Elucidating the molecular mechanisms that control Muller glia activation in the retina

概述：神经胶质细胞具有非凡的能力，既可以作为中枢神经系统中的分化支持细胞，也可以作为常驻干细胞，在产生新神经元之前经历去分化和增殖。在鱼类和青蛙等冷血脊椎动物中，动员神经胶质细胞成为干细胞样细胞是对眼睛生长、损伤或疾病的自然反应。相比之下，神经胶质细胞的动员在温血脊椎动物(恒温动物)中要有限得多，包括哺乳动物。我们研究了小鼠视网膜中胶质细胞的激活，穆勒胶质细胞(MG)是干细胞的潜在来源。然而，通过MG自愈修复机制的组织再生在吸热状态下并不容易发生。相反，在恒温状态下，MG对损伤的反应是反应性胶质增生，这是一种神经保护反应，可以伴随细胞毒效应。*为了解释哺乳动物MG是如何做出选择的，要么作为分化的支持细胞，要么作为干细胞重新进入细胞周期，或者经历反应性胶质增生，我们关注锌指转录因子Zac1。我们发现，在Zac1缺失突变小鼠中，MG经历了非损伤的胶质细胞增殖症。Zac1是母系印记基因，是共同调控基因印记基因网络(IGN)的一部分。因此，我们假设Zac1维持MG处于静止、分化状态，通过IGN发挥作用，防止反应性胶质细胞增生，并可能进行干细胞修复。为了验证这一假设，我们将：*目标1.评估Zac1在维持分化的MG表型中的正常作用。我们通过表征Zac1突变MG的命运和评估其对非损伤诱导提示的反应性来评估Zac1在维持未损伤眼的分化MG命运中的作用。*目的2.检测Zac1在MG损伤反应中的作用。为了确定Zac1是否参与了损伤依赖型MG的反应，我们评估了Zac1在不同应激源下的表达，并询问Zac1的过度表达在MG中是否具有保护作用。*目的3.确定Zac1是否通过IGN维持成熟的MG表型。为了测试Zac1是否通过IGN维持MG的分化状态，我们研究了IGN基因在Zac1突变MG和损伤模型中的表达，并进行了IGN功能测试和功能丧失和获得的研究。*影响：该项目将加强我们对MG生物学的基础知识，并应用于干细胞生物学和组织再生的一般领域。HQP将接触到创新和最先进的技术，使他们在当今以知识为基础的经济中具有竞争力。**

Overview: Glial cells have an extraordinary ability to function either as differentiated support cells in the central nervous system, or as resident stem cells, undergoing de-differentiation and proliferation before giving rise to new neurons. Mobilization of glial cells to become stem cell-like is a natural response to eye growth, injury or disease in cold-blooded vertebrates (ectotherms), such as fish and frogs. In contrast, glial mobilization is much more limited in warm-blooded vertebrates (endotherms), including mammals. We study glial cell activation in the murine retina, where Muller glia (MG) are a potential source of stem cells. However, tissue regeneration via a MG self-healing repair mechanism does not occur readily in endotherms. Instead, the favored response of MG to injury in endotherms is reactive gliosis, a neuroprotective response that can have accompanying cytotoxic effects.******To decipher how mammalian MG make the choice to either remain as differentiated support cells, re-enter the cell cycle as stem cells, or undergo reactive gliosis, we focus on the zinc finger transcription factor Zac1. We found that MG undergo injury-independent gliosis in Zac1 null mutant mice. Zac1 is a maternally imprinted gene and part of an imprinted gene network (IGN) of co-regulated genes. We thus hypothesize that Zac1 maintains MG in a quiescent, differentiated state, acting via the IGN to prevent reactive gliosis and possibly stem cell-repair. To test this hypothesis we will:******Aim 1. Assess the normal role of Zac1 in maintaining a differentiated MG phenotype. We assess Zac1 function in maintaining a differentiated MG fate in the uninjured eye by characterizing the fate of Zac1 mutant MG and by assessing their responsiveness to non-injury inductive cues.***Aim 2. Examine the role of Zac1 in the MG injury response. To determine whether Zac1 participates in injury-dependent MG responses, we assess Zac1 expression in response to various stressors, and ask whether Zac1 overexpression is protective in MG. ***Aim 3. Determine whether Zac1 acts through the IGN to maintain a mature MG phenotype. To test whether Zac1 acts through the IGN to maintain MG in a differentiated state, we study the expression of IGN genes in Zac1 mutant MG and injury models, and perform IGN functional tests with loss- and gain-of-function studies.******Impact: This project will enhance our fundamental knowledge of MG biology, with applications to the general field of stem cell biology and tissue regeneration. HQP will be exposed to innovative, state-of-the-art techniques that will allow them to be competitive in today's knowledge-based economy.**