Neurons are particularly refractile to repair when demaged. Therefore, models of axonal regenration are important to unravel the molecular mechanisms of neuronal repair. C. elegans is a powerful model to test genetic factors affecting axonal regeneration, since its axons can regrow upon injury (Mehmet Fatih Yanik et al 2004, Hammarlund et al, 2007). The expression of the
mec-4d mutation causes degeneration of the touch receptor neurons soon after their birth. We previously showed that the TRN neurons in
mec-4d mutants are fully protected in animals that have been in diapause for over a week, (Calixto et al, 2012). By analyzing the TRN morphology and functionality throughout the dauer stage we made the surprising finding that the observed protection is due to complete and functional regeneration of damaged axons during diapause.We found that DAF-2 downregulation and dietary restriction, which occur during diapause are neuroprotective (Calixto et al, 2012) but are not sufficient to produce neuronal regeneration. A key regulator of regeneration is DLK-1 (Dong Yan et al, 2009). To test whether regeneration in dauer required DLK-1, we evaluated axonal degeneration and regrowth in
dlk-1;
mec-4d animals during normal development and in diapause. At 12 hours post hatching neurons are born and begin to degenerate, similar to
mec-4d animals. However, the
dlk-1;
mec-4d axons fail to completely degenerate once they are truncated, and remain truncated at later times during adulthood, consistently with roles of
dlk-1/Wallenda in Drosophila (Miller et al, 2009) Additionally, we observed irregular neurite outgrowth, and defects in pathfinding, at different stages of development, which does not occur in the
dlk-1 mutant alone, where growth and extension are normal after hatching. At the fist day in dauer
dlk-1;
mec-4d mutants displayed an increase in wild-type neurons (30-35%) in contrast to non-dauer conditions at the time of dauer entry (7-9%), which indicates a regenerative effect independent of DLK-1. Full regeneration in dauer however requires DLK-1, for axons do not regrow beyond the initial regeneration. To better understand the gene networks underlying regeneration in dauer, we performed a genetic screen for animals that failed to regenerate the TRNs during diapause. Of the initial 1000 mutants, we found 58 candidates who do not regenerate in dauer and group in three categories: axons that remain protected in absence of regeneration, progressive decline of protection and accelerated axonal death. We believe that the characterization of these mutants will provide novel insight into the genetic factors and metabolic state that promotes axon regeneration during diapause.