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Induction of bone by epithelial cell products.

The bones of the head and face of vertebrate embryos only form after their progenitor cells have undergone an inductive interaction with embryonic epithelia. We have investigated whether epithelial cell products can substitute for epithelia in allowing mandibular ectomesenchyme to form bone. Mandibular epithelia from embryonic chicks were cultured on Millipore filters for 28 days to allow them to deposit an extracellular matrix, shown by electron microscopy to be a basal lamina-like material. Mandibular ectomesenchymal cells formed bone when placed on to these epithelial extracellular products and grafted to chorioallantoic membranes of host embryos. Treatment of epithelial cultures with trypsin or L-azetidine-carboxylic acid removed both the extracellular products and their ability to induce bone formation. Hyaluronidase treatment did neither. We concluded that a proteinaceous component of epithelial basal lamina provides a sufficient inductive stimulus to initiate differentiation of bone within mandibular ectomesenchyme.