Subcellular RNA compartmentalization

The phenomenon of mRNA sorting to defined subcellular domains is observed i n diverse organisms such as yeast and man. It is now becoming increasingly clear that specific transport of mRNAs to extrasomal locations in nerve cel ls of the central and peripheral nervous system may play an important role in nerve cell development and synaptic plasticity. Although the majority of mRNAs that are expressed in a given neuron are con fined to the cell somata, some transcript species are specifically delivere d to dendrites and/or, albeit less frequently, to the axonal domain. The physiological role and th molecular mechanisms of mRNA compartmentaliza tion is now being investigated extensively. Even though most of the fundame ntal aspects await to be fully characterized; a few interesting data are em erging. In particular, there are a number of different subcellular distribu tion patterns of different RNA species in a given neuronal cell type and RN A compartmentalization may differ depending on the electrical activity of n erve cells. Furthermore, RNA transport is different in neurons of different development al stages. Considerable evidence is now accumulating that mRNA sorting, at least to dendrites and the initial axonal segment, enables local synthesis of key proteins that are detrimental for synaptic function, nerve cell deve lopment and the establishment and maintenance of nerve cell polarity. The molecular determinants specifying mRNA compartmentalization to defined microdomains of nerve cells are just beginning to be unravelled. Targeting appears to be determined by sequence elements residing in the mRNA molecule to which proteins bind in a manner to direct these transcripts along cytos keletal components to their site of function where they may be anchored to await transcriptional activation upon demand. (C) 1999 Elsevier Science Ltd . All rights reserved.