Rankin Erinn B, Xu Wei, Silberg Debra G, Suh EunRan
Gastroenterology Div., Dept. of Medicine, Univ. of Pennsylvania, Ste. 600, 415 Curie Blvd., Philadelphia, PA 19104, USA.
Am J Physiol Gastrointest Liver Physiol. 2004 May;286(5):G872-80. doi: 10.1152/ajpgi.00326.2003. Epub 2004 Jan 8.
CDX1 is a homeobox transcription factor that plays a critical role in intestinal epithelial cell growth and differentiation. CDX1 gene expression is tightly regulated in a temporal and cell-type specific manner. However, very little is known about the regulatory mechanisms that direct CDX1 gene expression in the intestine. To elucidate these mechanisms, we employed a series of transgenic mouse studies using the 5' flanking sequences of the human CDX1 gene. Transgenic mice containing nucleotides between -5667 and +68 relative to the transcription start site of the CDX1 gene demonstrated ectopic expression of the transgene in the brain and gastric smooth muscle. However, transgenic expression of the nucleotides -15601 to +68 of the CDX1 gene was restricted to the intestinal epithelium, which was identical to endogenous CDX1 gene expression. Taken together, the upstream sequences between -15601 and -5667 contain regulatory elements that direct transgene expression specifically to the intestinal epithelium. Furthermore, DNase I hypersensitivity assays revealed two active chromatin regions in the CDX1 gene (hypertensive sites 1 and 2) located at approximately -5.8 and -6.8 kb upstream of the CDX1 gene, respectively, which may function as potential intestine-specific enhancers.
CDX1是一种同源框转录因子，在肠道上皮细胞的生长和分化中起关键作用。CDX1基因的表达以时间和细胞类型特异性的方式受到严格调控。然而，关于在肠道中指导CDX1基因表达的调控机制，我们知之甚少。为了阐明这些机制，我们利用人CDX1基因的5'侧翼序列进行了一系列转基因小鼠研究。相对于CDX1基因转录起始位点，包含-5667至+68核苷酸的转基因小鼠在大脑和胃平滑肌中显示出转基因的异位表达。然而，CDX1基因-15601至+68核苷酸的转基因表达仅限于肠道上皮，这与内源性CDX1基因的表达相同。综上所述，-15601至-5667之间的上游序列包含将转基因表达特异性导向肠道上皮的调控元件。此外，DNA酶I超敏分析揭示了CDX1基因中的两个活性染色质区域（高敏位点1和2），分别位于CDX1基因上游约-5.8和-6.8 kb处，它们可能作为潜在的肠道特异性增强子发挥作用。
