The cover is a picture of a bunch of grape. Each grain represents stem cells. The color is meant to show the glutathione (GSH) level of stem cells which is stained as green (high GSH level) or red (low GSH level) by FreSHtracer, our real- time GSH fluorescence dye. In this cover image, we’d like to express the heterogeneity of GSH levels in living stem cells in response to environmental stress. The cover image was created by Eui Man Jeong and In-Gyu Kim (see Jeong et al. in this issue, pages 367-379).