Discovery of Convergent Adaptations that Alleviate Heat Stress in Taurine Cattle

The slick hair coat locus (SLICK) contains a dominantly inherited trait typically associated with tropically adapted, Criollo-derived cattle breeds.  The trait is associated with a less dense and shorter hair coat that confers an ability to better endure heat stress.  Such an adaptive trait is of interest in tropical cattle rearing regions, because it has been associated with sustained levels of growth or milk production in comparison to most other taurine breeds without this trait.  To identify mutations underlying SLICK, we surveyed whole genome resequencing data from 21 slick and normal hair animals within the GWAS-determined candidate region on chromosome 20 (BTA20) from 37.5-39.5 Mbp.  The resultant sequence variants were annotated, and the only likely causative variants were a one base deletion causing a frameshift within the coding region of prolactin receptor (PRLR) and a stop-gain mutation within the same gene.  Both mutations are contained in the last exon of PRLR and both truncate the long form of the encoded protein; thereby removing tyrosine residues vital for JAK2/STAT5 signaling.  Validation testing of these two sequence variants along with 94 other candidate SNP across a DNA panel (N=911 animals) made up of different breeds from the U.S., Nigeria, and Brazil, as well as 13 Criollo influenced populations from across the Americas and Australia strongly supported the frameshift mutation in PRLR as the causative mutation underlying SLICK in Senepol and some Romosinuano cattle, while the stop-gain mutation was specific to Criollo breeds from Venezuela.  To better understand how these SLICK mutations reduce the impact of heat stress on production, the effects of these two adaptive neomutations are being analyzed RNAseq analysis of normal and mutant hair bulbs and also validated by genome-editing in model animal species.