Characterization of a novel CC chemokine CCL4 in immune response induced by nitrite and its expression differences among three populations of Megalobrama amblycephala

A novel CC chemokine gene, chemokine CC motif ligand 4 (CCL4), was isolated from Megalobrama amblycephala. The full-length cDNA was 913 bp, encoding 94 amino acid residues. The deduced amino acid sequence possessed the typical arrangement of four cysteines as found in other known CC chemokines. The expression of M. amblycephala CCL4 during the early development showed the mRNA levels before hatching and at 62 h post fertilized (hpf) were significantly higher than other post-hatching stages (P < 0.05). Besides, it was widely expressed in all detected tissues with the highest transcription in liver, followed by intestine, spleen and gill, where a larger number of immune cells including lymphocytes and macrophages are present. Our findings had fully confirmed that CCL4 expression was strongly induced in vitro and quickly up-regulated after nitrite stress, then substantially altered in all tested tissues, supporting a potential pro-inflammatory function. We also indicated that inflammation effect might firstly happen in blood after nitrite stress. Furthermore, the tissue expression differences of CCL4 among three natural populations revealed that CCL4 mRNA in Yuni Lake population was obviously higher than the other two populations, Liangzi Lake population and Poyang Lake population, which will provide valuable insights into breeding strategies for selecting population with better immune property of M. amblycephala.