Lateral motor column axons execute a ternary trajectory choice between limb and body tissues

Area of Science:

• Neuroscience
• Developmental Biology
• Motor Neuron Development

Background:

• Neuronal topographic map formation depends on precise axonal pathfinding.
• Lateral motor column (LMC) axons are believed to exclusively innervate limb targets.
• The guidance mechanisms for motor axons targeting non-limb tissues are not well understood.

Purpose of the Study:

• To investigate the origin of motor nerves innervating ventral flank tissues.
• To elucidate the cellular logic governing motor axon trajectory choices.
• To redefine the innervation targets of the lateral motor column.

Main Methods:

• Tracing motor axon trajectories from the spinal cord.
• Analysis of conditional BmprIa mutants to alter hindlimb mesenchyme identity.
• Histological examination of hindlimb innervation patterns.

Main Results:

• A subset of medial LMC axons unexpectedly innervates ventral non-limb mesenchyme.
• In BmprIa mutants, medial LMC axons are redirected to the ventral flank, and lateral LMC axons innervate bidorsal limbs.
• Medial LMC neurons innervate both ventral flank and limb targets.

Conclusions:

• The lateral motor column (LMC) innervates both limb and body wall tissues.
• LMC axons make a ternary choice (flank, ventral limb, dorsal limb) at the limb base.
• Medial and lateral LMC axons display asymmetric preferences for these trajectories, redefining LMC function.