Regulation of embryonic epithelial morphogenesis

极化上皮的形成是胚胎发育的基础。在小鼠围产期- 着床发育时，囊胚未分化的内细胞团从 非极性细胞聚集成高度组织化的上皮性囊泡。这种形态发生的转变 涉及上皮细胞的极化和基底膜(BM)依赖的存活。 然而，这些过程背后的分子机制在很大程度上是未知的。 体外培养类胚体可再现小鼠围着床期发育 (EBS)从胚胎干细胞分化而来。使用转基因EBS，我们首次展示了 BM形成指导黏附复合体组装的时间，黏附复合体作为信号 调节外胚极化和存活的平台。我们的初步数据支持这一观点， 证明(1)BM相关黏附复合体的组装与 Rho GTP酶CDC42和rac1的激活；(2)CDC42控制微管的组织和 顶端极性蛋白的运输，这是细胞伸长和极化所需的过程； (3)rac1的激活在BM依赖的上胚细胞存活中起重要作用。这些数据强烈地 支持我们的假设，即骨髓形成诱导上胚极化并促进上胚存活 通过激活CDC42和rac1。为了检验这一假设，我们建议确定其机制 BM相关黏附复合体的组装可诱导CDC42和rac1的激活 (具体目标1和3)。接下来，我们将确定调控外胚层的cdc42-效应器相互作用。 延长和顶端极化，重点是IQGAP1在微管捕获中的作用和 顶端极性蛋白运输中的胞囊(特定目标2)。最后，我们将确定rac1- 调节上胚层存活的效应器相互作用(特定目标4)。 这项研究的长期目标是确定细胞外信号和跨膜级联 调节胚胎上皮形态发生，这对我们理解上皮细胞至关重要 生物学、胚胎发生和组织再生。整合细胞的胚胎上皮组织形成的分子机制 极性、分化和组织结构的生存不仅对我们理解 胚胎发育和癌症生物学，但对组织再生和组织也有影响 工程学。

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 regulates 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. 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.