Fig. 5
From: Development, functional organization, and evolution of vertebrate axial motor circuits
Developmental mechanisms of axial motor circuit assembly. a Dendritic morphology and premotor input pattern for MN columnar subtypes. MMC neurons have dendrites that extend across the midline and their monosynaptic premotor inputs are distributed across both sides of the spinal cord. Like MMC neurons, HMC neuron dendrites extend medio-laterally and have a similar premotor input distribution pattern. LMC neurons have radially organized dendrites and receive premotor inputs predominantly from ipsilateral spinal interneurons. Darker shading indicates higher density of interneurons connected to MNs. b Effect of Hoxc9 mutation on premotor input pattern. In Hoxc9 mutants, thoracic HMC neurons are converted to LMC fate, while MMC neurons are grossly unaffected. In Hoxc9 mutants, ectopic LMC neurons still project to intercostal muscle. The dendritic pattern of thoracic MNs in Hoxc9 mutants becomes more limb-like, and MNs projecting to intercostal muscle receive a higher distribution of inputs from ipsilateral premotor interneurons. Diagram based on data in [84]