The CD45 locus in cattle: allelic polymorphism and evidence for exceptional positive natural selection

Cattle in Africa are a genetically diverse population that has resulted fro m successive introduction of Asian Bos indicus and European B. taurus cattl e. However, analysis of mitochondrial genetic diversity in African cattle i dentified three lineages, one associated with Asian B. indicus, one with Eu ropean B. taurus, and a third ascribed to an indigenous African sub-species of cattle. Due to their extended co-evolution, indigenous African herbivor es are generally tolerant to endemic African pathogens. We are interested i n identifying alleles derived from the indigenous African cattle that may b e associated with tolerance to African pathogens. An analysis of the locus which encodes the abundant plasma membrane-associated tyrosine phosphatase, CD45, identified three highly divergent allelic families in Kenya Boran ca ttle. Analysis of allelic distribution in a diverse range of cattle populat ions suggests a European B. taurus, an Asian B, indicus, and an African ori gin. This demonstrates not only significant allelic polymorphism at the CD4 5 locus in cattle but also convincing autosomal evidence for a distinct Afr ican sub-species of cattle. Furthermore, maximum-likelihood analysis of sel ection pressures revealed that the CD45 locus is subject to exceptionally s trong natural selection which we suggest may be pathogen driven.