Osteocyte regulation of hematopoiesis. Osteocytes imbedded in bone communicate with cells in the bone marrow through canaliculi. Osteocytes are known to produce RANKL, which activates osteoclasts (OCs), and the Wnt antagonist sclerostin, which suppresses osteoblasts (OBs). The present study by Fulzele et al shows that osteocytes also produce G-CSF (and potentially other myelopoiesis-stimulating factors) that results in hematopoietic progenitor cell (HPC) proliferation and increased neutrophil and monocyte production.¹