The unfolded protein response (UPR) relies on the non-canonical splicing of XBP1 mRNA on the surface of the endoplasmic reticulum (ER). The molecular switch that initiates splicing is the oligomerization of the ER stress sensor and UPR endonuclease IRE1α (inositol-requiring enzyme 1 alpha).
While IRE1α can form large clusters that have been proposed to function as XBP1 processing centers on the ER, the actual oligomeric state of active IRE1α complexes as well as the targeting mechanism that recruits XBP1 to IRE1α oligomers remains unknown.
We have developed a single-molecule imaging approach that can monitor the recruitment of individual XBP1 transcripts to the ER surface, and used it to visualize how IRE1α-catalyzed splicing mobilizes XBP1 mRNA from the ER membrane in response to ER stress. Our current work focuses on quantifying the dynamics of the transient XBP1-IRE1α interactions on the ER surface.