The Role of FGF Receptors in Lens Development

细胞分化、增殖和凋亡的调控是任何活的多细胞生物的基本要求。在小鼠和人类中，成纤维细胞生长因子（FGF）家族由编码22种不同配体和4种酪氨酸激酶受体（FGFR1-4）的基因组成。FGF刺激已被证明可诱导晶状体细胞的存活、增殖和分化。过表达几种不同FGF配体的转基因小鼠晶状体上皮发生异位分化。此外，Fgfr基因的条件性缺失会导致晶状体异常，这取决于哪个受体被缺失以及晶状体发育的哪个阶段发生缺失。在晶状体基板期单独删除Fgfr2并不会阻止晶状体纤维分化，但确实会导致晶状体细胞周期退出的轻微延迟，并损害晶状体细胞的存活。相反，在Fgfr3缺失的背景下，通过在晶状体囊泡阶段同时缺失Fgfr1和Fgfr2，可以阻止晶状体纤维分化。因此，FGFs和fgfr在晶状体生物学中起着至关重要的基础作用，是晶状体纤维分化所必需的。本应用的目的是检查Fgfr刺激后相关的生化途径，该途径介导了晶状体中fgf诱导的反应。待验证的假设是Fgfrs介导晶状体纤维分化的主要途径是通过激活中间对接蛋白FRS2alpha。这一假设将通过(1)直接修饰小鼠Fgfr2基因座以产生突变来进行验证：a)破坏与FRS2alpha的相互作用，b)破坏与PLCgamma的相互作用，c)与TrkC的细胞内结构域（一种也诱导FRS2alpha激活的受体）产生嵌合受体，并测试这些不同的突变Fgfr2基因是否能够在缺乏功能性Fgfr1和Fgfr3受体的情况下支持纤维分化反应；(2)对FRS2alpha基因进行条件突变，诱导该基因的晶状体特异性缺失；(3)在体内检测TrkC诱导晶状体上皮细胞纤维分化反应的能力。这一应用与公共卫生相关，因为白内障仍然是世界范围内最常见的致盲原因，FGF/FGFR信号在晶状体发育中起着至关重要的作用。FGF信号在包括癌症在内的许多疾病过程中也起着重要作用，但关于FGF如何引发其作用的分子细节尚未完全解决。

DESCRIPTION: The regulation of cell differentiation, proliferation and apoptosis is a fundamental requirement for any living multicellular organism. The fibroblast growth factor (FGF) family, in both mice and humans, consists of genes encoding 22 different ligands and four tyrosine kinase receptors (FGFR1-4). FGF stimulation has been shown to induce survival, proliferation and differentiation in cells of the ocular lens. Transgenic mice over-expressing several different FGF ligands undergo ectopic differentiation of the lens epithelium. Furthermore, conditional deletion of Fgfr genes leads to lens abnormalities depending on which receptor is deleted and what stage of lens development the deletion takes place. Deletion of Fgfr2 alone during the lens placode stage does not prevent lens fiber differentiation, but does cause a slight delay in lens cell cycle withdrawal and compromises lens cell survival. In contrast, on an Fgfr3 null background, lens fiber differentiation can be prevented by simultaneous deletion of Fgfr1 and Fgfr2 at the lens vesicle stage. Therefore, FGFs and FGFRs play a vital and fundamental role in lens biology and are absolutely required for lens fiber differentiation. The purpose of this application is to examine the relevant biochemical pathway, subsequent to Fgfr stimulation, that mediates FGF-induced responses in the lens. The hypothesis to be tested is that the major pathway by which Fgfrs mediate lens fiber differentiation is through the activation of the intermediate docking protein FRS2alpha. This hypothesis will be tested by (1) direct modification of the mouse Fgfr2 locus to create mutations designed to a) disrupt interaction with FRS2alpha, b) disrupt interaction with PLCgamma and c) create a chimeric receptor with an intracellular domain from TrkC (a receptor that also induces the activation of FRS2alpha) and testing to see if these different mutant Fgfr2 genes can or can not support a fiber differentiation response in the absence of functional Fgfr1 and Fgfr3 receptors; (2) making a conditional mutation in FRS2alpha and inducing lens-specific loss of this gene; (3) testing the ability of TrkC to induce a fiber differentiation response in lens epithelial cells in vivo. This application is relevant to public health because cataract remains the most frequent worldwide cause of blindness and FGF/FGFR signaling plays an essential role in lens development. FGF signaling also plays fundamental roles in many disease processes including cancer, but the molecular details of how FGFs elicit their effects are not fully resolved.