Keating Aileen F, Stanton Catherine, Murphy John J, Smith Terry J, Ross R Paul, Cairns Michael T
National Diagnostics Centre, National University of Ireland, Galway, Ireland.
Mamm Genome. 2005 Mar;16(3):184-93. doi: 10.1007/s00335-004-2325-0.
Conjugated linoleic acid (CLA) in milk arises through microbial biohydrogenation of dietary polyunsaturated fatty acids (PUFA) in the rumen, and by the action of mammary Stearoyl-CoA desaturase (Scd). A large variation (up to tenfold) in the concentration of this fatty acid in milk has been observed, even in cows receiving the same diet. The reasons for this variation are not well understood. In this study the bovine core promoter region was isolated by a genome walking strategy from genomic DNA Genome Walker libraries and then cloned and characterized. This core promoter sequence extended approximately 600 bp upstream of the translation start site. The presence of putative transcription factor binding sites conserved in bovine, human, and mouse promoters was observed. Evidence that this promoter fragment was functional in vivo was obtained from expression studies in a mammary cell line. The promoter sequence of the scd gene was compared between cows selected for the ability to produce high fatty acid methyl esters (FAME) (2.22-2.72) in their milk, with the same promoter region of low-FAME-producing cows (0.81-1.12). However, such comparisons of the sequences of the scd promoter region of cows producing high milk CLA compared with low CLA revealed no polymorphisms in this promoter segment. Furthermore, no sequence polymorphisms were observed among the scd promoter region of Holstein Friesian, Montbeliarde, Normande, Norwegian Red, Charlois, Limousin and Kerry breeds.
牛奶中的共轭亚油酸（CLA）是通过瘤胃中膳食多不饱和脂肪酸（PUFA）的微生物生物氢化作用以及乳腺硬脂酰辅酶A去饱和酶（Scd）的作用产生的。即使是接受相同日粮的奶牛，其牛奶中这种脂肪酸的浓度也存在很大差异（高达十倍）。这种差异的原因尚不清楚。在本研究中，通过基因组步移策略从基因组DNA基因组步移文库中分离出牛核心启动子区域，然后进行克隆和表征。该核心启动子序列在翻译起始位点上游延伸约600 bp。观察到在牛、人和小鼠启动子中保守的假定转录因子结合位点的存在。从乳腺细胞系的表达研究中获得了该启动子片段在体内具有功能的证据。比较了在牛奶中能够产生高脂肪酸甲酯（FAME）（2.22 - 2.72）的奶牛与低FAME产生奶牛（0.81 - 1.12）相同启动子区域的scd基因启动子序列。然而，比较高牛奶CLA产量奶牛与低CLA产量奶牛的scd启动子区域序列，在该启动子片段中未发现多态性。此外，在荷斯坦弗里生、蒙贝利亚尔、诺曼底、挪威红牛、夏洛来、利木赞和凯里品种的scd启动子区域之间未观察到序列多态性。
