A single cell atlas defines perinatal factors that drive murine bone marrow development

Processes that direct initial colonization and maturation of the bone marrow remain elusive, despite their importance to lifelong hematopoiesis. Bone marrow mesenchymal and stromal cell (BMSC) maturation must establish supportive hematopoietic niches prior to the recruitment and colonization of hematopoietic stem cells (HSCs). Here, we define the identity of murine BMSC progenitors and temporal nature of marrow colonization through a single cell atlas spanning late gestation through 18 months of age. We define progenitor cells and developmental trajectories for Cxcl12-abundant reticular (CAR) cells and osteoblasts within the marrow, including the emergence of direct and secreted signaling modalities that impact HSC quiescence and regenerative capacity. We further identify temporal changes in Early B Cell Factor (Ebf) 1-3 transcription factor expression and activity that correlate with niche establishment. These transcriptional activities relate to change to changes in systemic physiology, including metabolic, inflammatory, and hypoxic signaling, that direct CAR cell emergence after birth in mice. These findings provide unprecedented resolution to the colonization and maturation of the murine bone marrow environment.