Regulation of apical constriction of bottle cells by the RhoGEF protein Plekhg5 during gastrulation morphogenesis

顶端收缩是一种细胞形状变化，与细胞进入、上皮弯曲有关 片材和管状结构的形成。它存在于许多形态发生过程中，例如 原肠胚形成、神经管闭合和感觉器官形成。心尖收缩失败可以 导致人类先天性疾病，如神经管缺陷。尽管心尖部很重要 在多种发育背景下的收缩，顶端收缩的分子调节因子不是 完全明白了。 Rho 信号传导先前已被认为与心尖收缩有关 脊椎动物神经管闭合和感觉基板内陷。然而，Rho 的一般激活 整个细胞不会导致顶端收缩，强调 Rho 的极化刺激 在特定的亚细胞区室中至关重要。 Rho 活动的空间调节通常是 由 Rho 监管机构 GEF 和 GAP 实现。 RhoGEF 和 RhoGAP 各有 20 多名成员 执行多种细胞功能。脊椎动物顶端收缩中 Rho 调节因子的身份 尚未明确定义，Rho 调节剂控制细胞形状变化的机制 没有详细描述。这种知识差距，加上根尖收缩的重要性 在胚胎发生中，需要进一步研究控制顶端的分子机制 收缩。在我们目前的研究中，我们将 plekhg5 鉴定为在瓶细胞中表达的 RhoGEF。 非洲爪蟾原肠胚形成期间的胚孔唇，具有调节顶端收缩的功能 瓶细胞。 Plekhg5 蛋白位于顶端并刺激顶端肌动球蛋白组装 当异位表达时，以 Rho 依赖性方式诱导异位胚孔唇。击倒 plekhg5 阻断胚泡唇部瓶细胞的顶端收缩并防止激活素 诱导外胚层中的胚孔唇。因此，Plekhg5 是瓶细胞中的内源性 RhoGEF， 参与原肠胚形成过程中顶端收缩的调节。 plekhg5 的活性为我们提供了 这是解决任何组织中有关根尖收缩的一些关键问题的绝佳机会 背景，即 Rho 调节因子如何被招募到特定的亚细胞区室以发挥作用 他们的职能（目标 1）；它们如何调节动态肌动球蛋白组织以协调还原 顶端细胞表面和粘附复合物重塑（目标 2）；以及下游有何不同 效应器参与调节肌动球蛋白动力学和细胞形状变化的不同方面 （目标 3）。完成拟议的研究将使我们更深入地了解顶端的分子控制 收缩并为我们提供了一个平台来研究和比较控制分子机制 不同组织环境中的顶端收缩。研究结果也可能有助于我们理解 由于顶端收缩缺陷导致上皮形态发生异常而引起的人类疾病。

Apical constriction is a cell shape change that associates with cell ingression, bending of epithelial sheet, and formation of tubular structures. It is found in many morphogenetic processes, such as gastrulation, neural tube closure, and sensory organ formation. Failure in apical constriction can cause human congenital diseases, such as neural tube defects. Despite the importance of apical constriction in multiple developmental contexts, molecular regulators of apical constriction are not understood completely. Rho signaling has been implicated previously in apical constriction during vertebrate neural tube closure and sensory placode invagination. However, general activation of Rho throughout a cell does not lead to apical constriction, underscoring that polarized stimulation of Rho within particular subcellular compartment is crucial. Spatial regulation of Rho activities is normally achieved by Rho regulators GEFs and GAPs. Over 20 members each of RhoGEFs and RhoGAPs perform diverse cellular functions. The identity of Rho regulators in apical constriction in vertebrates is not well defined, and the mechanisms via which Rho regulators act to control cell shape changes are not described in detail. This knowledge gap, combined with the importance of apical constriction in embryogenesis, demands further investigation about molecular machinery controlling apical constriction. In our current study, we identified plekhg5 as a RhoGEF expressed in the bottle cells of the blastopore lip during Xenopus gastrulation and had a function in regulating apical constriction of the bottle cells. Plekhg5 protein is apically localized and stimulates apical actomyosin assembly to induce ectopic blastopore lip in a Rho-dependent fashion when ectopically expressed. Knockdown of plekhg5 blocks apical constriction of bottle cells at the blastopore lip and prevents activin from inducing blastopore lip in the ectoderm. Plekhg5 is thus an endogenous RhoGEF in bottle cells that participates in regulation of apical constriction during gastrulation. The activity of plekhg5 provides us an excellent opportunity to address some of the key issues regarding apical constriction in any tissue contexts, namely how Rho regulators are recruited to particular subcellular compartment(s) to exert their function (aim 1); how they modulate dynamic actomyosin organization to coordinate reduction of apical cell surface and adhesion complex remodeling (aim 2); and how different downstream effectors are involved in regulating distinct aspects of actomyosin dynamics and cell shape changes (aim 3). Completion of the proposed studies will offer us deeper insight into molecular control of apical constriction and provide us a platform to investigate and compare molecular mechanisms governing apical constriction in diverse tissue contexts. The results may also contribute to our understanding of human diseases caused by abnormal epithelial morphogenesis due to defects in apical constriction.