Transcriptome provides insights into bovine mammary regulatory mechanisms during the lactation cycle

The molecular events underlying the lactation curve of dairy animals have long been a biological conundrum for mammary biologists, and a cause of a considerable loss of income for dairy farmers. To better understand the regulatory mechanisms and developmental processes of the mammary gland during the lactation cycle, whole-genome transcriptome profiles of bovine mammary tissues at five different lactation stages were investigated using the RNA-Seq technique. The differentially expressed genes were identified by comparing different lactation stage combinations. Gene expression changes were validated using quantitative reverse-transcription polymerase chain reaction. Some differentially expressed genes were found to locate in the known quantitative trait loci regions that are associated with multiple milk production traits. Proteins of potentially important genes were confirmed to be expressed in the mammary epithelium of dairy cows. An integrated analysis of differential gene expression indicated that internal development regularities underlying the shape of the milk production curve. First, the mammary gland is enriched in similar activities during lactation onset and involution, but in opposite regulatory directions. Second, the lactation stages before and after the milk peak shared similar biological processes that were mainly involved in extracellular matrix remodelling. The discoveries of the study provide information necessary to improve milk production.

长期以来，乳用动物泌乳曲线背后的分子事件一直是乳腺生物学家面临的生物学难题，同时也给奶农造成了可观的经济损失。为深入解析泌乳周期中乳腺的调控机制与发育过程，本研究采用RNA测序（RNA-Seq）技术，对5个不同泌乳阶段的奶牛乳腺组织开展了全基因组转录组分析。通过对比不同泌乳阶段的组合样本，筛选得到差异表达基因（differentially expressed genes, DEGs），并采用定量反转录聚合酶链反应（quantitative reverse-transcription polymerase chain reaction, qRT-PCR）对基因表达变化进行了验证。部分差异表达基因定位于已知的与多种产奶性状相关的数量性状基因座（quantitative trait loci, QTL）区域内。研究证实，部分潜在关键基因编码的蛋白可在奶牛乳腺上皮细胞中表达。对差异基因表达的整合分析揭示了泌乳曲线形态背后的内在发育规律：其一，乳腺在泌乳启动与退化阶段的生物学活动类型相似，但调控方向完全相反；其二，泌乳峰值前后的阶段共享相似的生物学过程，主要涉及细胞外基质重塑（extracellular matrix remodelling）。本研究的发现为提升产奶量提供了必要的理论依据与数据支撑。