The study investigates the role of osteoblastic cells in regulating hematopoietic stem cell (HSC) niche and function. Mice with osteoblast-specific, activated PTH/PTHrP receptors (PPR) were used to assess the impact of PPR activation on HSCs. The results show that PPR-stimulated osteoblastic cells produce high levels of the Notch ligand Jagged 1, which supports an increase in HSC numbers and activates Notch1 signaling in vivo. Parathyroid hormone (PTH) administration increased the number of osteoblasts and primitive HSCs, and improved survival after bone marrow transplantation. These findings suggest that osteoblastic cells are a regulatory component of the HSC niche, influencing stem cell function through Notch activation. The study also highlights the potential for pharmacological manipulation of the bone marrow microenvironment to expand HSCs and improve engraftment outcomes.The study investigates the role of osteoblastic cells in regulating hematopoietic stem cell (HSC) niche and function. Mice with osteoblast-specific, activated PTH/PTHrP receptors (PPR) were used to assess the impact of PPR activation on HSCs. The results show that PPR-stimulated osteoblastic cells produce high levels of the Notch ligand Jagged 1, which supports an increase in HSC numbers and activates Notch1 signaling in vivo. Parathyroid hormone (PTH) administration increased the number of osteoblasts and primitive HSCs, and improved survival after bone marrow transplantation. These findings suggest that osteoblastic cells are a regulatory component of the HSC niche, influencing stem cell function through Notch activation. The study also highlights the potential for pharmacological manipulation of the bone marrow microenvironment to expand HSCs and improve engraftment outcomes.