MOLECULAR STUDIES OF RETINAL DEVELOPMENT

神经元多样性的获得是发育的核心， 哺乳动物中枢神经系统（CNS）的组织。 我们 了解这种多样性的一些机制， 神经元的研究极大地促进了这一目标的实现。 分化的视网膜，一个良好的表征模型的中枢神经系统。 利用逆转录病毒进行体内神经元前体细胞谱系分析 感染和进行性谱系限制 规范. 然而，我们对生物学的分子基础的理解， 由于缺乏有关信息，这些过程仍不清楚， 参与哺乳动物神经发生的基因。 其中一种方法是 鉴定和研究哺乳动物视网膜特异性表达， 果蝇基因的同源物，其在神经发生中的作用已经被很好地 通过突变分析建立的。 根据他们的时空 这些基因在早期神经发生中的表达和功能 两个不同的类，无毛鳞片的原神经基因（AS-C） 编码碱性螺旋-环-受阻转录因子的复合物 （bHLH）类和Notch是其成员的神经原性基因， 编码一种膜蛋白 前神经性和神经源性 基因已经被证明在发育中起着重要的作用， 果蝇的眼睛 这些基因在早期神经发生中的功能， 一般来说，特别是在眼睛的发展中， 哺乳动物同系物的理想候选人的调查 AS-C和Notch的哺乳动物同源物的时空表达 基因在发育中的视网膜，以了解他们的细胞特异性 表达，并制定一个关于其功能的假设。 两 基因可能参与介导细胞间的相互作用， 视网膜神经发生和细胞类型特化。 而AS-C同系物 可以通过影响基因组来激活分化程序， 另一方面，HAD可以将基因组的激活与 分化发生的微环境。 为了 为了评估这种可能性，这些基因的表达将被 在体外研究了对各种生长因子的反应， 显示调节视网膜中的细胞增殖和分化。 的 AS-C同源物，类似于肌源性基因，MyoD可能作为主基因发挥作用。 调节基因参与下游神经元特异性 基因在神经发生的早期阶段。 这 通过分析AS-C的能力，对假设进行初步检验 在发育中的视网膜中表达的同源物与推定的顺式相互作用 作用元件（E-box），并通过以下方法评估其转录活性： 反式激活实验 这一信息将是至关重要的 下游神经元特异性基因的鉴定和AS的评估- C同源物的表达是神经发生的节点。 的研究 Notch和AS-C基因在视网膜发育过程中的同源物将有助于 我们的长期目标是全面了解 神经发生和细胞类型特化的分子事件。 从这些研究中获得的信息将有助于我们了解 一些涉及视网膜变性的过程， 关于分子和细胞水平干预的假设 通过重演延长和促进特定神经元的存活 视网膜退化的发展机制。

The acquisition of neuronal diversity is central to the development and organization of the mammalian central nervous system (CNS). Our understanding of some of the mechanisms by which this diversity is achieved has been greatly facilitated by studies of neuronal differentiation in retina, a well characterized model of the CNS. Lineage analyses of neuronal precursors in vivo using retroviral infections and progressive lineage restriction during cell-type specification. However, our understanding of the molecular basis of these processes remains unclear for the lack of information regarding genes involved in the mammalian neurogenesis. One of the approaches is to identify and study the retina-specific expression of the mammalian homologs of Drosophila genes whose role in neurogenesis has been well established by mutation analyses. Depending upon their spatio-temporal expression and functions during early neurogenesis these genes belong to two different classes, the proneural genes of the achaete-scute (AS-C) complex that encode transcription factors of basic Helix-Loop-Helix (bHLH) class and the neurogenic genes of which Notch is a member, that encodes a membrane protein. Members of both proneural and neurogenic genes have been shown to play important roles in the development of Drosophila eye. The function of these genes in early neurogenesis in general and in the development of the eye in particular make their mammalian homologues ideal candidates for the investigation of the spatio-temporal expression of the mammalian homologs of AS-C and Notch genes in developing retina in order to know their cell-specific expression and to formulate a hypothesis regarding their function. Both genes may be involved in mediating intercellular interactions during retinal neurogenesis and cell-type specification. While AS-C homologs can activate the differentiation program by influencing the genome, Notch on the other had can link the activation f the genome with microenvironment in which the differentiation is taking place. In order to evaluate such possibilities, the expression of these genes will be studied in vitro in response to various growth factors that have been shown to modulate cell proliferation and differentiation in retina. The AS-C homologs, analogous to myogenic gene, MyoD may function as master regulatory genes involved in the activation of downstream neuron-specific genes in precursors during the early stages of neurogenesis. This hypothesis will lbs initially tested by analyzing the ability of AS-C homologs expressed in developing retina to interact with putative cis- acting elements (E-box) and evaluating their transcriptional activity by transactivation experiments. This information will be critical for the identification of downstream, neuron-specific genes and evaluation of AS- C homologs expression as the nodal point in neurogenesis. Studies of the homologs of Notch and AS-C genes during the retinal development will help us in our long term goal of obtaining a comprehensive picture of the molecular events underlying neurogenesis and cell-type specification. The information obtained from these studies will help us in understanding some of the processes involved in retinal degeneration and formulated hypotheses regarding interventions at the molecular and cellular levels to prolong and promote the survival of specific neurons by recapitulation of developmental mechanisms during retinal degeneration.