Genetics and Molecular Mechanisms Underlying Overgrowth Disorders of the Limb

摘要 在发育过程中协调生长和分化对于正常的机械和 器官和附属物的生理功能。尽管它很重要，但监管如何协调 增长发生的时候，比例保持不变还没有得到很好的理解。为了深入了解这一过程，我们 研究了以指节局部巨大症为特征的先天性巨指发育障碍。 手脚并用。巨指症是一种独特的生长障碍，其骨骼和软组织元素 包括神经、血管、肌肉和骨骼在内的手指是增大的，然而，更大的手指是这样组织起来的 形式。因此，巨指症患者代表着一个独特的探索基础的生物学机会。 生长、大小和比例如何在组织内和组织间协调的机制。我们有 在磷脂酰肌醇3激酶(PI3K)的催化亚基中发现了一种特定的体细胞激活突变， 由基因PIK3CA编码，在巨指症患者的受影响组织中。这种突变也是常见的 发现在癌症和其他过度生长障碍中；因此，这种突变本身不能解释协调的 大拇指畸形的生长反应。这种特殊的突变是如何导致过度生长的 在四肢的发育过程中协调并形成图案？过度生长对数字的限制 这些患者与近侧肢体相反，提示远侧肢体中的组织相互作用在 发育来调节花纹的生长和大小。此外，我们已经确定了潜在的修饰者 与PIK3CA共同产生的突变可能是PI3K调节过度生长所必需的。我们 假设PI3K介导的信号通过特定的旁分泌信号协调生长 感觉神经组织在发育过程中依赖于顶端之间的信号 肢体发育过程中的外胚层脊(AER)和间充质组织。我们建议调查 PI3K通过以下途径调节协调生长：1)鉴定和定位受影响的细胞和 巨指畸形患者体内含有突变型PIK3CA的组织及其对其影响的检测 2)使用新的斑马鱼模型来剖析斑马鱼的遗传和发育原因 通过系统分析新发现的调节PIK3CA的次级修饰物突变来实现过度生长 3)使用激活的PIK3CA的条件性敲击小鼠模型来测试PIK3CA的充分性 在发育中的小鼠肢体的特定组织中增加PI3K信号，以表现为大拇指。这个 拟议的研究将定义对器官大小和生长的分子和组织水平的调节，这将导致 针对一系列过度生长和肿瘤疾病的新治疗方法，并产生新的治疗策略 促进组织修复和器官再生。

Summary The orchestration of growth and differentiation during development is essential for normal mechanical and physiological function of organs and appendages. Despite its importance, the regulation of how coordinated growth occurs such that proportion is maintained is not well understood. To gain insight into this process, we studied the congenital overgrowth disorder macrodactyly characterized by local giganticism of the digits of the hand and feet. Macrodactyly is a unique growth disorder in that the skeletal and soft tissue elements of the digits including nerve, vasculature, muscle and bone are enlarged, however organized such that larger digits form. Thus, patients with macrodactyly represent a unique biologic opportunity to explore fundamental mechanisms of how growth, size and proportion are coordinated within and between tissues. We have identified a specific somatic activating mutation in the catalytic subunit of phosphoinositide 3 kinase (PI3K), encoded by the gene PIK3CA, within affected tissue of macrodactyly patients. This mutation is also commonly found in cancer and other overgrowth disorders; thus, this mutation alone cannot explain the coordinated growth response observed in macrodactyly. How does this particular mutation lead to overgrowth that is coordinated and patterned during the development of the limbs? The restriction of overgrowth to the digits in these patients as opposed to the proximal limb, suggests a role for tissue interactions in the distal limb during development to regulate patterned growth and size. Additionally, we have identified potential modifier mutations arising in concert with PIK3CA that may be essential for PI3K regulation of overgrowth. We hypothesize that PI3K-mediated signaling coordinates growth through specific paracrine signaling from sensory neural tissues during development in a manner that is dependent on signaling between the apical ectodermal ridge (AER) and mesenchymal tissues during limb development. We propose to investigate the regulation of coordinated growth by PI3K through: 1) identification and localization of the affected cells and tissues containing mutant PIK3CA in macrodactyly patients and examination of the effect of these mutant cells on adjacent tissues; 2) use of novel zebrafish models to dissect the genetic and developmental causes of overgrowth though systematic analysis of newly identified secondary modifier mutations in regulating PIK3CA function and 3) the use of a conditional knockin mouse model of activated PIK3CA to test the sufficiency of increased PI3K signaling within specific tissues of the developing mouse limb to phenocopy macrodactyly. The proposed research will define the molecular and tissue level regulation of organ size and growth that will lead to new treatment modalities for a host of overgrowth and neoplastic conditions and yield new strategies for enhancing tissue repair and organ regeneration.