Mechanical and molecular factors underlying morphogenesis of the intestinal villi

描述（由申请人提供）：在高等脊椎动物中，小肠的管腔表面由一个专门的上皮组成，通过大量绒毛的存在来增强营养吸收，手指状突起显著增加肠道的表面积。绒毛细胞的寿命只有3到4天，之后它们被起源于隐窝绒毛基部的细胞所取代，隐窝是上皮内陷内的干细胞壁龛。Wnt信号在调节这些干细胞的分化和增殖中起着重要作用，这些结构中异常的Wnt信号与胃肠道癌症密切相关。绒毛形态发生时，肠管腔最初是光滑的，内胚层为均匀的上皮干细胞池。绒毛的形态发生是通过管腔地形的显著变化进行的，由此形成一些直的纵向脊，然后变成波浪状或扭结，最后绒毛开始在这些脊的拐点上形成。在这种转化结束时，干细胞群已经被限制在绒毛间区域，在那里将形成隐窝。这些转变产生的物理模式与弹性材料的压缩诱导的双向屈曲一致，表明机械力可能在绒毛形态发生中起重要作用。因此，本研究的目的是确定驱动中肠内胚层地形变化的物理力量，以及这种独特的地形在肠绒毛的形成中所起的作用。据推测，在中胚层周围产生的物理力驱动了内胚层的压缩引起的屈曲，并且这种屈曲使内胚层细胞在形态梯度内移位，提供了引导分化为成熟绒毛的位置线索。具体目标1：确定在绒毛前纵脊的形成和扭结中主动力产生的作用。特异性目的2：确定绒毛形态发生过程中wnt及相关基因在中肠中、中胚层和内胚层的表达模式。具体目的3：确定绒毛形态发生对内胚层地形的依赖性。这些研究将在小鸡中进行，这是一个与人类胃肠道发育非常相似的模型系统，将依赖于机械驱动的物理操作和遗传操作的结合，以确定发育中的组织如何利用物理力量在空间变化的信号梯度中局部定位细胞，以指定它们的成年形式。这项工作不仅可以提高我们对胃肠道癌症形成和治疗的认识，而且可以帮助我们理解脊椎动物形态发生的基本机制，通过机械、分子和位置线索的整合进行。

DESCRIPTION (provided by applicant): In higher vertebrates, the luminal surface of the small intestine consists of a specialized epithelium adapted to enhance nutrient absorption through the presence of numerous villi, finger-like projections that dramatically increase surface area in the gut. Cells of the villus have a lifetime of only 3 to 4 days, after which they are replaced by cells originating at the villus base in crypts, stem cell niches within invaginations of the epithelium. Wnt signaling plays an important role in regulating the differentiation and proliferation of these stem cells, and abnormal Wnt-signaling in these structures has been strongly associated with gastrointestinal cancers. At the onset of villi morphogenesis, the gut tube lumen is initially smooth, and the inner endodermal layer represents a uniform pool of epithelial stem cells. Villi morphogenesis proceeds through striking transformations in luminal topography, whereby a number of straight longitudinal ridges form, then become wavy, or kinked, and finally villi begin to form at the points of inflection in these ridges. By the end of this transformation, stem cell populations have become restricted to intervillus regions where the crypts will form. These transformations generate physical patterns consistent with compression induced bi-directional buckling of an elastic material, suggesting that mechanical forces may plan an important role in villi morphogenesis. Therefore, the objective of the proposed work is to determine the physical forces that drive topographical changes of the midgut endoderm, and what role this unique topography plays in patterning the intestinal villi. It is hypothesized that physical forces generated in the surrounding mesodermal layers drive compression- induced buckling in the endoderm, and that this displaces endodermal cells within a morphogen gradient, providing positional cues that guide differentiation into mature villi. The following aims are proposed: Specific Aim 1: Determine the role of active force generation in the formation and kinking of pre-villus longitudinal ridges. Specific Aim 2: Determine the expression pattern of Wnts and related genes in the midgut mesoderm and endoderm throughout the stages of villus morphogenesis. Specific Aim 3: Determine the dependence of villus morphogenesis on endodermal topography. These investigations will be carried out in the chick, a model system that closely resembles human gastrointestinal development, and will rely on a combination of mechanically motivated physical manipulations and genetic ones to identify how developing tissues may exploit physical forces to position cells locally within spatially varying signaling gradients in order to specify their adult form. The proposed work may not only advance our knowledge of how gastrointestinal cancers form and can be treated, but may aid in understanding the fundamental mechanisms by which vertebrate morphogenesis proceeds through an integration of mechanical, molecular, and positional cues. PUBLIC HEALTH RELEVANCE: In humans and other higher vertebrates, the cells that form the lining of the adult intestine are organized into many finger-like projections, termed villi, that are essential for nutrient absorption. These cells live for only days before they are replaced by new cells that originate in a special compartment of stem cells, known as crypts. Unfortunately, if these villi do not form normally during embryonic development, the intestine cannot perform its function, and if during adulthood, the signals that sustain this cycle of stem cell differentiation become perturbed, lethal cancers can form in the small intestine and colon. Because during embryonic development, the cells that create these crypts and villi are initially stem-cell like, understanding how the villi form, and how stem cells become regulated and restricted to the crypts during development will help determine how gastrointestinal cancers form and may reveal targets for their treatment. The objective of the proposed work is to determine the physical forces and molecular pathways responsible for the development of intestinal villi.