Eukaryotic stress granules: the ins and outs of translation

Abstract

The stress response in eukaryotic cells often inhibits translation initiation and leads to the formation of cytoplasmic RNA-protein complexes referred to as stress granules. Stress granules contain nontranslating mRNAs, translation initiation components, and many additional proteins affecting mRNA function. Stress granules have been proposed to affect mRNA translation and stability and have been linked to apoptosis and nuclear processes. Stress granules also interact with P-bodies, another cytoplasmic RNP granule containing nontranslating mRNA, translation repressors, and some mRNA degradation machinery. Together, stress granules and P-bodies reveal a dynamic cycle of distinct biochemical and compartmentalized mRNPs in the cytosol, with implications for the control of mRNA function.

Figure 1. A continuum of mRNP granules

Select examples of mRNP granules with compositional similarities to both stress granules and P-bodies: C.elegans blastomere germ granules, Gallo et al, 2008; C.elegans arrested ovulation oocyte foci, Jud et al, 2008; Drosophila neuronal transport granules, Barbee et al, 2006; Dendritic P-body, Cougot et al, 2008. Components observed solely in stress granules are highlighted in red, those solely in P-bodies in green, and those seen in both foci are highlighted in yellow. Lists are not necessarily exhaustive, and with specific experimental manipulation, some P-body/stress granule ‘distinct’ components have been observed in both structures.

Figure 2. Model integrating Stress Granules, and P-bodies, into an mRNP cycle

A speculative model for mRNP transitions, particularly during stress. Dashed arrows indicate possible destination of exported nascent transcripts. Wavy purple lines represent microtubules, and their possible contribution of dynein/kinesin-mediated motorized transport to granule aggregation, and/or movement of mRNPs between different mRNP states.