Messenger RNA on the move: implications for cell polarity

RNA sorting is an evolutionarily conserved mechanism for establishing asymm etries within a given cell concerning the macromolecular equiptment of defi ned domains. mRNAs as well as cion-coding transcripts are delivered to spec ific subcellular compartments in diverse organisms including developmental systems of Drosophila, Xenopus. ascidiens, zebrafish and echinoderms and in differentiated cells from yeast to mammals. The composition of the RNA loc alization machinery is complex. Both sequence- or structural motifs within RNA molecules to be transported (Lis-acting elements) and various proteins (trans-acting factors) contribute to the localization procedure. Most often these macromolecular ribonucleoprotein complexes exhibit a granular appear ance, and granule localization depends on intact microfilaments or microtub ules. When delivered to their ultimate destinations mRNAs are anchored to a wait translational activation at the appropriate timepoint. Beyond doubt, R NA localization plays a pivotal role in embryonic development, where mRNA m islocations cause severe body pattern defects. In terminally differentiated vertebrate cells RNA transport and local on-site translation presumably ha ve an impact on various cellular functions such as cell motility, myeliniza tion of nerve cell axons and nerve cell communications in the central and p eripheral nervous system. (C) 2001 Elsevier Science Ltd. All rights reserve d.