The role of cell polarity in vertebrate limb outgrowth

描述（由申请人提供）：肢体异常是最常见的出生缺陷之一，发生率约为0.7至1/1000。 因此，了解负责肢体正常生长和形成模式的机制对医学界具有极大的兴趣。 研究者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。 本申请专门研究了成纤维细胞生长因子（FGF）和Wnt/平面细胞极性（PCP）信号传导在建立肢体间充质细胞的肌动蛋白细胞骨架和有丝分裂纺锤体极性中的作用，作为肢体生长的基础机制。 一段时间以来，人们已经知道，沿着脊椎动物胚胎肢芽的远端边缘存在的外胚层组织的小脊是相邻肢间充质生长所必需的。 最近，已经证明分泌的成纤维细胞生长因子（FGF）家族的成员在该组织（称为顶端外胚层嵴或AER）中表达，并且对于肢体间充质的生长是必要的和足够的。 虽然FGF介导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引诱物而不是作为促有丝分裂因子或细胞存活因子来实现的。 FGF信号如何介导这种化学吸引？ 研究者已经收集了初步数据，表明AER信号激活肢体间充质中分泌的Wnt配体Wnt 5a的表达。 在鱼类和两栖动物模型中，Wnt 5a先前已被证明通过Wnt/平面细胞极性（PCP）途径发出信号。 Wnt/PCP信号在建立细胞极性中起关键作用，细胞极性是原肠胚形成期间定向细胞运动和细胞分裂的基础，对于延长胚胎轴至关重要。 他假设来自AER的Fgf信号在肢体间充质中建立了Wnt 5a表达的梯度，然后在这些细胞中建立极性，进而指导近端到远端的细胞运动和/或细胞分裂，导致肢体长出。 在本申请中，研究者将检验以下假设：Fgf和Wnt/PCP信号传导对于肌动蛋白细胞骨架或有丝分裂纺锤体的极化是必要且充分的。 此外，他将研究Fgf和Wnt/PCP信号传导在调节细胞极性方面之间的上位关系。

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.