Putative intestine-specific enhancers located in 5′ sequence of the CDX1 gene regulate CDX1 expression in the intestine

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.