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  • In the present study Asian


    In the present study, Asian swamp eel CXCR1a (MaCXCR1a), MaCXCR1b, MaCXCR2, MaCXCR3a, MaCXCR3b, and MaCXCR4 were identified from the Asian swamp eel genome. To explore the features and functions of these CXCRs, we focused on the identification and molecular characterization of MaCXCRs, and NMS-1286937 molecular analysis of the MaCXCRs were conducted following immune stimulations.
    Materials and methods
    Discussion Chemokines, or chemoattractant cytokines, are a family of cytokines that regulate immune cell migration under both inflammatory and normal physiological conditions [4]. CXCRs play important roles in the chemokine system [38]. Each CXCR protein may have distinct roles in the immune response. The Asian swamp eel is a commercially important cultured freshwater fish in China and other Asian countries [39,40]. A better understanding of the eel\'s immune responses may help to develop strategies for disease management, potentially improving yields and mitigating losses. Hence, in the current study, MaCXCR1-4 were identified and their expression patterns were analyzed to provide further insights into the functions of CXCRs in the Asian swamp eel.
    Acknowledgments This work research was financially supported by grants from Guangxi Key Laboratory of Marine Biotechnology, Guangxi Institute of Oceanology, Beihai (Grant No. GLMBT-201802), Hubei Provincial Department of Education (Grant No. B2016035), Engineering Research Center of Ecology and Agricultural Use of Wetland, Ministry of Education (Grant No. KF201709), and National Natural Science Foundation of China (Grant No. 31572626).
    Introduction Chemokine receptors interact with a group of peptide ligands of 8–10kDa and are indispensable for coordination of cell migration in diverse physiological processes such as development, angiogenesis, immune defence and neuroendocrine regulation. They belong to the largest rhodopsin family of G protein-coupled receptors (GPCRs), representing approximately 60% of the total GPCR repertoire (Fredriksson et al., 2003). Structurally each consists of 7 transmembrane domains and multiple extracellular and intracellular loops that are involved in ligand binding and signalling. Based on the ligand they bind, chemokine receptors are classified into four subgroups, the CC chemokine receptors (CCRs), CXCRs, XCRs and CX3CRs. In humans, 18 chemokine receptors, comprising 10 CCRs, 6 CXCRs, 1 XCR, and 1 CX3CR, have been characterised and act as receptors for at least 44 chemokine ligands (Zlotnik and Yoshie, 2012). An additional 4 atypical chemokine receptors (ACKRs) are known to scavenge ligands and suppress chemotactic responses elicited by chemokine receptors. The number of chemokine receptors varies considerably among vertebrate taxa, with fewer chemokine receptors found in birds and a large expansion seen in teleost species. With an increasing wealth of sequence data available from sequenced genomes and EST databases, this review will take a comparative approach to provide an update of the advances in chemokine receptor gene discovery, with a focus on fish CXCRs. The chemokine receptor family shares many common properties with other GPCR family members, including protein structure, the mode of action and shared downstream signalling pathways (Viola and Luster, 2008). They consist of an extracellular N-terminal region, three extracellular hydrophilic loops (ECLs), three intracellular loops (ICLs) and an intracellular C-terminal region. The N-terminal extracellular region, together with the first ECL, is the core domain that physically engages with chemokines and dictates specificity. Upon activation by ligands, the monomeric receptor or homodimeric/heterodimeric receptor complex undergoes conformational changes that initiates distinct cellular responses. A heterodimeric receptor complex can be formed by two members of the chemokine receptor family or with the distantly related GPCRs (Muñoz et al., 2012), e.g. CXCR1/CXCR2 (Wilson et al., 2005) and CXCR2/opioid receptor (Parenty et al., 2008). The cellular signalling pathways are complex and G protein (α, β and γ subunits) dependent or involve members of the Janus kinase and signal transducers and activators of transcription family (Vila-Coro et al., 1999, Vroon et al., 2006). Upon activation, the C-terminal region interacts with G proteins, leading to the replacement of GDP with GTP in the Gα subunit, the disassociation of Gα from Gβγ, and phosphorylation of the C terminal intracellular region by G protein-coupled receptor kinases (GRKs) (Reiter and Lefkowitz, 2006). With the involvement of β-arrestin, the uncoupling of the Gα subunit triggers immediate internalization of the receptors which are transported into the endosomes where they are either recycled to the cell surface or are delivered to lysosomes for degradation (Marchese, 2014). These events eventually lead to activation of genes that are associated with cell mobilisation, growth or death.