Many mature central nervous system (CNS) neurons in non-mammals, such as C. elegans, Drosophila, and zebrafish, are able to regenerate after injuries. The MAPK cascade, DLK-1/MKK-4/PMK-3/MAK2, is identified as an essential signaling pathway involved in axon regeneration in C. elegans. Calcium influx, which is triggered by axotomy, is implicated in DLK-1 activation. Another MAP kinase pathway, MLK-1/MEK-1/KGB-1, acts in parallel with the DLK-1 pathway to control growth-cone formation after axotomy. SVH-1, a homolog of the mammalian hepatocyte growth factor and its receptor SVH-2 function upstream of the MLK-1 pathway to promote axon regeneration. There are also inhibitors of regeneration, such as lin-12/Notch and efa-6. It is possible that the C. elegans pathways that inhibit regeneration function to stabilize the mature, uninjured nervous system.