Fadool James M
Department of Biological Science, The Florida State University, Tallahassee, FL 32306-4340, USA.
Dev Biol. 2003 Jun 15;258(2):277-90. doi: 10.1016/s0012-1606(03)00125-8.
The number and distribution of neurons within the vertebrate retina are tightly regulated. This is particularly apparent in the highly ordered, crystalline-like arrangement of the cone photoreceptors in the teleost. In this report, using a transgenic line of zebrafish, a novel and developmentally regulated mosaic pattern of the rod photoreceptors is described. The spatial and temporal expression of EGFP, under the control of the Xenopus rhodopsin gene promoter, was nearly identical to the endogenous rhodopsin. EGFP was first detected in the ventral nasal retinal in an area of precocious neurogenesis referred to as the "ventral patch". Subsequent expression of EGFP was observed in isolated cells sporadically distributed across the dorsal and central retina. However, confocal microscopy and spatial analysis of larval eyes or retinal explants from adults revealed a precise arrangement to the rod photoreceptors. The rod terminals were arranged in regularly spaced rows with clearly identifiable telodendria linking neighboring cells. The rod inner segments projected through the cone mosaic in a predictable pattern. In the adult, the rod mosaic originated near the retinal margin where clusters of rods differentiated around the immature short single cone. In the embryo, the sporadic differentiation of the rods led to the gradual formation of the mosaic pattern. With the growing interest in neuronal stem cells, revisiting this model of neurogenesis provides an avenue to uncover mechanisms underlying the precise integration of new neuronal elements into a preexisting neural network.
脊椎动物视网膜内神经元的数量和分布受到严格调控。这在硬骨鱼中视锥光感受器高度有序、类似晶体的排列中尤为明显。在本报告中，利用斑马鱼的转基因品系，描述了一种新型的、受发育调控的视杆光感受器镶嵌模式。在非洲爪蟾视紫红质基因启动子的控制下，绿色荧光蛋白（EGFP）的时空表达与内源性视紫红质几乎相同。EGFP首先在腹侧鼻侧视网膜中一个称为“腹侧斑块”的早熟神经发生区域被检测到。随后在零星分布于背侧和中央视网膜的单个细胞中观察到EGFP的表达。然而，共聚焦显微镜检查以及对幼虫眼睛或成体视网膜外植体的空间分析揭示了视杆光感受器的精确排列。视杆终末以规则间隔的行排列，相邻细胞之间有清晰可辨的终末分支相连。视杆内段以可预测的模式穿过视锥镶嵌。在成体中，视杆镶嵌起源于视网膜边缘附近，视杆簇围绕未成熟的短单视锥分化。在胚胎中，视杆的零星分化导致镶嵌模式逐渐形成。随着对神经干细胞的兴趣日益增加，重新审视这个神经发生模型为揭示新的神经元元件精确整合到预先存在的神经网络背后的机制提供了一条途径。
