Adventitial reticular cell as the central organizer of the hematopoietic microenvironment/niche. The in situ counterpart of the BM CFU-F (also known as an osteoprogenitor, skeletal stem cell, or mesenchymal stem cell), ARCs, direct formation of cavities through regulation of osteoclastogenesis; contribute to the development of sinusoids, with which they associate; interact with HSC and other hematopoietic cells; and generate osteoblasts and adipocytes, which in turn embody different functional cues for HSCs. ARCs thus integrate the regulation of hematopoiesis with the local, hormonal, and neural control of skeletal growth, remodeling, and circulation.