites and four substrate binding sites were highly conserved among different fishes, and phylogenetic tree analysis indicates that g-type lysozyme of M.amblycephala had close relationship with Ctenopharyngodon idella. Quantitative real-time PCR analysis shows that the g-type lysozyme gene was expressed in most tissues of M.amblycephala with highest expression in intestinal. After ammonia-N challenge and recovery, the relative expression levels of g-type lysozyme in liver and brain were higher than that in the control at 12th, 24th, 48th and 72nd hour of post-stress, followed by a gradual decrease at 72th hour of recovery. By contrast, the relative expression level of g-type lysozyme in gill was lower than that in the control from 3rd hour to 72nd hour of post-stress, but peaked at 72nd hour of recovery. It is speculuted that g-type lysozyme gene involved in molecular processes of ammonia-N stress.