Spatiotemporal regulation of collective cell behaviors in Drosophila

正常组织发育和肿瘤转移需要广泛的细胞运动，并且边缘细胞 果蝇卵巢中的迁移提供了强有力的体内模型。边缘细胞以两个为一组迁移 不同的细胞类型，一对非迁移性极细胞在中心，招募6-8上皮细胞包围 并将它们在滋养细胞之间运送到发育中的卵母细胞，在一个称为卵室的结构中。使用 在这个系统中，我们首先发现了21 kD GTdR ac在体内突起和迁移中的作用， 表明一个细胞中Rac的光活化可以控制整个簇。二十多年来 然而，我们感到困惑的是，边缘细胞中组成型活性Rac的表达似乎破坏了细胞的功能。 整个卵室。在目前的融资期间，我们解决了这个长期存在的谜团。我们发现 表达活性Rac的边缘细胞杀死了滋养细胞。前卵泡细胞通常吞噬和杀死护士 细胞在卵子发生后期，我们提出，活跃的Rac过早地激活了这个程序。类似的 这一机制可以解释人类患者神秘的免疫缺陷。在此，我们建议 继续我们令人兴奋的Rac介导的细胞迁移的时空控制研究， 吞噬果蝇在目的1中，我们提出阐明Rac介导的细胞杀伤机制。 利用边界细胞模型，我们将测试每个已知的激活的功能效应。 导致患者免疫缺陷的Rac突变。我们将检验边缘细胞 表达活性Rac过早激活正常的发育杀伤程序，我们将定义 更确切地说，Rac在分子途径中的作用。我们将研究六个细胞如何 破坏整个卵室，我们将确定化学，物理和粘合剂特性， 控制目标细胞的选择。在目标2中，我们建议跟进我们的发现，即基底局部化的Rac 激活剂是边界细胞簇内聚和迁移所必需的。我们将阐明它与 基底外侧复合物蛋白，并测试其主要功能是否是将Rac活性定位于基底 表面。我们将检验这样的假设，即基底Rac活性是产生基底突起所必需的， 转动协调集体细胞行为。在目标3中，我们将跟进一个屏幕， 边缘细胞所需的Rho家族激活剂和抑制剂。我们建议边界细胞需要精心设计 Rac的时空控制，因为它们需要：尽管分离，但仍保持顶基极性 从基底膜，延伸和缩回向前的突起，在应变下保持凝聚力， 并抑制不适当的突出。我们的最终目标是破译Rac监管网络。

Normal tissue development and tumor metastasis require extensive cell movements, and border cell migration in the Drosophila ovary provides a powerful in vivo model. Border cells migrate as a group of two different cell types, a pair of non-migratory polar cells in the center that recruit 6-8 epithelial cells to surround and carry them between nurse cells to the developing oocyte, in a structure called an egg chamber. Using this system, we first discovered the in vivo role of the 21kD GTPase Rac in protrusion and migration, then showed that photoactivation of Rac in one cell could steer the entire cluster. For more than two decades though, we were puzzled that expression of constitutively active Rac in border cells seemed to destroy the entire egg chamber. During the current funding period, we solved this longstanding mystery. We discovered that border cells expressing active Rac kill the nurse cells. Anterior follicle cells normally engulf and kill nurse cells late in oogenesis, and we propose that active Rac prematurely activates this program. A similar mechanism may explain otherwise mysterious immune deficiencies in human patients. Here we propose to continue our exciting investigation of the spatiotemporal control of Rac-mediated cell migration and engulfment in Drosophila. In Aim 1 we propose to elucidate the mechanisms of Rac-mediated cell killing. Taking advantage of the border cell model, we will test the functional effects of each of the known activating Rac mutations that cause immunodeficiencies in patients. We will test the hypothesis that border cells expressing active Rac prematurely activate the normal developmental killing program, and we will define more precisely the role of Rac within the molecular pathway. We will investigate how just six cells can destroy an entire egg chamber, and we will identify the chemical, physical, and adhesive properties that govern target cell selection. In Aim 2, we propose to follow up on our discovery that a basally localized Rac activator is required for border cell cluster cohesion and migration. We will elucidate its relationship to basolateral complex proteins and test whether its primary function is to localize Rac activity to basal surfaces. We will test the hypothesis that basal Rac activity is required to generate basal protrusions that in turn coordinate collective cell behavior. In Aim 3, we will follow up on a screen in which we have identified Rho family activators and inhibitors required in border cells. We propose that border cells require elaborate spatiotemporal control of Rac due to their needs to: maintain apicobasal polarity despite being detached from basement membrane, extend and retract forward-directed protrusions, maintain cohesion under strain, and inhibit inappropriate protrusion. Our ultimate goal is the decipher the Rac regulatory network.