Article Development of the Fetal Bone Marrow Niche and Regulation of HSC Quiescence and Homing Ability by Emerging Osteolineage Cells Graphical Abstract Highlights Murine fetal long bones have a perfused vasculature beginning at E16.5 HSCs reside within vascularized regions of fetal bone marrow as early as E16.5 The fetal bone marrow vascular niche alone cannot support long-term HSCs Osteolineage cells within fetal bone regulate HSC quiescence and homing ability Authors Su¨ leyman Cosxkun, Hsu Chao, ..., Benoit de Crombrugghe, Karen K. Hirschi Correspondence karen.hirschi@yale.edu In Brief HSCs reside within a specialized niche where interactions with vasculature, oste- oblasts, and stromal components regu- late their self-renewal and differentiation. Cosxkun et al. now map fetal bone marrow niche development and examine the impact of its cellular components on HSC phenotype and function. Cosxkun et al., 2014, Cell Reports 9, 581–590 October 23, 2014 ª2014 The Authors http://dx.doi.org/10.1016/j.celrep.2014.09.013