in-vivo-assessment-microtubule-dynamics-orientation-caenorhabditis

<em>In vivo</em> Assessment of Microtubule Dynamics and Orientation in <em>Caenorhabditis elegans</em> Neurons

In neurons, microtubule orientation has been a key assessor to identify axons that have plus-end out microtubules and dendrites that generally have mixed ...

DBT-National Brain Research Centre

Neuronal injury often leads to devastating consequences such as loss of senses or locomotion. Restoration of function after injury relies on whether the injured axons can find their target cells. Although fusion between injured proximal axon and distal fragment has been observed in many organisms, its functional significance is not clear. Here, using  mechanosensory neurons, we address this question. Using two femtosecond lasers simultaneously, we could scan and sever posterior lateral microtubule neurons [posterior lateral microtubules (PLMs)] on both sides of the worm. We showed that axotomy of both PLMs leads to a dramatic loss of posterior touch sensation. During the regenerative phase, only axons that fuse to their distal counterparts contribute to functional recovery. Loss of  miRNA promotes functional restoration in both larval and adult stages. In the L4 stage, loss of  increases fusion events by increasing the mRNA level of one of the cell-recognition molecules, CED-7. The ability to establish cytoplasmic continuity between the proximal and distal ends declines with age. Loss of  overcomes this barrier by promoting axonal transport and enrichment of the EFF-1 fusogen at the growing tip of cut processes. Our data reveal the functional property of a regenerating neuron.

 miRNA controls CED-7 homotypic adhesion and EFF-1-mediated axonal self-fusion to restore touch sensation following injury.

Restoration of lost function following a nervous system injury is limited in adulthood as the regenerative capacity of nervous system declines with age. Pharmacological approaches have not been very successful in alleviating the consequences of nervous system injury. On the contrary, physical activity and rehabilitation interventions are often beneficial to improve the health conditions in the patients with neuronal injuries. Using touch neuron circuit of , we investigated the role of physical exercise in the improvement of functional restoration after axotomy. We found that a swimming session of 90 min following the axotomy of posterior lateral microtubule (PLM) neuron can improve functional recovery in larval and adult stage animals. In older age, multiple exercise sessions were required to enhance the functional recovery. Genetic analysis of axon regeneration mutants showed that exercise-mediated enhancement of functional recovery depends on the ability of axon to regenerate. Exercise promotes early initiation of regrowth, self-fusion of proximal and distal ends, as well as postregrowth enhancement of function. We further found that the swimming exercise promotes axon regeneration through the activity of cellular energy sensor AAK-2/AMPK in both muscle and neuron. Our study established a paradigm where systemic effects of exercise on functional regeneration could be addressed at the single neuron level.

Anindya Ghosh-Roy

DBT-National Brain Research Centre

In vivo Assessment of Microtubule Dynamics and Orientation in Caenorhabditis elegans Neurons