Identification of a functional mononuclear precursor of the osteoclast in chicken medullary bone marrow cultures

Mononuclear cells were isolated from the peritrabecular bone marrow from the medullary bone of laying hens maintained on a calcium-deficient diet for 1 week. These cells were cultured for up to 7 days on devitalized bovine bone slices after removing the nonadherent fraction. The mononuclear precursors of the osteoclast that are present in such cultures adhere to bone matrix. These cells are TRAP+, express the vitronectin receptor at high levels, and also express high levels of sodium pumps and of carbonic anhydrase, enzymes that are characteristically enriched in the mature osteoclast. Finally, the most mature mononuclear precursors were found to be capable of resorbing the extracellular bone matrix before forming multinucleated osteoclasts.