Molecular characterization, genomic structure and expressional profiles of a CXC chemokine receptor 4 (CXCR4) from rock bream Oplegnathus fasciatus

•OfCXCR4 was identified and cloned.•OfCXCR4 was a bi-exonic gene.•Higher levels of OfCXCR4 transcripts were detected mainly in immune organs.•OfCXCR4 expression dynamics is modulated by both bacterial and viral challenges.

The CXC chemokine receptor 4 (CXCR4) is the cognate receptor of the CXC chemokine ligand 12 (CXCL12) and plays a pivotal role under immune-pathophysiological conditions. In the current study, the CXCR4 homolog of Oplegnathus fasciatus (OfCXCR4) was sequenced and the mRNA expression levels were characterized. The genomic structure of the cloned OfCXCR4 coding region (2094 bp) revealed a bi-exonic element, where the open reading frame (ORF) appears split by a single intron. Analysis of the ORF (1134 bp) of OfCXCR4 revealed a predicted protein of 42.1 kDa with typical seven transmembrane (TM) domain architecture and several conserved structural features, including two cysteine residues forming a predicted disulfide bond, a characteristic CXC motif (containing CYC) and a G-protein-coupled receptor (GPCR) family 1 signature. Furthermore, based on comparative analysis, the structure OfCXCR4 appears well conserved at both the genomic DNA and the amino acid levels. Phylogenic analysis of OfCXCR4 revealed that the greatest homology was with its teleostean relatives. Expression studies showed ubiquitous OfCXCR4 transcription, mainly in immune organs, with the highest levels in the head kidney. Examination of OfCXCR4 transcriptional regulation post injection to different stimuli or pathogens revealed a significant modulation of mRNA expression as detected by reverse transcription-quantitative real-time PCR. Evidence of various transcription factor binding sites present in the 5′-flanking region of OfCXCR4 coupled with its observed regulated mRNA expression suggest that it may have an important role in immune surveillance in rock bream.