Two Lineages of with Contrasting Transcription Patterns Have Been Conserved at a Single Locus during Ruminant Speciation.

Cattle possess the most diverse repertoire of NK cell receptor genes among all mammals studied to date. Killer cell receptor genes encoded within the NK complex and killer cell Ig-like receptor genes encoded within the leukocyte receptor complex have both been expanded and diversified. Our previous studies identified two divergent and polymorphic alleles within the NK complex in the Holstein-Friesian breed of dairy cattle. By examining a much larger cohort and other ruminant species, we demonstrate the emergence and fixation of two allele lineages ( and -) at a single locus during ruminant speciation. Subsequent recombination events between these allele lineages have increased the frequency of extracellular domains. and transcription levels contrasted in response to cytokine stimulation, whereas homozygous animals consistently transcribed higher levels of , regardless of the allele lineage. mRNA levels were also generally higher than Collectively, these data point toward alternative functional roles governed by genotype and allele lineage. On a background of high genetic diversity of NK cell receptor genes, this allele fixation points to fundamental and potentially differential function roles.