The role of cell polarity in vertebrate limb outgrowth

描述(申请人提供)：肢体畸形是一些最常见的出生缺陷，大约发生在每1000人出生中就有0.7到1例。因此，了解四肢正常生长和形成模式的机制是医学界非常感兴趣的。研究人员的长期目标是了解驱动肢体生长和形态发生的细胞和分子机制。这项应用专门研究成纤维细胞生长因子(FGFs)和Wnt/平面细胞极性(PCP)信号在确定肢体间充质细胞肌动蛋白细胞骨架和有丝分裂纺锤体的极性作为肢体突起的基础机制中所起的作用。 一段时间以来，人们已经知道，脊椎动物胚胎肢芽的远端边缘存在着一小段外胚层组织，这是邻近肢体间充质生长所必需的。最近的研究表明，分泌型成纤维细胞生长因子家族的成员在这种组织(称为顶端外胚层脊或AER)中表达，是肢体间充质生长的必要条件和充分条件。虽然FGFs调节生长的机制尚不清楚，但最近的数据表明，它们是通过作为肢体间充质的化学吸引剂而不是作为有丝分裂或细胞生存因子来实现的。成纤维细胞生长因子信号是如何调节这种化学吸引的？研究人员收集的初步数据表明，AER信号激活了肢体间充质中分泌的Wnt配体Wnt5a的表达。在鱼类和两栖动物模型中，Wnt5a已被证明通过Wnt/平面细胞极性(PCP)途径发出信号。WNT/PCP信号在细胞极性的建立中起着关键作用，细胞极性是原肠发育过程中细胞定向运动和细胞分裂的基础，对延长胚轴是必不可少的。他假设，来自AER的成纤维细胞生长因子信号在肢体间充质中建立了Wnt5a表达的梯度，然后在这些细胞中建立了极性，进而引导近端细胞运动和/或细胞分裂，从而导致肢体突起。在这一应用中，研究人员将检验这一假设，即成纤维细胞生长因子和Wnt/PCP信号对于肌动蛋白细胞骨架或有丝分裂纺锤体的极化是必要和充分的。此外，他还将研究成纤维细胞生长因子和Wnt/PCP信号在调节细胞极性方面的上位关系。

DESCRIPTION (provided by applicant): Limb anomalies represent some of the most common birth defects, occurring in approximately 0.7 to 1 per 1,000 human births. Therefore, understanding the mechanisms responsible for the proper outgrowth and patterning of limbs are of great interest to the medical community. The investigator's long term objective is to understand the cellular and molecular mechanisms that drive outgrowth and morphogenesis of the limb. This application specifically examines the role of fibroblast growth factors (FGFs) and Wnt/planar cell polarity (PCP) signaling in establishing polarity of the actin cytoskeleton and mitotic spindle of limb mesenchyme cells as mechanisms that underlie limb outgrowth. For some time it has been known that a small ridge of ectodermal tissue that exists along the distal margin of the vertebrate embryonic limb bud is required for outgrowth of the adjacent limb mesenchyme. More recently, it has been demonstrated that members of the secreted fibroblast growth factor (FGF) family are expressed in this tissue (known as the apical ectodermal ridge or AER) and are both necessary and sufficient for outgrowth of the limb mesenchyme. While the mechanisms by which FGFs mediate outgrowth are unknown, recent data suggest that they do so by acting as a chemoattractant to the limb mesenchyme rather than as a mitogenic or cell survival factor. How does FGF signaling mediate this chemoattraction? The investigator has collected preliminary data suggesting that AER signals activate the expression of the secreted Wnt ligand, Wnt5a in the limb mesenchyme. In fish and amphibian models, Wnt5a has previously been demonstrated to signal through the Wnt/planar cell polarity (PCP) pathway. Wnt/PCP signaling plays a critical role in establishing cellular polarity which underlies directional cell movements and cell divisions during gastrulation, essential for elongating the embryonic axis. He hypothesizes that Fgf signaling from the AER establishes a gradient of Wnt5a expression in the limb mesenchyme, which then establishes polarity in these cells and in turn directs proximal to distal cell movements and/or cell divisions that result in limb outgrowth. In this application the investigator will test the hypothesis that Fgf and Wnt/PCP signaling are necessary and sufficient for polarization of the actin cytoskeleton or the mitotic spindle. Furthermore he will examine the epistatic relationship between Fgf and Wnt/PCP signaling in regulating cell polarity.