The role of the atypical cadherin Fat2 in establishing planar cell polarity in the Drosophila follicle epithelium

组织或体轴的延长是动物发育过程中的一个基本过程。组织伸长通常需要用来确定伸长轴的平面极性信息。然后执行组织伸长，涉及单个细胞行为，包括定向细胞形状改变、定向细胞分裂或细胞重排。平面极性信息是如何指导细胞行为的，目前还知之甚少。研究组织伸长的一个有用的模型系统是果蝇卵巢，在卵巢中，未来的卵子作为卵室的一部分发育。卵室最初是球形的，但随后拉长以获得其特有的椭圆形。不能伸长会导致球形卵子和雌性不育。每个卵室由生殖系细胞和围绕生殖系细胞的单层上皮滤泡细胞组成。我们以前已经证明，卵室的延长需要滤泡细胞中非典型钙粘附素Fat2的活性。FAT2在组织中建立了一个平面极性，用于组织毛囊细胞的细胞骨架和细胞外基质。平面极化的细胞骨架和细胞外基质有助于卵室的延长。然而，Fat2如何建立这种平面极性以及如何在单个细胞行为水平上执行伸长仍然知之甚少。这项提议有两个目的。首先，揭示Fat2在卵泡上皮细胞中建立平面极性的分子机制。第二，揭示卵泡细胞在卵室伸长过程中的行为和动态。为了解决第一个目标，我们将进行结构-功能-分析，以确定Fat2蛋白的关键区域，该区域是建立平面极性信息和卵室延伸所需的。为了解决第二个目标，我们已经建立了使用单平面照明显微镜(SPIM)对活的卵室进行全套成像的方法。我们将使用这种方法来可视化和定量分析毛囊细胞的行为和动力学。我们将确定毛囊细胞是否经历定向细胞形状变化、定向细胞分裂或细胞重排。我们将进一步分析这些个体细胞行为对卵室整体伸长的贡献。此外，为了确定Fat2促进卵室延长的细胞机制，我们将比较野生型和Fat2突变卵室中的细胞行为。我们预计这些研究将为将平面极性信息与个体细胞行为和组织规模的形态发生联系起来的机制提供新的见解。

The elongation of tissues or body axes is a fundamental process during animal development. Tissue elongation often requires planar polarity information that is used to establish the axis of elongation. Tissue elongation is then executed involving individual cell behaviors including directed cell shape changes, oriented cell divisions, or cell rearrangements. How planar polarity information directs cell behavior is poorly understood. A useful model system to study tissue elongation is the Drosophila ovary, in which the future egg develops as part of an egg chamber. Egg chambers are initially spherical in form, but then elongate to obtain their characteristic elliptical shape. Failure to elongate results in spherical eggs and female sterility. Each egg chamber is composed of germ line cells and a single layer of epithelial follicle cells surrounding the germ line cells. We have shown previously that egg chamber elongation requires the activity of the atypical cadherin Fat2 in follicle cells. Fat2 establishes a planar polarity in the tissue that is used to organize the cytoskeleton and the extracellular matrix of follicle cells. The planar polarized cytoskeleton and extracellular matrix contribute to egg chamber elongation. However, how Fat2 establishes this planar polarity and how the elongation is executed at the level of individual cell behaviors remains poorly understood. This proposal has two aims. First, to reveal the molecular mechanism by which Fat2 establishes planar polarity in the follicle epithelium. Second, to reveal the behavior and dynamics of follicle cells during egg chamber elongation. To address the first aim, we will perform a structure-function-analysis to identify critical regions of the Fat2 protein required for the establishment of planar polarity information and egg chamber elongation. To address the second aim, we have established in toto imaging of living egg chambers using Single Plane Illumination Microscopy (SPIM). We will use this method to visualize and quantitatively analyze the behavior and dynamics of follicle cells. We will determine whether follicle cells undergo directed cell shape changes, oriented cell divisions or cell rearrangements. We will furthermore analyze the contribution of these individual cell behaviors to the overall elongation of the egg chamber. Moreover, to identify the cellular mechanisms by which Fat2 contributes to egg chamber elongation, we will compare cell behaviors in wild-type and fat2 mutant egg chambers.We expect that these studies will provide novel insights into the mechanisms that link planar polarity information to individual cell behaviors to tissue-scale morphogenesis.