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Adult hematopoiesis occurs primarily in the bone marrow space where hematopoietic cells interact with stromal niche cells such as osteoblasts. The cover image shows a region of fibrous dysplasia in the bone marrow in the ColI(2.3)⁺/Rs1⁺ transgenic mouse model of increased G_s-GPCR signaling in osteoblastic cells. Interspersed between the thin trabeculae of bone are many fibrous stromal cells, including osteoblasts, and small clusters of hematopoietic cells (center). Our findings indicate that long-term activation of G_s signaling in osteoblastic cells leads to contextual changes in the bone marrow niche that adversely affect HSC maintenance and blood homeostasis. The image is a tiled compilation of photos acquired on a Leica DMI4000B microscope (40× objective, with DMC400 camera) of an H&E section from a femur of a 12-week-old ColI(2.3)⁺/Rs1⁺ mouse. Image by Dr Edward Hsiao. See the article by Schepers et al on page 3425.