Genomic Organization and Expression of the Bovine NK-Lysin Gene Family

Human granulysin and its pig ortholog, NK-lysin, are antimicrobial peptides (AMPs) which play important roles in the host immune response against invading pathogens. AMPs are active against a wide spectrum of microorganisms including bacteria, fungi, protozoa, viruses and even cancerous cells. NK-lysin orthologs have been discovered and characterized in other species, including chicken, cattle, water buffalo and horse. Orthologs have been sought but not found in mouse or other rodents. While the functions of the NK-lysin peptides have been relatively well studied, the genomic organization and variation in the genes has received much less attention.

This study focused on the genomic organization and variation of the bovine NK-lysin gene family. Single molecule real time sequencing (SMRT) data from two BAC clones identified four NK-lysin genes NK1, NK2, NK3 and NK4 in the cattle genome. These genes are contiguous on chromosome 11 and may have arisen from a single gene by tandem duplication. NK-lysin orthologs in other animals have been reported as single genes. While bovine NK1, NK2 and NK3 share high identity for both their genomic size and sequence, NK4 is diverged from the other three genes. We showed distinct expression profiles for each gene in five different collected tissues. Furthermore, expression levels for each gene in bronchial lymph nodes from RNA-seq data were compared in non-challenged animals (N=3) and six experimental groups (each N = 4) of Angus × Hereford animals that had been artificially challenged with Mycoplasma spp, Pasteurella multocida, Mannheimia haemolytica, Bovine respiratory syncytial virus, Bovine viral diarrhea and Infectious bovine rhinotracheitis. Expression of NK1, NK2 and NK3 genes was elevated in most of the challenged animals while NK4 was not (p ≤ 0.05). In conclusion, we report that the single granulysin (NK-lysin) gene of humans and pig is expanded to a four gene family in the cattle genome and expression profiles differ among the four genes.