Axon Guidance in the Drosophila Visual System

神经系统内信息的准确传递依赖于神经元彼此之间的精确连接。为了形成这些连接，轴突在发育过程中必须经过很长的距离才能到达它们的目标区域。远程吸引或排斥分子和促进选择性粘附的短程信号都可以引导轴突的生长。视觉系统中形成的连接特别有趣，因为它们导致了视网膜到大脑的精确映射，这表明每个细胞都能感知到自己的全局位置。我们对这个位置信息的行列式的理解还远远不够。一种利用果蝇的遗传方法有可能识别出介导轴突引导的新成分，纯粹基于它们的功能。在果蝇中，对影响光感受器轴突形成的连接的突变的基因筛选已经开始。该筛检采用了一种镶嵌方法，可以识别在发育早期也需要的基因突变。这种筛选也是快速的，并且有利于分离具有轴突寻路特异性缺陷的突变。两个基因的突变控制着一个特定的光感受器的寻路步骤。由这些基因编码的蛋白质现在将被表征，以便了解它们在轴突引导中的功能基础。屏幕也将继续获得视觉系统投影模式的遗传要求的更完整的图片。

Treisman9982093The accurate transmission of information within the nervous system depends on the precise connections that neurons make with each other. To form these connections, axons must navigate over long distances to their target regions during development. Both long-range attractive or repulsive molecules, and short-range cues promoting selective adhesion, can guide axon outgrowth. The connections formed in the visual system are particularly intriguing, as they result in a precise mapping of the retina onto the brain, suggesting that each cell can sense its global position. Our understanding of the determinants of this positional information is far from complete. A genetic approach using the fruit fly Drosophila has the potential to identify new components mediating axon guidance, purely on the basis of their function. A genetic screen for mutations affecting the connections formed by photoreceptor axons in Drosophila has been initiated. The screen uses a mosaic approach that allows the identification of mutations in genes that are also required earlier in development. This screen is also rapid and favors the isolation of mutations that have defects specific to axon pathfinding. Mutations in two genes that control a pathfinding step specific to a particular photoreceptor have been identified. The proteins encoded by these genes will now be characterized in order to understand the basis for their functions in axon guidance. The screen will also be continued to obtain a more complete picture of the genetic requirements for the visual system projection pattern.