Axon guidance at the central nervous system midline

A key feature of the central nervous system of most higher organisms is the ir bilateral symmetry about the midline, The specialised cells that lie at the midline have an essential role in regulating the axon guidance decision s of both neurons that project axons across the midline and those that proj ect on one side. The midline cells produce both attractive and repellent sh ort- and long-range signals to guide axonal growth. The axons themselves ex press specific receptors that can be dynamically regulated in response to m idline-derived signals. In this way, axons extend toward or away from the m idline and those that do cross change their behaviour to respond to longitu dinal signals on the contralateral side.