In the second talk on growth cones and regeneration Gaynor Spencer told us about experiments with acutely isolated axons from Lymnaea stagnalis in cell culture. The talk started out by reviewing the involvement of local protein synthesis in axon regeneration and axon pathfinding. She showed how a neurotransmitter receptor can be synthesized and functionally inserted in axons isolated from the cell soma and hence the nucleus.
An important gene in regeneration appears to be beta-thymosin. Beta-thymosin binds free actin monomers and thereby prevents actin polymerization and is thought to act as an inhibitor of neurites outgrowth. It is the most abundant mRNA in regenerating neurons and dsRNA inhibition of beta-thymosin mRNA enhances outgrowth of transsected neurites. The same dsRNA inhibition disrupts the turning response these neurites show towards dopamine.
She then switched to retinoic acid. It's a vitamin A metabolite and plays a very important role in development and regeneration in vertebrates. In cultured Lymnaea neurons, retinoic acid is a strong chemo-attractant for the growth cones. In contrast to vertebrate work, which shows that retinoic acid works via nuclear receptors, the chemo-attraction from retinoic acid also works in isolated neurites from Lymnaea which of course do not have a nucleus.