Spatiotemporal regulation of endoplasmic reticulum stress visualized by live imaging of bipA mRNA in Aspergillus oryzae

The molecular mechanisms of the endoplasmic reticulum (ER) stress response have been elucidated in detail in many eukaryotic organisms. However, there is still a lack of cellular biological knowledge about the ER stress response in filamentous fungi. In this study, we utilized the MS2 system to analyze the mRNA of bipA, which encodes a typical ER chaperone expressed in response to dithiothreitol (DTT)-induced ER stress in living cells of Aspergillus oryzae. Fluorescence microscopy revealed the temporal changes in the amount of bipA mRNA in the cell with or without DTT. It was also shown that when ER stress was induced with DTT, bipA mRNA expression was observed from the apical to the basal regions of the hyphal cells. Moreover, although some of the ER stress-induced bipA mRNA showed microtubule-dependent long-distance dynamics, most of it was observed to be static. Furthermore, treatment with cycloheximide, a translation inhibitor, increased the long-range dynamics of bipA mRNA, suggesting that static bipA mRNA is being translated. Collectively, we have clarified the mechanism of gene expression and regulation of intracellular mRNA levels in response to ER stress in the filamentous fungus A. oryzae cells.