A Model for Axon Navigation Based on Glycocodes in the Primary Olfactory System

Abstract

A major question in developmental neurobiology concerns understanding the molecular and cellular mechanisms underlying axon growth and guidance in the developing nervous system. Deciphering the complex interplay of molecular signals responsible for establishing axon and nerve pathways is essential for any effective therapeutic approach to regeneration and repair of injured nervous systems. While many molecules have been shown both in vitro and in vivo to participate in growth cone navigation there is no pathway in the mammalian nervous system for which we understand the principal mechanisms driving the establishment of axon pathways from neuron of origin to target cell. The primary olfactory system is one region that demands particular attention due to it peculiar regenerative capacity. It is the only region in the mammalian nervous system that exhibits continual neuronal turnover and axon growth and guidance throughout embryonic development as well as adult life. Understanding the unique characteristics of axon navigation in this system should provide insight into why the rest of the nervous system is so refractory to regeneration and repair. We present here a model for axon navigation based on the use of cell surface glycocodes for the sorting and selective fasciculation of primary olfactory axons in the nerve fiber layer of the olfactory bulb.