Chapter 8 Cell adhesion/recognition molecule-mediated steps during the guidance of commissural and motor axons

Abstract

Publisher Summary Accurate pathfinding in both vertebrates and invertebrates clearly involves multiple mechanisms and a large number of molecules, attractive as well as inhibitory. Despite this complexity, the examples of commissural and motoneuron pathfinding described in this chapter show that selective modification of specific molecules within the context of the developing embryo can yield important insights into the mechanisms of guidance and into the roles played by individual molecules. The chapter discusses utilizing the accessibility of the chick embryo to inject specific blocking antibodies or enzymes to alter the function of one or more cell adhesion/recognition molecules and to then determine the effect on neuronal pathfinding. First, results are presented, which show that an interaction between axonin- l/TAG- 1 on the commissural growth cone and neuronal cell adhesion molecules (Nr-CAM/Bravo) on the floor plate is required to guide these axons across the midline. Then evidence is given showing that polysialic acid on neural cell adhesion molecule (NCAM) is required for the correct targeting of motoneurons to specific muscles. These observations can then be used to direct cell culture experiments in which the hypothesized roles can be further refined and tested.