Kainz Pamela M, Adolph Alan R, Wong Kwoon Y, Dowling John E
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138.
J Comp Neurol. 2003 Aug 25;463(3):265-80. doi: 10.1002/cne.10763.
A behavioral assay based on the optokinetic reflex was used to screen chemically mutagenized zebrafish larvae for deficits in visual function. A homozygous recessive mutation, lazy eyes (lze), was isolated based on the observation that 5-day postfertilization (dpf) mutants displayed weaker and less frequent eye movements than wild-type fish in response to moving stripes. Electroretinographic (ERG) recordings revealed that mutants had severely reduced a- and b-wave amplitudes relative to wild-type fish, indicating outer retinal dysfunction. Retinal lamination and cellular differentiation were normal in the lze retina; however, mutant photoreceptor cells had small outer segments and pyknotic nuclei were occasionally observed in the outer retina and the marginal zone of lze. Cone, rod, amacrine, bipolar, and Müller cell marker analyses indicated that the typical lze retina contained fewer rod photoreceptors and fewer Müller cells than wild-type fish at 5 dpf. At 3 dpf, however, mutant retinas had normal numbers of rod photoreceptors and Müller cells, suggesting that the initial differentiation of these cell types occurred normally. Rod photoreceptor histology was normal at this early stage, but Müller cells were often hypertrophied, suggesting that they were unhealthy. Constant light rearing of mutant animals accelerated the Müller cell degeneration, severely worsened the visual deficit, but had no obvious affect on the photoreceptors. When ERG responses and Müller cell degeneration from the same mutant animals were analyzed, the extent of the Müller cell loss matched closely the degree to which ERG responses were reduced. In summary, the lze gene appears to be required for Müller cell viability and normal visual function. The lze mutant may be a model for the study of the involvement of Müller cells in photoreceptor development and function.
基于视动反射的行为学检测方法被用于筛选经化学诱变的斑马鱼幼体的视觉功能缺陷。基于受精后5天（dpf）的突变体相对于野生型鱼在对移动条纹的反应中表现出更弱且频率更低的眼球运动这一观察结果，分离出了一个纯合隐性突变体——lazy eyes（lze）。视网膜电图（ERG）记录显示，相对于野生型鱼，突变体的a波和b波振幅严重降低，表明外层视网膜功能障碍。lze视网膜的视网膜分层和细胞分化正常；然而，突变体光感受器细胞的外节较小，并且在外层视网膜和lze的边缘区偶尔观察到固缩核。视锥细胞、视杆细胞、无长突细胞、双极细胞和米勒细胞标记分析表明，在5 dpf时，典型的lze视网膜中的视杆光感受器和米勒细胞比野生型鱼少。然而，在3 dpf时，突变体视网膜中的视杆光感受器和米勒细胞数量正常，这表明这些细胞类型的初始分化正常发生。在这个早期阶段，视杆光感受器的组织学正常，但米勒细胞经常肥大，表明它们不健康。对突变动物进行持续光照饲养加速了米勒细胞的退化，严重恶化了视觉缺陷，但对光感受器没有明显影响。当分析同一突变动物的ERG反应和米勒细胞退化情况时，米勒细胞损失的程度与ERG反应降低的程度密切匹配。总之，lze基因似乎是米勒细胞存活和正常视觉功能所必需的。lze突变体可能是研究米勒细胞在光感受器发育和功能中的作用的一个模型。
