A dorsal root ganglion neuron (green) with a stem axon that splits into a peripheral and a central-like axon, surrounded by the cell nuclei of DRG glial cells (blue). Image credit: Costa et al. 2025 (CC BY 4.0)
When nerves in our body are damaged, their ability to repair themselves depends on where they are. Some nerves, like those in the arms and legs, can heal, while the ones in the spinal cord cannot. This difference is particularly striking in dorsal root ganglion (DRG) neurons, which have a unique structure. Unlike other neurons, which transmit signals along a single long projection called an axon, DRG neurons branch into two axons – one connecting to the body and the other to the spinal cord. While the branch leading to the body can heal, the one connecting to the spinal cord is unable to regenerate.
It is not clear how DRG neurons develop axons with these differing abilities. Researchers have found that an injury to the body side branch, known as the peripheral axon, can stimulate regrowth in the stretch leading to the spinal cord, known as the central axon. The damage increases the transport of molecules along both axons, boosting the repair of the whole neuron. This suggests that microtubules, the internal highways for transporting materials through cells, may contribute to the difference between the regenerative ability of the two axons of the DRG neuron.
To explore this, Costa et al. studied DRG neurons grown in the laboratory and rodents. Powerful microscopes revealed that the central axons contain more actively growing microtubules than the peripheral axons. However, when the peripheral axon was damaged, the central axon reduced microtubule growth, making it more capable of regeneration. Costa et al. also identified that injury caused changes in levels of microtubule-associated proteins (MAPs), which regulate microtubule behaviour. Reducing the amount of one of these MAPs prevented axon repair in both cell cultures and animal models.
These findings help explain why some nerve fibres regenerate while others do not, highlighting the role of microtubules in this process. Further research is needed to determine whether targeting MAPs may lead to new treatments for spinal cord injury or other nervous system damage in humans.
