Regulation of embryonic epithelial morphogenesis

描述（由申请人提供）：极化上皮的形成是胚胎发育的基础。在小鼠胚泡着床发育过程中，胚泡未分化的内细胞团由非极性细胞聚集体转化为高度组织化的上皮囊肿。这种形态发生转化涉及上胚层上皮的极化和基底膜（BM）依赖性存活。然而，这些过程背后的分子机制在很大程度上是未知的。 体外培养胚胎干细胞分化的拟胚体（EBs）可以再现小鼠围着床期的发育过程。使用基因修饰的EB，我们首次表明，BM的形成指导组装的粘附复合物，作为一个信号平台，以调节上胚层极化和生存。我们的初步数据支持这一观点，表明（1）BM相关粘附复合物的组装与Rho GTP酶Cdc 42和Rac 1的激活相关;（2）Cdc 42控制微管组织和顶端极性蛋白的运输，这是细胞伸长和极化所需的过程;（3）Rac 1激活在BM依赖的上胚层存活中起着至关重要的作用。这些数据有力地支持了我们的假设，即BM形成诱导上胚层极化，并通过激活Cdc 42和Rac 1促进上胚层存活。为了验证这一假设，我们建议确定BM相关粘附复合物的组装诱导Cdc 42和Rac 1激活的机制（具体目标1和3）。接下来，我们将确定Cdc 42效应器的相互作用，调节上胚层伸长和顶端极化，重点是IQGAP 1在微管捕获和顶端极性蛋白质运输的外囊中的作用（具体目标2）。最后，我们将确定Rac 1-效应物相互作用，调节外胚层生存（具体目标4）。 本研究的长期目标是确定细胞外信号和调节胚胎上皮形态发生的跨膜级联，这对我们理解上皮生物学、胚胎发生和组织再生至关重要。 公共卫生相关性：阐明胚胎上皮组织形成的分子机制，整合细胞极性，分化和生存与组织结构不仅是我们了解胚胎发育和癌症生物学的关键，而且在组织再生和组织工程的影响。

DESCRIPTION (provided by applicant): Formation of polarized epithelium is fundamental to embryonic development. During mouse peri- implantation development, the undifferentiated inner cell mass of the blastocyst is converted from a nonpolar cell aggregate to a highly organized epithelial cyst. This morphogenetic transformation involves the polarization and basement membrane (BM)-dependent survival of epiblast epithelium. However, the molecular mechanisms underlying these processes are largely unknown. The mouse peri-implantation development can be recapitulated by in vitro cultured embryoid bodies (EBs) differentiated from embryonic stem cells. Using genetically modified EBs, we show for the first time that BM formation directs the assembly of an adhesion complex, which serves as a signaling platform to regulate epiblast polarization and survival. Our preliminary data supporting this idea, demonstrating that (1) assembly of the BM-associated adhesion complexes correlates with the activation of Rho GTPases Cdc42 and Rac1; (2) Cdc42 controls microtubule organization and the trafficking of apical polarity proteins, processes that are required for cell elongation and polarization; and (3) Rac1 activation plays an essential role in BM-dependent epiblast survival. These data strongly support our hypothesis that BM formation induces epiblast polarization and promotes epiblast survival via activation of Cdc42 and Rac1. To test this hypothesis, we propose to determine the mechanism through which the assembly of BM-associated adhesion complexes induces Cdc42 and Rac1 activation (Specific Aim 1 and 3). Next, we will determine the Cdc42-effector interactions that regulate epiblast elongation and apical polarization, focusing on the role of IQGAP1 in microtubule capture and the exocyst in apical polarity protein trafficking (Specific Aim 2). Finally, we will determine the Rac1- effector interactions that regulate epiblast survival (Specific Aim 4). The long-term goal of this study is to identify the extracellular cues and the transmembrane cascades that regulate embryonic epithelial morphogenesis, which are crucial to our understanding of epithelial biology, embryogenesis, and tissue regeneration. Public Health Relevance: Elucidating the molecular mechanisms of embryonic epithelial tissue formation that integrate cellular polarity, differentiation and survival with tissue architecture is not only critical to our understanding of embryonic development and cancer biology but also has implications in tissue regeneration and tissue engineering.