Retrograde axonal transport of the GTP-binding protein Gi alpha: a potential neurotrophic intra-axonal messenger.

When a neuronal target is to provide information to the nucleus of the neurone innervating it, it faces the problem of getting its message up the long length of axon separating the cell body from the site of receptor activation at the terminal. The retrograde axonal transport of the neurotrophic molecule, nerve growth factor (NGF), provided one possible mechanism for this information transfer in the sympathetic nervous system. However, some neurotrophic molecules are not retrogradely transported, indicating the message is carried back by a different mechanism. In this paper, we examined such a novel mechanism mediated by the retrograde axonal transport of the alpha subunit of the second messenger protein, Gi. It is proposed that some non-transported neurotrophic molecules may produce a stable second messenger that is itself transported to the nucleus to convey the target derived information for survival.