CDX EXPRESSION IN THE GASTROINTESTINAL TRACT

指导胃肠道器官特异性分化的分子机制尚不清楚。包括转录因子在内的多种因素的复杂相互作用是肠胃分化发育所必需的。Cdx1和Cdx2是肠道特异性同源盒转录因子，是指导肠道发育、分化和维持肠道表型的候选基因。CDX1虽然不在正常胃中表达，但在胃粘膜的肠化生中表达，提示在这一病理过程中起作用。本课题的目的是通过两种体内模型，通过Cdx蛋白的条件表达，确定Cdx1和Cdx2在胚胎发生早期对未分化内胚层和分化小肠和胃中的表达的影响。为了检测Cdx在早期胚胎发育中的表达，我们将Cdx1和Cdx2的编码区置于Hnf3gamma启动子的控制之下。在转基因小鼠中，Hnf3gamma/Cdx构建体将指导Cdx在发育中的肠内胚层的过早表达和Cdx在发育中的胃的异位表达。将分析转基因小鼠在胚胎发生过程中肠和胃的形态学变化。此外，将通过原位杂交和免疫组织化学分析胃，以确定Cdx1或Cdx2的表达是否会改变胃粘膜的正常分化，或诱导肠道特异性基因的表达。我们将构建第二组转基因动物，研究Cdx表达对分化的胃肠道黏膜的影响。Cdx1和Cdx2的表达将受到Cdx条件表达的四环素诱导启动子的控制。我们将对这些动物进行分析，以确定Cdx表达对肠上皮细胞增殖和形态的影响，以及对胃中肠道特异性基因形态和表达的影响。后者可作为胃粘膜肠化生中Cdx表达的模型。本实验旨在阐明肠特异性转录因子Cdx1和Cdx2在早期胚胎发生或断奶动物肠胃分化中的作用，以进一步了解肠胃分化和器官特异性维持的一些基本机制。

The molecular mechanisms directing organ specific differentiation in the gastrointestinal tract are unknown. Complex interactions of multiple elements, including transcription factors, are necessary for the differentiation and development of the intestine and stomach. Cdx1 and Cdx2, intestine specific homeobox transcription factors, are candidate genes for directing intestinal development, differentiation and the maintenance of the intestinal phenotype. CDX1, though not in the normal stomach, is expressed in intestinal metaplasia of the gastric mucosa, suggesting a role in this pathologic process. The goal of this proposal is to determine, through two in vivo models the effect of Cdx1 and Cdx2 expression first, in early embryogenesis on undifferentiated endoderm and second, in differentiated intestine and stomach by conditional expression of the Cdx proteins. To examine Cdx expression in early embryogenesis, the coding region of Cdx1 and Cdx2 will be placed under the control of the Hnf3gamma promoter. In transgenic mice the Hnf3gamma/Cdx construct will direct premature expression of Cdx in the endoderm of the developing intestine and ectopic expression of Cdx in the developing stomach. The transgenic mice will be analyzed for morphologic changes in the intestine and stomach throughout embryogenesis. In addition, the stomach will be analyzed by in situ hybridization and immunohistochemistry to determine if Cdx1 or Cdx2 expression can alter the normal differentiation of the gastric mucosa, or induce the expression of intestine specific genes. A second set of transgenic animals will be constructed to study the effect of Cdx expression on differentiated gastric and intestinal mucosa. Expression of Cdx1 and Cdx2 will be under the control of a tetracycline inducible promoter for conditional expression of Cdx. These animals will be analyzed to determine the effect of Cdx expression on the proliferation and morphology of the intestinal epithelium and on the morphology and expression of intestinal specific genes in the stomach. The later will serve as a model for Cdx expression found in intestinal metaplasia of the gastric mucosa. These experiments are designed to elucidate the function of the intestine specific transcription factors Cdx1 and Cdx2 on the differentiation of the intestine and stomach in early embryogenesis or in weaned animals in order to further our understanding of some of the basic mechanisms involved in intestinal and gastric differentiation and the maintenance of organ specificity.