The role of translational silencing complexes and mRNA degradation factors in RNA localization in flies and mammals (RNA localization and degradation)

Translational control of localized mRNAs is a common mechanism for regulating protein expression in specific cellular subdomains and plays an important role in axes formation, asymmetric cell division, cell motility, and neuronal synaptic plasticity. Localized mRNAs are usually transported in ribonucleoprotein particles and thought to be translationally repressed until the RNA reaches its final destination. It has recently emerged that mRNA degradation factors also play an essential role in mRNA localization. Furthermore, oskar mRNA localization is disrupted by mutations in RISC components. Finally, there is evidence that not only RNA degradation but also translational silencing is coupled to RNA transport in mammals, since non-coding RNAs, such as microRNAs and longer regulatory RNAs, e.g. BC1, can repress translation of mRNAs during transport. It has been postulated that this miRNA-guided silencing occurs in another class of RNPs, called processing bodies, which are the major sites of mRNA degradation in both invertebrate and vertebrate cells. This raises the question of whether P-bodies provide a platform for the transport of translationally repressed RNAs, and function as centers that co-ordinate degradation, translation and localization.