Messenger RNA targeting to endoplasmic reticulum stress signalling sites

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Endoplasmic reticulum (ER) stress arises from protein misfolding, activating the unfolded protein response (UPR).
• The UPR is mediated by sensors like Ire1, which splices HAC1 mRNA (yeast) or XBP1 (metazoans) to restore ER homeostasis.
• Translational control of HAC1 mRNA by its intron and 5' UTR regulates Hac1 synthesis.

Purpose of the Study:

• To investigate the molecular mechanism of Ire1 activation and HAC1 mRNA splicing during the UPR.
• To elucidate how Ire1 clustering and mRNA recruitment contribute to UPR signaling.
• To identify the role of conserved elements in HAC1 mRNA targeting.

Main Methods:

• Yeast genetics and molecular biology techniques.
• Analysis of Ire1 oligomerization and localization using microscopy.
• mRNA-protein interaction studies and functional assays.

Main Results:

• Ire1 activation leads to its clustering into discrete ER membrane foci, forming higher-order oligomers.
• Unspliced HAC1 mRNA is recruited to these Ire1 foci via a bipartite element in its 3' UTR.
• Disruption of Ire1 clustering or mRNA recruitment significantly impairs UPR signaling.
• The HAC1 3' UTR element can target other repressed mRNAs to Ire1 foci.

Conclusions:

• mRNA recruitment to Ire1 signaling centers is a novel mechanism for controlling eukaryotic gene expression.
• This process is crucial for efficient UPR activation and cellular adaptation to ER stress.
• The findings reveal a new paradigm in gene expression regulation at the ER membrane.