An Importin Code in neuronal transport from synapse-to-nucleus?

INTRODUCTION: The principle cells of the brain- neurons- express more genes than any other cell type. As many rudimentary processes of the brain, such as long-lasting changes in synaptic efficacy, involve alterations to the expression of genes, the characterisation of proteins and processes that influence transcription is a high priority in neuroscience. An emerging system capable of transducing signals that likely influence transcription is synapse-to-nucleus macromolecular protein shuttling, in which synaptic proteins are relayed to the nucleus in a complex with importins (also referred to by their gene name: Karyopherins/KPNs) and molecular motors such as dynein (Jordan and Kreutz, 2009, Figure 1C). Despite a central position in a neuronal process capable of altering transcription, there is a dearth of research into importin function in neurites. In this opinion paper we summarize neuronal importin understanding to date, present novel ideas relating to their neuronal function and highlight the reductionist nature of the classical description of nuclear import with the specific example that complex composition is likely much more intricate than is being considered.