Identify and characterize novel Wnt pathway genes

描述(申请人提供)：脊椎动物中胚层的形成是一个高度复杂和不变的过程。在脊椎动物的肢体中，在胚胎发育期间必须指定40多块肌肉。人们对肌肉形成的分子因素和途径知之甚少。最近，PI发现了Wnt信号通路在脊椎动物肢体肌肉模式中的作用。令人惊讶的是，Wnt途径并不是发育中的肌肉所必需的，而是在发育中的肌肉周围的一群细胞中需要的。Wnt通路活跃的细胞群体创造了一种肌肉“前置模式”。通过一种未知的机制，迁移的成肌细胞似乎感觉到了含有活跃的Wnt途径的细胞产生的前模式，并开始分化。Wnt信号通路最下游的成分是Tcf/Lef类转录因子。在小鼠和小鸡的肢体中，PI显示TCF4在分化肌肉(“肌周”)周围的一群细胞中表达。在鸡的肌肉周围区域错误表达显性-阴性版本的TCF4会导致肌肉形成异常和肢体畸形。有许多已确定的TCF4下游靶点(以及一般的Wnt信号)，但这些因素似乎都不参与肌肉模式的形成。在鼠标系统中进行大规模筛选以识别与肌肉构图有关的Wnt信号靶标将是昂贵和耗时的。雏鸟系统中缺乏基因，这使得这种类型的筛查变得不可能。然而，线虫非常适合用于遗传和分子筛选。线虫含有单一的TCF4同源物POP-1。PI显示，POP-1突变的动物在中胚层模式方面存在缺陷，他们建议使用这种表型作为筛选的基础，以识别与Wnt信号有关的其他基因。这一筛选有可能识别作为Wnt途径的直接靶点的基因，与Wnt途径平行工作的基因，或者功能独立于Wnt途径而形成中胚层组织的基因。建议的筛选是唯一适合于确定脊椎动物和无脊椎动物的肌肉规格和Wnt信号中涉及的新因素。一旦确定了候选基因，PI将使用鸡和小鼠系统来验证这些因素在形成脊椎动物中胚层组织模式中的作用。PI具有使用线虫、小鼠和小鸡模型系统的经验，并处于充分利用每个系统的位置。

DESCRIPTION (provided by applicant): Vertebrate mesodermal formation is a highly intricate and invariant process. In the vertebrate limb over 40 muscles must be specified during embryonic development. Very little is known about the molecular factors and pathways responsible for muscle formation. Recently, the PIs have uncovered a role for the Wnt signaling pathway in muscle patterning in the vertebrate limb. Surprisingly, the Wnt pathway is not required within developing muscles, but in a population of cells that surround the developing muscles. The cell population in which the Wnt pathway is active creates a muscle "pre-pattern". Through an unknown mechanism, migrating myoblasts appear to sense the pre-pattern produced by cells containing an active Wnt pathway and begin to differentiate. The most downstream components of the Wnt signaling pathway are the Tcf/Lef class of transcription factors. In the mouse and chick limb the PIs have shown that Tcf4 is expressed in a population of cells that surrounds differentiating muscles ("perimuscular"). Misexpressing a dominant-negative version of TCF4 in the chick perimuscular region resulted in abnormal muscle formation and a malformed limb. There are a number of identified downstream targets of TCF4 (and Wnt signaling in general) but none of these factors appear to be involved in muscle patterning. It would be expensive and time consuming to perform large-scale screens in the mouse system to identify Wnt signaling targets involved in muscle patterning. The lack of genetics in the chick system makes this type of screen impossible. However, the nematode C. elegans is ideally suited for genetic and molecular screens. C. elegans contains a single TCF4 homologue, POP-1. The PIs show that animals with a mutation in pop-1 have defects in mesodermal patterning and they propose to use this phenotype as the basis for a screen to identify additional genes involved in Wnt signaling. This screen has the potential to identify genes that are direct targets of the Wnt pathway, that work in parallel pathways along with the Wnt pathway, or that function independently of the Wnt pathway to pattern mesodermal tissues. The proposed screen is uniquely suited to identify new factors involved in muscle specification and Wnt signaling in both vertebrates and invertebrates. Once candidate genes have been identified the PIs will then use the chick and mouse systems to validate the roles of these factors in patterning vertebrate mesodermal tissues. The PIs have experience working with C. elegans, mice and chick model systems and are positioned to take full advantage of each system.