Keeping tabs on ER stress In the endoplasmic reticulum (ER), oligomerization is a central step in modulating signaling during the unfolded protein response. Tran et al . visualized the active, oligomeric form of the ER stress sensor IRE1α residing in an ER subdomain in stressed human cells. This ER region was composed of narrow (diameter about 28 nanometers) anastomosing ER tubes with a high degree of branching and was continuous with surrounding ER structures. Within the lumen of these narrow IRE1α subdomain tubes, regular protein densities were observed, consistent with ordered oligomers of the lumenal stress–sensing domain of IRE1α. This arrangement may suggest a positive feedback mechanism involved in signaling by IRE1α. —SMH