Identification and expression analysis of goose-type lysozyme in half-smooth tongue sole (Cynoglossus semilaevis)

Lysozymes are considered to be potent innate immune molecules against the invasion of bacterial pathogens. The goose-type lysozyme is one of the three major distinct lysozyme types identified in the animal kingdom including teleosts. In this report, we identified, sequenced, and characterized the goose-type lysozyme gene (CsGLys) from half-smooth tongue sole (Cynoglossus semilaevis). The full-length cDNA of CsGLys is 1191 bp in length from the transcription start site to polyadenylation site, including a 91 bp 5'-terminal untranslated region (UTR), a 452 bp 3'-terminal UTR and a 648 bp open reading frame (ORF) of encoding a polypeptide with 215 amino acids. The deduced amino acid sequence of CsGLys possesses a Goose Egg White Lysozyme (GEWL) domain with three conserved residues (E91, D104 and D121) essential for catalytic activity. The CsGLys gene consisting of 2535 bp, was similar to those of other teleost species such as Japanese flounder and large yellow croaker with five exons interrupted by four introns. The 5'-flanking region of CsGLys gene shows several transcriptional factor binding sites related to immune response. Tissue expression profile analysis by quantitative real-time reverse transcription PCR showed that CsGLys mRNA was constitutively expressed in all examined tissues with the predominant expression in skin and the weakest expression in heart. The expression of CsGLys after challenged with bacteria Vibrio anguillarum was up-regulated in blood, head kidney, liver and spleen at 12 h post-infection and it reached the peak level at the same time point with a 19.89-, 4.21-, 14.45- and 10.37-fold increase, respectively, while the CsGLys expression was down-regulated to lower level than the normal level in each tested tissues except in liver from the 48 h until 96 h. These results suggest that CsGLys might play an important role in half-smooth tongue sole host defense against the bacteria infection.