Cell: Cell Interactions During Late Intestinal Development

描述(申请人提供)：小肠上皮被组织成瓶状腺(隐窝)，其中含有肠道干细胞和被分化细胞覆盖的指状突起(绒毛)。沿着极化的隐窝到绒毛轴，建立了一个持续的细胞分裂、分化和迁移过程。这一垂直轴的建立和维持需要细胞：细胞在上皮和下层间充质之间的串扰，这对肠道的正常内稳态至关重要。对新建立的Hhedgehog(HH)信号被阻断的小鼠模型(HHIP转基因小鼠)的分析表明，隐窝/绒毛轴的建立需要这一信号通路。HH信号从上皮细胞发出，由间充质细胞接收。Shh和IHH参与这一信号；这两个信号蛋白既有重叠的作用，也有不同的作用。失去结合的HH信号可以在绒毛顶端形成异位的隐窝前结构，从而扰乱隐窝/绒毛轴的正常组织。HHIP小鼠的上皮表型反映了细胞的变化：上皮细胞和上皮下肌成纤维细胞的扩大群体之间的细胞串扰。该方案验证了以下假设：来自上皮细胞的IHH和Shh信号由上皮下肌成纤维细胞接收，并间接地限制和组织Wnt反应的上皮腺前间隙。在目标1中，将比较野生型、Shh-/-、IHH-/-和HHIP小鼠在肠道发育后期伴随隐窝/绒毛轴极化的分子和形态事件的序列。在目标2中，将确定间充质室内HH信号的靶点。将寻找Shh和IHH的单独和共同靶点；将测试HH在不同浓度下诱导不同基因的可能性。最后，目标3探索了HH蛋白如何发挥作用来组织隐窝/绒毛轴(即通过形态梯度极化或通过锚定隐窝前区域)，并测试特定候选基因在形成这一轴模式中的作用。这项工作将提供对细胞的新见解：对肠道发育至关重要的细胞信号通路。

DESCRIPTION (provided by applicant): The small intestinal epithelium is organized into flask-like glands (crypts) that contain intestinal stem cells and finger-like projections (villi) covered by differentiated cells. A constant process of cell division, differentiation and migration is established along a polarized crypt to villus axis. Establishment and maintenance of this vertical axis requires cell:cell crosstalk between the epithelium and the underlying mesenchyme and is critical to proper homeostasis of the intestine. Analysis of a newly established mouse model in which hedgehog (Hh) signals are blocked (Hhip transgenic mice) reveals that establishment of the crypt/villus axis requires this signaling pathway. Hh signals emanate from the epithelium and are received by the mesenchyme. Shh and Ihh participate in this signal; these two signaling proteins have both overlapping and separate roles. Loss of the combined Hh signal permits the formation of ectopic pre-crypt structures on villus tips, thus disrupting the normal organization of the crypt/villus axis. The epithelial phenotype of Hhip mice reflects alterations in cell:cell crosstalk between the epithelial cells and an expanded population of subepithelial myofibroblasts. The proposal tests the following Hypothesis: A combined Ihh and Shh signal from the epithelium is received by subepithelial myofibroblasts and acts indirectly to limit and organize the Wnt responsive epithelial pre-crypt compartment. In Aim 1, the sequence of molecular and morphological events that accompany crypt/villus axis polarization during late intestinal development will be compared in wild type, Shh -/-, Ihh -/- and Hhip mice. In Aim 2, the targets of Hh signaling in the mesenchymal compartment will be identified. Separate and common targets of Shh and Ihh will be sought; the possibility that Hh induces different genes at different concentrations will be tested. Finally, Aim 3 explores how Hh proteins function to organize the crypt/villus axis (i.e., by polarization via a morphogen gradient or by anchoring of the pre-crypt region) and tests specific candidate genes for their role in patterning this axis. The work will provide new insights into cell:cell signaling pathways crucial for intestinal development.