Guidance of Developing Motor Neurons into the Periphery
Motor neurons (MNs) are a diverse class of cells that originate in the central nervous system and project to muscles in the periphery. The development of all MNs subtypes begins with Sonic Hedgehog (Shh) signaling in the spinal cord and then progresses to increasingly specific guidance signaling systems. MN subtypes are classified by the combined activities of transcription factors and molecular signaling systems that determine axon trajectory. Molecular cues have been attributed to the organization of MNs into columns within the spinal cord and then into specific motor pools. These cues have also been shown to be responsible for axon guidance into the periphery and important for axons to innervate the correct targets. Despite advances in research on specific guidance cues used by different subdivisions of MNs, it is still not fully understood how signaling systems work with one another in the same environment to guide different classes of MNs to their respective muscle targets.
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