The DGAT1 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 in-vitro studies that demonstrated differing levels of triglyceride synthesis between the two protein isoforms. 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 > GC variant that encodes the DGAT1 K232A substitution. Using expression QTL (eQTL) mapping, we demonstrate a highly-significant mammary eQTL for DGAT1, where the K232A mutation appears as one of the top associated variants for this effect. By conducting in vitro 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. The relative contributions of the enzymatic and transcription-based mechanisms now attributed to K232A remain unclear; however, these results suggest that transcriptional impacts contribute to the diversity of lactation effects observed at the DGAT1 locus.

中文翻译：

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熟悉的突变的新机制-牛DGAT1 K232A通过多结外显子剪接增强来调节基因表达。

DGAT1基因编码一种酶，该酶负责催化乳腺甘油三酸酯合成中的末端反应，并支撑着众所周知的多效性定量性状基因座（QTL），对牛奶成分表型影响很大。自15年前首次描述以来，在体外研究表明两种蛋白质同工型之间甘油三酯合成水平不同后，一直认为蛋白质编码变异K232A是引起这些效应的原因。我们使用了一个大型RNAseq数据集来重新检查这种大型牛奶产量QTL的潜在机制，并据此报告了编码DGAT1 K232A替代的chr14 g.1802265AA> GC变体的新型基于表达的功能。使用表达QTL（eQTL）映射，我们展示了DGAT1的高度重要的乳腺eQTL，其中K232A突变是该效应的最相关变异之一。通过在牛乳腺细胞培养物中进行体外表达和剪接实验，我们进一步显示了这种突变对剪接效率的调节，这可能是由于编码232A变异的等位基因导致外显子剪接增强子的破坏。目前尚不清楚归因于K232A的基于酶和转录的机制的相对贡献；但是，这些结果表明，转录影响有助于在DGAT1基因座处观察到的泌乳作用的多样性。这可能是由于等位基因编码232A变体导致外显子剪接增强子受阻。目前尚不清楚归因于K232A的基于酶和转录的机制的相对贡献；但是，这些结果表明，转录影响有助于在DGAT1基因座处观察到的泌乳作用的多样性。可能是由于等位基因编码232A变体导致外显子剪接增强子被破坏。目前尚不清楚归因于K232A的基于酶和转录的机制的相对贡献；但是，这些结果表明，转录影响有助于在DGAT1基因座处观察到的泌乳作用的多样性。