Morphological specification of trigeminal neurites depends on target fields

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• Primary sensory neurons connect the periphery to the central nervous system (CNS) using two distinct axonal processes.
• The unique morphological patterning of these axonal terminals in their targets is well-established.
• It remains unknown whether this differentiation arises intrinsically from the neuron's cell body or from external cues provided by the target tissue.

Purpose of the Study:

• To investigate the origins of axonal differentiation in primary sensory neurons.
• To determine if target-derived signals or intrinsic neuronal programming dictates the unique morphology of peripheral and central axonal projections.

Main Methods:

• Utilized an embryonic (E15) trigeminal ganglion explant coculture system.
• Manipulated explant orientation (180-degree rotation) and target availability (dual peripheral or central targets).
• Labeled axonal processes using the lipophilic tracer DiI for visualization.

Main Results:

• Trigeminal axons demonstrated the ability to grow into inappropriate targets (central axons into peripheral targets, and vice versa).
• Both axonal processes could simultaneously innervate multiple targets (peripheral and central).
• Axonal differentiation was specific to the target tissue, irrespective of the axon's normal projection.

Conclusions:

• Embryonic sensory neuron axons are not inherently selective for their targets.
• Target-derived signals play a crucial role in dictating the morphological patterning of sensory axonal processes.
• This suggests a model where environmental cues guide neuronal development and connectivity.