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，小肠的腔表面由专门的上皮组成，其适于通过存在大量绒毛、指状突起来增强营养吸收，所述绒毛、指状突起显著增加肠道中的表面积。绒毛的细胞只有3至4天的寿命，之后它们被起源于绒毛基部的细胞所取代，绒毛基部是上皮内陷内的干细胞龛。Wnt信号传导在调节这些干细胞的分化和增殖中起着重要作用，并且这些结构中的异常Wnt信号传导与胃肠道癌症密切相关。在绒毛形态发生开始时，肠管腔最初是光滑的，内胚层代表上皮干细胞的均匀池。绒毛形态发生通过管腔地形的显著变化进行，由此形成许多直的纵向脊，然后变成波浪形或扭结，最后绒毛开始在这些脊的拐点处形成。在这种转化结束时，干细胞群已被限制在将形成隐窝的绒毛间区域。这些转换产生的物理模式与压缩诱导的弹性材料的双向屈曲一致，这表明机械力可能计划在绒毛形态发生中发挥重要作用。因此，所提出的工作的目标是确定驱动中肠内胚层的地形变化的物理力量，以及这种独特的地形在肠绒毛图案化中起什么作用。假设在周围中胚层层中产生的物理力驱动内胚层中的压缩诱导的屈曲，并且这在形态发生梯度内置换内胚层细胞，提供引导分化成成熟绒毛的位置线索。提出了以下目标：具体目标1：确定主动力产生的作用，在形成和扭结的前绒毛纵脊。具体目标二：确定在整个绒毛形态发生阶段中中肠中胚层和内胚层中Wnts和相关基因的表达模式。具体目标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，小鸡是一个非常类似于人类胃肠道发育的模型系统，并将依赖于机械驱动的物理操作和遗传操作的组合，以确定发育中的组织如何利用物理力将细胞定位在空间变化的信号梯度内，以指定它们的成年形式。拟议的工作不仅可以推进我们的知识如何胃肠道癌症的形成和治疗，但可能有助于了解脊椎动物形态发生的基本机制，通过整合机械，分子和位置线索。

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.