In summary, we have presented a broad overview of the process of axon guidance, describing the fundamental tenets of axonal navigation shared by disparate species, as well as giving an insight into how different evolutionary advances, such as the development of more complex brains, has been accomplished using a limited suite of axon guidance cues. The growth cone, the tip of the growing axons, is the key structure in sensing and integrating the information provided by guidance cues within the environment. We have discussed some historical axon-pathfinding concepts and experimental techniques that provide insight in both the identification of guidance molecules and mechanisms. Two extensively studied model systems, the retinotectal projection and the midline choice point, have been used to identify the guidance cues and to study the mechanisms of attraction and repulsion induced by them. Finally, several mechanisms modulate the axonal responses at different levels of the signaling pathways, including receptor silencing, protein synthesis, degradation, and endocytosis. In the long term, understanding the mechanisms that underlie axon pathfinding during development will surely help us to determine the basis of many human syndromes with neurological deficits, and perhaps help us to elucidate the cause of neurodegenerative disorders. Encouragingly, studies of neural development have indeed begun to provide insight into neurological diseases and may eventually culminate in strategies for restoring neural connectivity following injury.
Was this article helpful?