Characterization and expression of non-polymorphic liver expressed antimicrobial peptide 2: LEAP-2 in the Japanese quail, Coturnix japonica.

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a cationic peptide that plays an important role in innate immunity for host defense. The aim of this study was to characterize the LEAP-2 gene in the Japanese quail (Coturnix japonica). Japanese quail LEAP-2 (CjLEAP-2) was identified from the Japanese quail draft genome database by a local BLAST analysis using chicken LEAP-2 (GgLEAP-2). The exon-intron structure of CjLEAP-2, analyzed from three quails, is composed of three exons, as is the chicken LEAP-2 homolog (GgLEAP-2). An analysis of the coding sequence revealed that CjLEAP-2 is 231 bp long, like GgLEAP-2, and 93% identical to GgLEAP-2 at the nucleic acid level. The predicted amino acid sequence of CjLEAP-2 contained the liver-expressed antimicrobial peptide 2-precursor domain and four cysteine residues characteristic of the LEAP-2 protein. The amino acid sequence of the mature peptide of CjLEAP-2 was 100% identical to that of GgLEAP-2. We confirmed that CjLEAP-2 was transcribed in at least seven tissues, including the digestive system. Additionally, the mature peptide region of CjLEAP-2 exhibited no polymorphisms in 99 quails from six strains. Taken together, these findings indicate that CjLEAP-2 is non-polymorphic and therefore, it likely plays an important role in the innate immunity of quail as it does in chicken.