COMPLEXITY OF IN VIVO AXON GUIDANCE

这个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CNS疾病的可能用途可能取决于这些神经元将轴突发送到适当的靶点。 在发育过程中，轴突生长的路径受到导向机制的调节，导向机制由沿路径沿着不均匀分布的分子线索组成。要实现这一长期目标，有必要详细了解引导线索的梯度如何指导轴突的生长。最近的进展已经导致在识别和演示的3个非扩散梯度分子参与的蟑螂胚胎的腿中的Til先锋轴突的生长的指导的体内功能。这些分子定位于轴突生长的基底，包括基底膜中的2和表皮上皮细胞表面上的1。这些引导线索和生长锥之间的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个功能冗余的线索，并且这些线索可能相互作用。蟑螂胚胎是研究这一发育事件复杂性的理想系统。 它的解剖简单性，使近端生长的确定先锋轴突在腿中观察生活准备。在这个提议中，这些线索中的每一个都将被分子表征，它们在体内和体外引导轴突生长的能力的细节将被检查，它们之间的体内相互作用也将被检查。第四分子分布在梯度沿着轴突生长的路径已被确定，并提出实验来研究其在轴突指导的作用。像许多发育事件一样，轴突导向也可能是遗传保守的。从对这种昆虫的研究中获得的信息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.