A new mechanism for a familiar mutation – bovine DGAT1 K232A modulates gene expression through multi-junction exon splice enhancement

<p>The <i>DGAT1</i> gene encodes an enzyme responsible for catalysing the terminal reaction in mammary triglyceride synthesis, and underpins a well-known pleiotropic quantitative trait locus (QTL) with a large influence on milk composition phenotypes. Since first described over 15 years ago, a protein-coding variant K232A has been assumed as the causative variant underlying these effects, following <i>in-vitro</i> studies that demonstrated differing levels of triglyceride synthesis between the two protein isoforms. In the current study, we used a large RNAseq dataset to re-examine the underlying mechanisms of this large milk production QTL, and hereby report novel expression-based functions of the chr14 g.1802265AA&gt;GC variant that encodes the <i>DGAT1 </i>K232A substitution. Using expression QTL (eQTL) mapping, we demonstrate a highly-significant mammary eQTL for <i>DGAT1, </i>where the K232A mutation appears as one of the top associated variants for this effect. By conducting <i>in vitro</i> expression and splicing experiments in bovine mammary cell culture, we further show modulation of splicing efficiency by this mutation, likely through disruption of an exon splice enhancer as a consequence of the allele encoding the 232A variant. Although the relative contributions of the enzymatic and transcription-based mechanisms now attributed to K232A remain unclear, these results suggest that transcriptional impacts contribute to the diversity of lactation effects observed at this locus.</p>