COMPLEXITY OF IN VIVO AXON GUIDANCE

该项目的长期目标是学习如何在体内操纵轴突生长。在许多情况下，这将是神经系统损伤后治疗的重要组成部分。此外，移植神经元治疗各种中枢神经系统疾病的可能性可能取决于这些神经元将轴突发送到适当的靶点。生长轴突在发育过程中遵循的路径是由沿着路径不均匀分布的分子线索组成的引导机制调节的。已经提出了吸引和排斥引导线索的梯度的特殊作用。为了实现这一长期目标，详细了解引导信号的梯度如何指导轴突的生长是必要的。最近的进展导致鉴定和证明了3个非扩散梯度分子参与引导蟑螂胚胎腿部Til先驱轴突生长的体内功能。这些分子定位于轴突生长的底物，包括2个在基底膜上，1个在表皮上皮细胞表面。这些指导线索和增长锥之间相互作用的复杂性比预期的要大。这种复杂性表现为存在多种功能冗余的线索，并且这些线索可能相互作用。蟑螂胚胎是研究这一发育过程复杂性的理想系统。其解剖的简单性使在活体准备中观察到的腿中已确定的先锋轴突的近端生长。在这个建议中，这些线索将被分子表征，它们在体内和体外引导轴突生长的能力的细节将被检查，以及它们之间在体内的相互作用。第四种分子沿着轴突生长的路径沿梯度分布，并提出了实验来研究其在轴突引导中的作用。像许多发育事件一样，轴突引导也可能在系统发育上保守。从这种昆虫的研究中获得的信息很可能与理解哺乳动物的这些过程非常相关。

The long-term goal of this project is to learn how to manipulate axon growth in vivo. There are many instances when this would be an essential part of a therapeutic treatment after injury to the nervous system. In addition, the possible use of transplanted neurons to treat various CNS diseases may depend on these neurons sending axons to appropriate targets. The path growing axons follow during development is regulated by guidance mechanisms consisting of molecular cues that are non- uniformly distributed along the path. A particular role for gradients of attracting and repelling guidance cues has been proposed. A detailed understanding of how gradients of guidance cues direct the growth of axons is necessary to achieve this long-term goal. Recent progress has resulted in the identification and demonstration of in vivo function of 3 non-diffusible gradient molecules involved in the guidance of growth of the Til pioneer axons in the legs of the cockroach embryo. These molecules, localized to the substrate over which the axons grow, include 2 in the basement membrane and l on the surface of the epidermal epithelial cells. The complexity of the interactions between these guidance cues and the growth cone is greater than had been expected. This complexity is expressed in the fact that multiple and functionally redundant cues exist and in that these cues may interact with one another. The cockroach embryo is an ideal system in which to study the complexity of this developmental event. Its anatomical simplicity enables the proximal growth of identified pioneer axons in the leg to be observed in living preparations. In this proposal each of these cues will be molecularly characterized, the details of their ability to guide axon growth both in vivo and in vitro will be examined, as will be the in vivo interactions among them. A fourth molecule distributed in a gradient along the path of axon growth has been identified and experiments are proposed to examine its role in axon guidance. Like many developmental events, axon guidance is also likely to be phylogenetically conserved. The information obtained from studies of this insect are likely to be very relevant to understanding these processes in mammals.