Chemokines are small, structurally related chemotactic cytokines characterized by the presence of conserved cysteine residues. In the present study, we identified the cDNA of a CXC chemokine from Oplegnathus fasciatus, designated as OfCXCL12. An open reading frame of 297 bp encoded a 98 amino acid peptide with a putative signal peptide of 23 amino acids. The CXC family-specific small cytokine domain (SCY), which is highly conserved among vertebrates, was located between residues 29 and 87. The characteristic conserved cysteine residues in the CXC motif of OfCXCL12 were separated by tyrosine (Y). Similar to other vertebrate CXCL12 proteins, OfCXCL12 also lacked the ELR motif and hence belongs to ELR(-) subfamily. Phylogenetic analysis revealed two distinct clades, consisting of fish and tetrapod CXCL12 homologs. Constitutive expression with significantly higher levels of OfCXCL12 mRNA transcription was detected in immune-related organs, including the head kidney, spleen, and kidney. Infection with bacterial and viral agents led to significant upregulation of mRNA expression in both the head kidney and spleen, in a stimulant-specific manner. Stimulation of peripheral blood leukocytes by the mitogen concanavalin-A significantly induced OfCXCL12 transcription. Results from the present study suggest an important role for OfCXCL12 in immune defense against bacterial and viral infection in rock bream.
Keywords: CXCL12; Chemokines; Immune challenge; mRNA expression.
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