The mechanism whereby Ca2+ signaling promotes axonal regrowth

The failure of axon regeneration in the fully developed mammalian central nervous system (CNS) is due to the presence of myelin inhibitors and to the low capacity of most CNS neurons to grow their axons. Mollusc neurons represent a novel comparative model to investigate the intrinsic mechanisms which prevent axonal regeneration. They are naturally demyelinated and, after lesion, display either regrowth (Aplysia limacina) or degeneration (Octopus vulgaris). A Ca2+ signal localized at the tip of severed axon may result in the formation of a new growth cone by a yet unclear mechanism. (ii) The present project aims at comparing the Ca2+ signaling toolkit which delivers the Ca2+ signal upon lesion and the Ca2+-sensitive proteins recruited by the Ca2+ pulse in neurons from Aplysia limacina (regenerating) and Octopus vulgaris (non regenerating). Our working hypothesis is that either the Ca2+ pools or the intracellular machinery engaged by axotomy differ in the neurons of the two species. (iii) We will employ electrophysiological, Ca2+ imaging, biochemical, proteomic, molecular biology and electron microscopy techniques to perform a comparative analysis aimed at unravelling the molecule(s) which prevent axonal regeneration. Once the proteins underpinning axonal regrowth in Aplysia are identified, they will be recombinantly expressed and microinjected into Octopus neurons to assess whether they can induce axonal regeneration also in this cell type. (iv) This study will reveal putative targets to devise novel specific treatments to be delivered selectively in the very early phase after an axonal lesion in order to rescue nerve fibres from degeneration.