Cloning, characterization and expression analysis of a CXCR1-like gene from mandarin fish Siniperca chuatsi

In this study we cloned and characterized a CXCR1-like gene (mfCXCR1) from mandarin fish (Siniperca chuatsi). The full-length cDNA of mfCXCR1 is 2,173 bp and contains a 1,056 bp open reading frame (ORF) that encodes a protein of 351 amino acids. The 5' and 3' untranslated regions (UTR) are 57 and 1,080 bp in length, respectively. The coding region of the mfCXCR1 gene consists of a single exon with a 734 bp intron that is two nucleotides upstream of the ATG start codon in the 5' UTR. The mfCXCR1 protein shares a relatively high identity with the CXCR1 and CXCR2 proteins of other fishes (similar to 50-65%). Furthermore, phylogenetic analysis indicates a close relatedness of mfCXCR1 to CXCR1 of other fishes. Many binding sites for stress-inducible transcription factors were present in the promoter region of the mfCXCR1 gene, indicating that it might be activated by certain stressors. The level of mfCXCR1 mRNA, when normalized to that in liver (1-fold), was highest in spleen (similar to 192.9-fold), with intermediate levels in kidney (similar to 163.2-fold), blood (similar to 131.2-fold) and head kidney (similar to 109.4-fold), and relatively low levels in intestine (similar to 34.4-fold) and gill (similar to 16.4-fold) (P < 0.05). Expression of mfCXCR1 during the clinical stage of infectious spleen and kidney necrosis virus (ISKNV) infection showed that its expression was regulated over the course of infection. On day 4 after ISKNV challenge, mfCXCR1 expression was down-regulated in blood (similar to 0.91-fold), spleen (similar to 0.26-fold), head kidney (similar to 0.18-fold) and kidney (similar to 0.82-fold).