Molecular and expression characterizations of interleukin-8 gene in large yellow croaker (Larimichthys crocea)

IL-8 plays a crucial role in acute inflammation by recruiting and mediating neutrophils and other cells and in initiating the oxidative burst in neutrophils and inducing wound healing by promoting angiogenesis. In the present study, the full-length cDNA and genome sequence of interleukin-8 (LcIL-8) were cloned from large yellow croaker Larimichthys crocea. The LcIL-8 cDNA sequence was 931 bp, containing a 118-bp 5'-untranslated region (UTR), a 528-bp 3'-UTR and a 285-bp open reading frame (ORF) which encoded 94 amino acids. A putative signal peptide including 20 amino acid residues was found at N-terminal in LcIL-8 protein. And a small cytokine (SCY) domain showing a typical CXC chemokine gene organization was predicted in LcIL-8. The genome sequence of LcIL-8 gene was composed of 1930 nucleotides, including four exons and three introns. Quantitative real-time PCR analysis indicated a broad expression of LcIL-8 in most detected tissues, with the most predominant expression in liver. After injection with LPS, Vibrio parahaemolyticus and poly I:C, LcIL-8 expression levels showed up-regulation in head-kidney and spleen. The peak value was in the spleen with 6 times (at 6 h) greater expression than in the control after LPS injection (p < 0.05). However, LcIL-8 transcripts showed down-regulation in the liver after all the three stimulants injection. Recombinant LcIL-8 mature peptide was produced by Escherichia coli, which enhanced the production of superoxide anion in PCK cells. In addition, 5 single-nucleotide polymorphisms (SNPs) were identified in LcIL-8 gene. The results suggested that LcIL-8 might play an important role in fish's immune response, and the SNPs might be used as potential candidate molecular markers for selection for disease-resistant large yellow croaker.