The DNA cytosine-5-methyltransferase 3 (DNMT3) involved in regulation of CgIL-17 expression in the immune response of oyster Crassostrea gigas

DNA methyltransferase, a key enzyme mediating DNA methylation, is involved in numerous processes including genomic imprinting, X chromosome inactivation, transposable element suppression, and immune defense in vertebrates. In the present study, a DNA cytosine-5-methyltransferase 3 was identified from oyster Crassostrea gigas (designed as CgDNMT3). There were a PWWP domain, a PHD domain and a DNA-methylase domain in the deduced amino acid sequences of CgDNMT3, and the conserved motifs I, IV, VI, VIII, IX and X were identified in its C-terminal catalytic DNA-methylase domain. The mRNA transcripts of CgDNMT3 were detected in haemocytes, mantle, gill, adductor muscle, digestive gland and labial palp, with higher expression level in haemocytes (6.54 folds of those in gill, p < 0.01). The expression level of CgDNMT3 mRNA in haemocytes increased significantly after LPS primed (2.87 folds of that in control group, p < 0.05) in vitro or Vibrio splendidus challenging (1.94 folds of that in control group, p < 0.05) in vivo. Immunocytochemical analysis revealed that CgDNMT3 protein was distributed mainly in cytoplasm and partial in nucleus of oyster haemocytes. After CgDNMT3 was transfected and expressed in HEK293T cells, the DNA 5-methylcytosine (5-mc) level in the transfected group was significantly increased, which was 1.22 folds (p < 0.05) of the pcDNA-3.1 group. The expressions of oyster CgIL17-1, CgIL17-2 and CgIL17-5 in haemocytes increased (13.05 folds, 4.78 folds and 9.41 folds of that in control group, respectively) at 12 h after V. splendidus challenging, but the increase were significantly inhibited when the oysters were pre-treated with DNA methyltransferase inhibitor 5-Azacytidine, which were 9 folds, 1.93 folds and 3.22 folds of that in control group, respectively. These results collectively suggested that CgDNMT3 was a conserved member of DNA methyltransferase 3 family in oyster, and participated in regulating the expression of cytokines during immune response.