title: Epithelial induction of osteogenesis in embryonic chick mandibular mesenchyme: a possible role for basal lamina.
abstract: The initiation of osteogenesis at 7 days in the embryonic chick mandibular mesenchyme depends on an epithelial induction in the mandible to day 4. This article reviews a series of experiments conducted to study the nature of this inductive mechanism. Transfilter tissue recombinations were used to determine whether direct tissue apposition was required for induction. Ultrastructural studies of the epithelial-mesenchymal interface were conducted to see if direct epithelial-mesenchymal cell-cell contacts occurred during the inductive stage in vivo. Epithelial cells were cultured on Millipore filters for 28 days and allowed to deposit extracellular products. These products were tested for inductive activity. Findings from these three sets of experiments were discussed with respect to the inductive mechanism. Our results indicate that the induction is not mediated by a diffusible substance and that direct apposition of the two tissues is required. The mechanism of induction, however, does not require direct epithelial-mesenchymal cell to cell contacts. This suggests that a nondiffusible component of the extracellular matrix may be involved. Epithelial extracellular products are inductively active and have the appearance of basal lamina. The active component of the extracellular product is proteinaceous, perhaps collagen, and appears to be situated in the epithelial basal lamina. The role of basal lamina in epithelial-mesenchymal interactions is discussed.
mesh_terms: D000818:Animals; D001383:Azetidinecarboxylic Acid / Q000494:pharmacology; D001485:Basement Membrane / Q000502:physiology*; D002454:Cell Differentiation; D002642:Chick Embryo; D004627:Embryonic Induction; D004848:Epithelium / Q000502:physiology; D005374:Filtration; D008334:Mandible / Q000196:embryology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D010012:Osteogenesis; D014357:Trypsin / Q000494:pharmacology
chemical_list: D001383:Azetidinecarboxylic Acid; D014357:Trypsin