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之间相互建立的精确联系。为了形成这些连接，轴突必须在发育过程中长距离导航到它们的目标区域。无论是长距离的吸引或排斥分子，还是促进选择性黏附的短程信号，都可以引导轴突生长。视觉系统中形成的连接特别耐人寻味，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觉到自己的全球位置。我们对这种位置信息的决定因素的理解还远未完成。一种使用果蝇的遗传方法有可能纯粹根据它们的功能来识别介导轴突引导的新成分。影响果蝇光感受器轴突形成的连接的突变的基因筛查已经启动。该屏幕使用马赛克方法，允许识别发育早期也需要的基因突变。这种筛查也是快速的，有利于分离出具有轴突寻径特有缺陷的突变。已经确定了两个基因的突变，这两个基因控制着特定光感受器的寻路步骤。现在将对这些基因编码的蛋白质进行表征，以了解它们在轴突引导中的功能基础。屏幕还将继续，以获得视觉系统投影模式的遗传要求的更完整的图景。

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.