An osteo-inductive bone matrix extract stimulates the in vitro conversion of mesenchyme into chondrocytes

Urea and guanidine extracts of demineralized beef and rabbit bone matrix were assayed both in vivo and in vitro. One month following intramuscular implantation into mouse thighs, these extracts induced ectopic cartilage and bone. Seven days following continuous in vitro exposure to the same extracts, stage 24 chick limb bud mesenchymal cells in cultures had differentiated into greater numbers of chondrocytes than controls. These results suggest the feasibility of using limb bud mesenchymal cell cultures as an in vitro assay for bone matrix derived, extractable bioactive factors which effect the conversion of mesenchymal cells into chondrocytes as a requisite step in in vivo osteogenesis.