CXC chemokine receptor 4 (CXCR4), a member of seven-transmembrane (7-TM) G-protein-coupled receptor superfamily, is the receptor of the CXC chemokine ligand 12 (CXCL12), and plays important roles in host defense and inflammation. In the current study, we cloned and identified a homolog of CXCR4 from Nile tilapia (Oreochromis niloticus), designated as OnCXCR4. The open reading frame of OnCXCR4 is 1149 bp encoding a peptide of 382 amino acids, and the predicted molecular weight is 42.65 kDa OnCXCR4 shares common features of CXCR4 family, including a 7-TM domain and a characteristic CXC motif (containing CYC). Expression analysis showed that OnCXCR4 constitutively expresses in various tested tissues of Nile tilapia, with the highest level in the anterior kidney. When stimulated with Streptococcus agalactiae, Aeromonas hydrophila, Poly(I:C), or LPS in vivo and in vitro, the expression of OnCXCR4 was significantly regulated. AMD3100, a CXCR4 antagonist, could not only inhibit the chemotactic activity of the recombinant OnCXCL12 protein on the leukocytes from anterior kidney, but also reduce the expression of OnCXCR4 significantly. Taken together, these results of our study above indicate that OnCXCR4 may play important roles in host defense against bacterial infectionin in Nile tilapia, and being a receptor of OnCXCL12 to exert functions.

CXC 趋化因子受体 4 (CXCR4) 是七跨膜 (7-TM) G 蛋白偶联受体超家族的成员，是 CXC 趋化因子配体 12 (CXCL12) 的受体，在宿主防御和炎症中起重要作用。在目前的研究中，我们从尼罗罗非鱼（Oreochromis niloticus）中克隆并鉴定了CXCR4的同源物，命名为OnCXCR4。OnCXCR4的开放阅读框为 1149 bp，编码 382 个氨基酸的肽段，预测分子量为 42.65 kDa 表达分析表明OnCXCR4在尼罗罗非鱼的各种测试组织中组成型表达，在前肾中水平最高。当在体内和体外用无乳链球菌、嗜水气单胞菌、Poly(I:C)或LPS刺激时， OnCXCR4的表达被显着调节。CXCR4拮抗剂AMD3100不仅能抑制重组OnCXCL12蛋白对前肾白细胞的趋化活性，还能降低OnCXCR4的表达显着地。综上所述，以上研究结果表明，OnCXCR4可能在尼罗罗非鱼的宿主防御细菌感染中发挥重要作用，并且是OnCXCL12的受体发挥功能。