New fluorescent reporting system illuminates accumulation of unfolded proteins in endoplasmic reticulum

The endoplasmic reticulum (ER) is a major organelle responsible for protein folding and trafficking. Protein folding stress in the ER can lead to the accumulation of unfolded or misfolded proteins, known as ER stress, which activates the unfolded protein response (UPR). However, UPR can also be activated in the absence of ER stress. Deciphering the complex relationship between ER stress and UPR is critical to understanding cellular stress responses in physiological and pathological conditions.