Mechanical and molecular factors underlying morphogenesis of the intestinal villi

描述(申请人提供)：在高等脊椎动物中，小肠的管腔表面由专门的上皮组成，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中绒毛底部的细胞所取代，这些细胞是上皮凹陷中的干细胞壁龛。Wnt信号在这些干细胞的分化和增殖过程中起着重要的调节作用，而这些结构中异常的Wnt信号与胃肠道肿瘤的发生密切相关。在绒毛形态发生开始时，肠管管腔最初是光滑的，内内胚层代表一个统一的上皮干细胞池。绒毛的形态发生在管腔地貌中经历了显著的变化，形成了许多直的纵脊，然后变成波浪状或缠绕，最后在这些脊的拐点处开始形成绒毛。在这种转变结束时，干细胞群体已经限制在绒毛间区域，在那里将形成隐窝。这些转变产生的物理模式与压缩诱导的弹性材料双向屈曲一致，这表明机械力可能在绒毛形态发生中扮演重要角色。因此，这项拟议工作的目标是确定驱动中肠内胚层地形变化的物理力，以及这一独特的地形在形成肠道绒毛模式方面所起的作用。假设是在周围的中胚层中产生的物理力驱动内胚层受压缩诱导的屈曲，这会取代形态原梯度内的内胚层细胞，提供引导分化为成熟绒毛的位置线索。提出了以下目标：具体目标1：确定主动力产生在绒毛前纵脊的形成和扭结中的作用。特定目的2：确定WNTS及其相关基因在绒毛形态发生过程中中肠、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皮细胞形态的依赖性。这些研究将在雏鸡身上进行，这是一个非常类似人类胃肠道发育的模型系统，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量将细胞定位在空间变化的信号梯度中，以确定它们的成年形态。这项拟议的工作不仅可能促进我们对胃肠道癌症如何形成和可以治疗的了解，而且可能有助于理解脊椎动物通过机械、分子和位置线索的整合进行形态发生的基本机制。

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.