Influence of epithelial‐mesenchymal interaction on the viability of facial mesenchyme in vitro

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Abstract
Separation and recombination experiments, employing a variety of tissue configurations in organ culture, were performed to determine the extent to which the epithelium of the maxillary process influences the viability of the underlying mesenchyme during organogenesis. The results of these studies indicated that the viability of mesenchyme of the maxillary process of early stage embryos was severely impaired when separated from the overlying epithelium. The influence of epithelium on the viability of mesenchyme was stage dependent; that is, the requirement for the presence of epithelium for the maintenance of the viability of mesenchyme became progressively less pronounced at older developmental stages. The response of mesenchyme to the presence of recombined epithelium resulted in the appearance of a delimited zone of influence extending, within specific boundaries, from the epithelial‐mesenchymal interface. Preliminary data from homotypic (maxillary epithelium‐maxillary mesenchyme), heterotypic (limb apical ectodermal ridge—maxillary mesenchyme) and heterochronic (stage 28 epithelium‐stage 22 mesenchyme) recombination experiments indicated that viability of mesenchyme could be achieved only through direct epithelial‐mesenchymal contact which allowed restoration of normal morphological relationships at the interface of the two tissues.