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功能，既可以作为中枢神经系统的分化支持细胞，也可以作为常驻干细胞，在产生新的神经元之前经历去分化和增殖。动员胶质细胞成为干细胞样细胞是冷血脊椎动物（变温动物）（如鱼和青蛙）对眼睛生长、受伤或疾病的自然反应。相比之下，包括哺乳动物在内的温血脊椎动物（恒温动物）的神经胶质动员要有限得多。我们研究了小鼠视网膜中的神经胶质细胞活化，其中Muller神经胶质（MG）是干细胞的潜在来源。然而，通过MG自我修复机制的组织再生在恒温动物中并不容易发生。相反，MG对恒温动物损伤的有利反应是反应性胶质瘤，这是一种神经保护反应，可伴随细胞毒性作用。

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.