CC chemokines and their receptors in black rockfish (Sebastes schlegelii): Characterization, evolutionary analysis, and expression patterns after Aeromonas Salmonicida infection

Chemokines are a superfamily of structurally related cytokines, which could interact with chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors, to play crucial roles in guiding cell mobilization in development, homeostasis, and immunity. Among them, the CC subfamily is the largest subfamily with several members. In the present study, 24 CC chemokine ligands and 12 CC chemokine receptors were systematically identified from Black rockfish (Sebastes schlegelii). Sequence analyses indicated that most CC chemokine ligands, located in extracellular region, possess SCY domain, and CC chemokine receptors, located in plasma membrane, harbored the seven-transmembrane-region domain. Subsequently, the phylogeny, synteny, genome organization, and evolutionary analyses were performed to annotate these genes, and revealed that the tandem duplications (CCL19, CCL20a, CCL32, CCL33, CCL36, CCL38, CCR2, and CCR8), the whole genome duplications (CCL20, CCL25, CCR6, CCR9, and CCR12), and the teleost-specific members (CCL32-36, CCL38, CCL39, CCL44, and CCR12) led to the expansion of CCLs and CCRs in S. schlegelii. In addition, CCLs and CCRs were ubiquitously expressed in nine examined healthy tissues, with high expression levels in gill, head kidney, and spleen. Moreover, most CCLs and CCRs were significantly differentially expressed in head kidney, liver, and gill after A. salmonicida infection, and their expression patterns exhibited tissue-specific and time-dependent manner. Finally, the protein-protein interaction network (PPI) analysis indicated that CCLs and CCRs interacted with a few immune-related genes such as interleukins, CD genes, and TLR genes, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines and receptors in teleost.