Identification of endonuclease domain-containing 1 gene in Japanese flounder Paralichthys olivaceus

• The endonuclease domain-containing 1 gene (jf_ENDOD1) was identified in Japanese flounder.
• Jf_ENDOD1 mRNA levels were significantly up-regulated by bacterial formalin-killed cell (FKC) injection in many tissues.
• Jf_ENDOD1 recombinant protein digested DNA in vitro.
• DNase activities in total protein extracted from Japanese flounder spleen and kidney were increased post FKC injection.

The mRNA level of the endonuclease domain-containing 1 gene (Jf_ENDOD1) in Japanese flounder Paralichthys olivaceus kidney was significantly increased after injection of formalin-killed bacteria cells (FKC) in the previous microarray study. ENDOD1 is a member of the DNA/RNA non-specific nucleases family, and its role in fish immunity has not been reported. The open reading frame of Jf_ENDOD1 cDNA was 912 bp, encoding 303 amino acids. The first 27 amino acids were predicted to be a signal peptide and the mature Jf_ENDOD1 was calculated as 32 kDa. The amino acid sequence of Jf_ENDOD1 showed 76% identity to that of large yellow croaker Larimichthys crocea. Transcripts of Jf_ENDOD1 were marginally detected in all sampled tissues from healthy fish, while they were significantly detected in brain, kidney, spleen and intestine at 6 h post FKC injection. Jf_ENDOD1 recombinant protein produced in Escherichia coli showed DNase activity. Furthermore, to evaluate the DNase activities in vivo, total proteins from Japanese flounder kidney and spleen were extracted at 12, 24 and 72 h post Edwardsiella tarda FKC injection. The DNase activity of extracted protein was higher in treated fish than in untreated fish. Since the mRNA levels were significantly up-regulated after the FKC treatment, Jf_ENDOD1 might be responsible for the activities.