MRNA localization to P-bodies in yeast is bi-phasic with many mRNAs captured in a late Bfr1p-dependent wave

Clare E Simpson,Christopher J Kershaw,Mark P Ashe,Jennifer Lui,Paul F G Sims

doi:10.1242/jcs.139055

Clare E Simpson, Christopher J Kershaw + Show 3 more

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ABSTRACTThe relocalization of translationally repressed mRNAs to mRNA processing bodies Pbodies is a key consequence of cellular stress across many systems. Pbodies harbor mRNA degradation components and are implicated in mRNA decay, but the relative timing and control of mRNA relocalization to Pbodies is poorly understood. We used the MS2GFP system to follow the movement of specific endogenous mRNAs in live Saccharomyces cerevisiae cells after nutritional stress. It appears that the relocalization of mRNA to Pbodies after stress is biphasic some mRNAs are present early, whereas others are recruited much later concomitant with recruitment of translation initiation factors, such as eIF4E. We also find that Bfr1p is a latephaselocalizing Pbody protein that is important for the delayed entry of certain mRNAS to Pbodies. Therefore, for the mRNAs tested, relocalization to Pbodies varies both in terms of the kinetics and factor requirements. This work highlights a potential new regulatory juncture in gene expression that would facilitate the overall rationalization of protein content required for adaptation to stress.

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Stringent regulation of mRNA translation and degradation is fundamental in allowing eukaryotic cells to control their diverse protein content
We studied the relocalization of the eukaryotic translation initiation factors, eIF4E, eIF4G and Pab1p both to P-bodies and to stress-induced granules (EGPbodies), which contain these select mRNA-associated translation initiation factors but, crucially, lack the components of the mRNA decay machinery that are associated with P-bodies (Hoyle et al, 2007)
Key advantages of this yeast system are that the control elements associated with mRNA transcription and processing [promoters, UTRs, poly(A) sites and terminators] remain intact, as the MS2-binding sites are inserted directly and precisely into the 39UTR of the endogenous gene at its chromosomal locus (Haim et al, 2007)

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Stringent regulation of mRNA translation and degradation is fundamental in allowing eukaryotic cells to control their diverse protein content These mechanisms become especially important following stress; cells must decrease their energy consumption while accumulating proteins that are required for adaptation (Pichon et al, 2012; Simpson and Ashe, 2012). These include stress granules, which are found in many cell types, and neuronal granules and P-granules, which have been found in neurons and embryonic cells, respectively (Thomas et al, 2011; Updike and Strome, 2010) These granules occur in a variety of conditions and they contain many overlapping components, such as mRNAs, mRNA-binding proteins and proteins associated with translation inhibition (Kedersha and Anderson, 2009; Parker and Sheth, 2007). Studies have shown that mRNAs have the ability to re-enter the translational pool following relief from stress (Brengues et al, 2005) and that this ability might be specific to certain mRNAs, occurring over a finite period (Arribere et al, 2011)

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