Investigation of the origin of the osteoclast by use of transplantation on chick chorioallantoic membrane.

In recent years, it has become generally accepted that osteoblasts and osteoclasts are derived from separate stem cell lines: the osteoblasts from mesenchymal cells, and the osteoclasts from cells of hematopoietic origin. Principal evidence for this belief comes from experimental approaches, such as autoradiography, parabiosis, quail-chick nuclear markers, lysosomal markers in beige mice, and so forth. However, the problem remains unsolved. For further investigation of osteoclast origin, three experimental designs were employed: (1) six-day quail limb buds were directly implanted into chick chorioallantoic membrane; (2) viable or devitalized Dunn osteosarcomas were implanted onto chorioallantoic membrane; and (3) six-day quail limb buds in diffusion chambers were implanted onto chorioallantoic membrane by use of exogenous parathyroid hormone (PTH) stimulation. In these experiments, osteoblasts and osteoclasts were identified from host (chorioallantoic membrane) and implant (quail limb bud). Limb buds within diffusion chambers formed osteoclasts in response to PTH despite no blood circulation or bone marrow formation. These data indicate that the mesenchyme (perichondrium) plays an important role. Either osteoclast mononuclear precursors have migrated from hematopoietic sources to the perichondrium before transplantation of the limb buds or mesenchymal cells of developing bone can form osteoclasts. Thus, the origin of the osteoclasts should still be considered an unsettled question.