Résumé :
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Spinal motoneurons display a remarkable diversity in cell body diameter, axonal trajectories and motor unit size. To study intrinsic and extrinsic factors determining this diversity we developed novel flow cytometry and FACS-based techniques. Here, we FACS-isolated mouse E12.5 axial and hindlimb motoneurons, monitored their gene expression profile and compared their electrical and morphological properties in culture. Hindlimb motor neurons had a high whole cell capacitance indicating a large soma and were responsive to HGF (hepatocyte growth factor), a neurotrophic factor produced in the limb mesenchyme. Hindlimb motoneurons grew long axons with few mostly terminal branches. In contrast, axial motor neurons had a low whole cell capacitance, were unresponsive to HGF and grew short axons with numerous proximal branches. Hb9 over-expression in limb motor neurons forced them to adopt an axonal morphology reminiscent of axial motor neurons suggesting a direct role of Hb9 in axon growth and branching. We conclude that the distinct morphologies of limb and axial motor neurons reflect their respective roles in fine versus bulk movement and their reported differences in motor unit size.
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