Skeletal development and formation of osteoclast-like cells from in situ progenitors in fetal mouse metatarsals cultured in chemically defined medium.

An in vitro model system is described, using metatarsal explants from 15-day mouse embryos (E15) cultured in serumless chemically defined medium, to study fetal skeletal development with particular emphasis on de novo osteoclast formation. The normal pattern of growth and differentiation observed in vitro, assessed by ultrastructure and morphometry, demonstrate a permissive local environment which replicates physiologic temporal and spatial relationships which exist in vivo. The population of committed osteoclast progenitors present in E15 metatarsals form osteoclasts and precursors which have cytochemical and ultrastructural features, as well as kinetics of formation, that are similar to that which occurs in vivo. The responsiveness of osteoclast formation to the effects of added 1,25(OH)2D3 illustrates that controlled manipulation enables one to exploit the system for investigating the role of cytokines, growth factors and osteotropic hormones in skeletal development and osteoclast ontogeny.