mRNA granules focus the production of glycolytic enzymes to fuel glucose fermentation

Abstract

mRNA localisation represents a widespread mechanism to control the translation, stability and overall fate of mRNAs. Following stress, mRNAs are translationally repressed and localise either to P-bodies or stress granules, where they are degraded or stored, respectively. In a recent study from the Ashe lab, it has been shown that two glycolytic mRNAs (PDC1 and ENO2) co-localise to the same discrete multiple cytoplasmic granules in exponentially growing S. cerevisiae, which are not related to P-bodies or stress granules (Lui et al 2014). This raises the question as to whether these granules can serve as a factory for the production of enzymes from the glycolytic pathway or as a way to physiologically optimise the efficiency of the whole metabolic pathway (Lui et al. 2014). In order to explore this idea further, microscopy approaches were utilised to study several mRNAs from the glycolytic pathway in live cells. The studied mRNAs were observed to localise to multiple dynamic cytoplasmic granules per cell and they usually overlap with other transcripts of the pathway. We observed that while a core of essential glycolytic mRNAs tend to co-localise to the same granules, termed core fermentation -CoFe granule, the remaining mRNAs lay to localise to a different class of granule called accessory fermentation -AFe granules, suggesting that coregulation of the production of the glycolytic enzymes might provide a way to regulate the whole pathway. Similarly, using ‘translating RNA imaging by coat protein knock-off’ (TRICK), we found that localisation of glycolytic mRNAs to the granules is linked to active mRNA translation. Moreover, the propensity of glycolytic mRNAs to enter granules varies depending on nutrients, with highly fermentative carbon sources favouring granule localisation. Indeed, the degree of fermentation required by cells seems intrinsically connected to the extent of mRNA localisation to granules. While the molecular composition and the mechanisms by which these granules are assembled remain unknown, some insights of potential trans and cis-acting elements, like the gene promoter or actor of the gene gating hypothesis, offer promising insights into potential molecular pathways that might be involved in their formation and proteins that might form part of the granules. Overall, this work highlights the likelihood that these glycolytic CoFe and AFe mRNA granules serve as a factory for the glycolytic enzymes but also as a way to optimise and/or regulate the pathway physiologically.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Christopher Grant (Supervisor) & Mark Ashe (Supervisor)