Basic characterization of avian β-defensin genes in the Japanese quail, Coturnix japonica.

In this study, we identified a cluster of 14 avian β-defensins (AvBD; approximately 66 kbp) in the Japanese quail, Coturnix japonica. Except for AvBD12 (CjAvBD12) and -13, the CjAvBDs coding sequences exhibited greater than 78.0% similarity to the respective orthologous chicken AvBD genes (GgAvBD). The putative amino acid sequence encoded by each CjAvBD contained six cysteine residues and the GXC (X1-2) motif considered essential for the β-defensin family. Each CjAvBDs also formed a sub-group with the respective orthologous genes of various bird species in a phylogenetic tree analysis. Synteny between the CjAvBD cluster and GgAvBD cluster was confirmed. The CjAvBD cluster was mapped on the long-arm end of chromosome 3 by linkage analysis based on single nucleotide polymorphisms (SNPs) of CjAvBD1 and CjAvBD12 (approximately 46 kbp), as well as GgAvBD cluster. We also confirmed that CjAvBD1, -4, -5, -9, and -10 are transcribed in 20 tissues, including immune and digestive tissues. However, our experimental data indicated that the CjAvBD cluster lacks the AvBD3 and -7 loci, whereas the CjAvBD101α, -101β, and -101θ loci arose from gene duplication of the AvBD6 orthologous locus in the CjAvBD cluster after differentiation between Coturnix - Gallus.