New Neurons in the Retina

描述（由申请人提供）：这个正在进行的研究项目的总体目标是了解在发育和再生过程中调节视网膜神经发生的细胞-细胞相互作用的分子基础。许多实验室在体内和体外以及许多不同脊椎动物物种中积累的证据表明，调节视网膜祖细胞分化的外部信号随发育年龄和视网膜位置而变化，并且视网膜祖细胞对外部信号的反应能力在视网膜发育过程中逐渐改变，反映了不同年龄视网膜祖细胞的内在变化。然而，在硬骨鱼中，视网膜神经发生持续整个成年期，所有类型的新神经元都是由位于远周视网膜纤毛边缘区（cmz）的多能视网膜祖细胞产生的，这表明即使是“早期出生”的视网膜细胞类型（例如，视网膜神经节细胞）的能力也被成年硬骨鱼视网膜的cmz中的视网膜祖细胞保留了下来。这些多能祖细胞表现出自我更新，可以产生所有视网膜细胞类型，并在损伤时被有丝分裂激活；因此，它们具有视网膜干细胞的所有特征。此外，在成年硬骨鱼的已分化的中央视网膜中，分散着与Muller胶质细胞相关的偶尔的、缓慢增殖的祖细胞，它们产生快速增殖的、谱系受限的杆状前体，这些前体迁移到外核层并产生新的杆状光感受器。鱼类视网膜中持续的神经发生能力与强大的再生能力有关：当硬骨鱼视网膜中的神经元被破坏时，在某些条件下它们会被替换。中央视网膜再生神经元的来源似乎是muller相关的视网膜祖细胞，因此也是视网膜干细胞。

DESCRIPTION (provided by applicant): The overall objective of this ongoing research program is to understand the molecular basis of cell-cell interactions that regulate retinal neurogenesis during development and regeneration. The accumulated evidence from many laboratories working both in vivo and in vitro and with a number of different vertebrate species suggests that extrinsic signals regulating the differentiation of retinal progenitor cells vary with developmental age and retinal location, and that the competence of retinal progenitors to respond to extrinsic cues is progressively altered during retinal development, reflecting intrinsic changes in retinal progenitors at different ages. However, in teleost fish, retinal neurogenesis continues throughout adult life, and new neurons of all types are generated from multipotent retinal progenitor cells located in the ciliary marginal zone (cmz) at the far peripheral retina, suggesting that the capacity to generate even the 'early born' retinal cells types (e.g., retinal ganglion cells) is retained by retinal progenitors in the cmz of the adult teleost retina. These multipotent progenitors exhibit self-renewal, can generate all retinal cell types, and are mitotically activated in response to injury; therefore, they have all the characteristics of retinal stem cells. In addition, scattered across the differentiated, central retina in adult teleost fish, and associated with Muller glial cells, are occasional, slowly proliferating progenitors, which give rise to clusters of rapidly proliferating, lineage-restricted rod precursors that migrate into the outer nuclear layer and generate new rod photoreceptors. The capacity for ongoing neurogenesis in the fish retina is associated with a robust ability to regenerate: when neurons in the teleost retina are destroyed, under certain conditions they are replaced. The source of regenerated neurons in central retina appears to be the Muller-associated retinal progenitors, which therefore are also retinal stem cells. The objectives of the proposed research are to: 1) define and characterize the molecular profiles of retinal stem cells and retinal progenitor cells in the embryonic and adult zebrafish (Danio rerio) retina, and establish the molecular/genetic hierarchy, 2) examine the phenotypic plasticity of Muller glial cells in response to retinal injury, and test the hypothesis that they function as retinal stem cells, and 3) identify the intrinsic and extrinsic factors that are necessary and sufficient to define the retinogenic potential of retinal stem cells. Understanding the molecular mechanisms controlling the proliferation and differentiation of retinal progenitors will have important value for the future development of therapeutic retinal transplantation in patients with retinal degenerative diseases or retinal injuries. Learning more about the characteristics and capabilities of retinal stem cells in the adult fish retina may provide important insights to help reach that goal.