Grant: Discovery Grants Program - Individual

During embryonic development, a number of different mechanisms are employed to guide growing axons to their appropriate targets. One such mechanism is chemoattraction, wherein factors are released by the target tissues to attract growing axons. Results from recent work in our lab have identified a small, lipid-soluble vitamin A metabolite, all-trans retinoic acid (RA), as a critical factor in this process in newt spinal cord regeneration. Moreover, we have shown that this molecule has similar effects on outgrowth and directional growth (chemotaxis) on neurons from the pond snail, Lymnaea stagnalis, suggesting some evolutionary conservation in the mechanisms by which developing and regenerating nerves find their targets. In this proposal, we plan to further investigate the role of RA and one of its nuclear receptors, retinoic acid receptor beta (RARb) in spinal cord regeneration in adult newts. Significantly, RARbeta is found in embryonic mouse spinal cords (which can regenerate), but is absent in adult mouse spinal cords (which lose this ability before birth. We have recently isolated and cloned the newt homologue of this receptor. We will determine its temporal and spatial patterns of expression in the regenerating spinal cord in amputated tails. We will also experimentally diminish the expression of this receptor in regenerating adult newt spinal cords by a process called RNA interference, to determine if regeneration is dependent upon its continual expression, as it appears to be in mammalian embryos. These studies will supplement those planned to determine the level of synthesis of endogenous RA in the spinal cords as a consequence of injury as well as those to determine the types of gene products regulated by the receptor in spinal cord cells. Understanding the trauma-induced regeneration processes in the adult newt CNS, as well as identifying the factors required for neuronal outgrowth and directional pathfinding, are important for designing therapeutic strategies to prevent nerve cell degeneration and to restimulate the embryonic pathway in adult mammals, including humans.