Signaling systems that respond to cell-cell contact and regulate epithelial polarity

(Hayashi)为了了解管状器官器官发生过程中细胞运动控制的分子基础，我们开发了细胞膜和细胞膜成分的体内成像系统，并取得了以下发现：1)检测了小GTP酶Rac的体内功能。Rac的激活导致E-钙粘附素表达下调，并抑制上皮细胞的黏附和尖-基极性的丧失。2)以气管终支为模型研究了细胞质突起的伸展，发现终支伸展的刻板模式与表皮中定义位置信息的信号分子的表达有关。我们发现，终支的伸展是由表皮分泌的Hedgehog和Dpp引导的，从而使呼吸系统与其靶…正确匹配3)利用功能系统增益对调控上皮形态发生的基因进行大规模筛选。(Nagafuchi)为了了解细胞-细胞黏附在上皮细胞形成中的确切作用，用基因靶点方法研究了F9畸胎癌细胞系中钙粘附素-连环蛋白系统的功能。1)缺乏α-连环蛋白的F9细胞仍能形成紧密连接。结果表明，在没有钙粘连蛋白依赖的细胞-细胞黏附的情况下，可以形成紧密的连接。2)用基因敲除的方法评估了蛋白和β-连环蛋白的功能。缺乏β连环蛋白的F9细胞能够建立几乎完整的上皮。蛋白敲除导致桥粒形成缺陷。双基因敲除细胞未能表达许多上皮细胞特异性基因，这表明这两个基因在上皮细胞形成过程中是必不可少的。这一结果还表明，β-连环蛋白的功能可被白蛋白补偿。较少

(Hayashi) To understand the molecular basis for cell motility control during organogenesisi of tubular organs, we have developed an in vivo imaging system of cytosletetal and membrane components and made the following findings.1)In vivo function of the small GTPase RAC was examined. Activation of RAC caused down-regulation of E-cadherin expression and inhibited epithelial cell adhesion and a loss of apical-basal polarity. The results suggests that Rac is primarily involved in maintaining plasticity of epithelia to assure smooth remodeling during morphogenesis.2)Extension of cytoplasmic processes was studied using tracheal terminal branch as a model, and was found that the stereotyped pattem of terminal branch extension correlates with expression of signaling molecules defining positional information in the epidermis. We found that extension of terminal branch is guided by Hedgehog and Dpp that are secreted from the epidermis, thereby correct matching of respiratory system with its targ … More et organ.3)A large scale screening for genes regulating epithelial morphogenesis was performed using a gain of function system. Several novel gene activity controlling cell adhesion, cell motility and guidance were identified.(Nagafuchi) To understand the precise roles of cell-cell adhesion in the establishment of epithelia, the function of cadherin-catenin system was assessed by gene target approach in F9 teratocarcinome cell line.1)F9 cell deficient in alpha-catenin still able to form tight junction. The result suggets that tight junction can form in the absence of cadherin-catenin dependent strong cell-cell adhesion.2)Functions of plakoglobin and beta-catenin were assessed by the gene knockout approach. F9 cells deficient of beta catenin are able to establish nearly complete epithelia. Knockout of plakoglobin caused defects in desmosome formation. Double knockout cells failed to express many of epithelia-specific genes, suggesting essential requirement for those two genes in epithelia formation. The results also suggest that the function of beta catenin can be compensated by plakoglobin. Less