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

根尖狭窄是一种细胞形态改变，与细胞内移、上皮细胞弯曲有关 薄板和管状结构的形成。它存在于许多形态发生过程中，例如 原肠发育、神经管闭合和感觉器官形成。根尖狭窄失败可 导致人类先天疾病，如神经管缺陷。尽管心尖部的重要性 在多个发育背景下的收缩，根尖收缩的分子调节器不是 完全明白。Rho信号此前曾与心尖部收缩有关 脊椎动物神经管闭合和感觉胎盘内陷。然而，Rho的普遍激活 整个细胞不会导致心尖收缩，强调了Rho的极化刺激 在特定的亚细胞隔间内是至关重要的。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。脊椎动物根尖收缩中Rho调节因子的特性 以及Rho调节器控制细胞形状变化的机制 都没有详细描述。这一认识差距，再加上根尖狭窄的重要性 在胚胎发生中，控制心尖的分子机制需要进一步的研究 收缩。在我们目前的研究中，我们鉴定了plekhg5是一种在瓶装细胞中表达的Rhogef 非洲爪哇原肠发育过程中的胚孔唇及其对根尖收缩的调节作用 瓶子细胞。Plekhg5蛋白位于顶端并刺激顶端肌球蛋白组装以 当异位表达时，以Rho依赖的方式诱导异位胚孔嘴唇。击倒 Plekhg5阻止胚孔唇部瓶状细胞的顶端收缩，防止激活素 在外胚层中诱导胚孔唇。因此，Plekhg5是瓶子细胞中的内源性Rhogef， 参与原肠发育过程中顶端收缩的调节。PUKHG5为我们提供了 这是一个极好的机会来解决关于任何组织的根尖狭窄的一些关键问题 语境，即Rho调节剂如何被招募到特定的亚细胞隔间(S)发挥作用 它们的功能(目标1)；它们如何调节动态肌球蛋白组织以协调还原 顶端细胞表面和黏附复合体重塑(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)。拟议研究的完成将使我们对心尖细胞的分子调控有更深入的了解。 构建并为我们提供了一个研究和比较分子机制的平台 在不同的组织环境中的根尖收缩。这一结果也有助于我们理解 由根尖狭窄缺陷引起的上皮形态发生异常引起的人类疾病。

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.