Developmental stages of osteoclast lineage. Osteoclasts are derived from hematopoietic precursor cells, and belong to the monocytes/macrophages lineage. With response to macrophage-colony stimulating factor (M-CSF), hematopoietic stem cells undergo differentiation into the granulocyte macrophage colony forming units (CFU-GM), which are the common precursor cells of granulocytes, macrophages, and osteoclasts. CFU-GM-derived cells differentiate to form mononuclear preosteoclast, which fuse together to subsequently form multinucleated osteoclasts.