24 Localized Translation through Messenger RNA Localization

Abstract

The establishment of cellular asymmetries and the functions of polarized cells depend on the asymmetric distribution of cytoplasmic proteins. Messenger RNA (mRNA) localization provides an important mechanism for generating asymmetric protein distributions by targeting the synthesis of cytoplasmic proteins to specific subcellular domains. Polarized cellular functions like motility in fibroblasts and synaptic plasticity in dendrites, asymmetric division of budding yeast, and embryonic axis formation in Xenopus and Drosophila all require proteins that are synthesized from localized mRNAs. Furthermore, mRNA localization and translation are often tightly coupled, such that protein synthesis is restricted to the target destination. This spatial control of protein synthesis afforded by mRNA localization provides advantages over direct protein targeting, allowing rapid responses to local requirements. Moreover, localized mRNA translation prevents untoward effects due to premature or ectopic protein function and ensures spatial control of protein concentrations needed for the coordinated assembly and maintenance of multifunctional protein complexes. mRNA transport is facilitated by the packaging of mRNAs into large ribonucleoprotein (RNP) particles or granules, which may also function to silence translation during transport. Recent evidence indicates that localized mRNAs are first “marked” in the nucleus, prior to their export, and in some cases this nuclear marking appears to be necessary for translational repression during transport. Factors that regulate localization and translation are frequently shared among mRNAs within a particular cell type, and an increasing number appear to have evolutionarily conserved functions. Here we review the relationship between mRNA localization and localized translation in representative experimental systems, focusing on...