Regulation of embryonic epithelial morphogenesis

描述(申请人提供)：极化上皮的形成是胚胎发育的基础。在小鼠围着床期发育过程中，胚泡内未分化的细胞团从非极性的细胞团转化为高度组织化的上皮性囊泡。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。 从胚胎干细胞分化而来的体外培养的类胚体(EBS)可以概括小鼠围着床期的发育情况。利用转基因的EBS，我们首次证明了BM的形成指导了黏附复合体的组装，黏附复合体作为调节上胚极化和存活的信号平台。我们的初步数据支持这一观点，表明(1)BM相关黏附复合体的组装与Rho GTP酶CDC42和rac1的激活相关；(2)Cdc42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必需的过程；以及(3)rac1激活在依赖BM的上皮细胞存活中发挥重要作用。这些数据有力地支持了我们的假设，即BM的形成诱导了上胚极化，并通过激活CDC42和rac1促进了上胚细胞的存活。为了验证这一假设，我们建议确定BM相关黏附复合体的组装诱导CDC42和rac1激活的机制(特定目标1和3)。接下来，我们将确定调控外胚细胞伸长和顶端极化的CDC42-效应器相互作用，重点放在IQGAP1在微管捕获和外囊在顶端极性蛋白运输中的作用(特定目标2)。最后，我们将确定调节上皮细胞存活的rac1-效应器相互作用(特定目标4)。 这项研究的长期目标是确定调控胚胎上皮形态发生的细胞外信号和跨膜级联，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，将细胞的极性、分化和存活与组织结构结合在一起，不仅对我们理解胚胎发育和癌症生物学至关重要，而且对组织再生和组织工程也有重要意义。

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.