Dependence of Epithelial Morphogenesis on Extracellular Acid Mucopolysaccharide (MPS)

Abstract

The control of morphogenesis is poorly understood, but may involve extracellular substances associated with cell surfaces (e.g. collagen, MPS). Epitheliomesenchymal interactions provide a system for investigating the role of extracellular materials in organogenesis. Since epithelial morphogenesis is not exclusively dependent upon collagen [BERNFIELD, Dev. Biol., in press, 1970], the localization and morphogenetic significance of MPS was studied. The embryonic salivary epithelial-mesenchymal interface contains MPS as shown by (1) specific staining (Alcian blue at various Mg++ concentrations and Schiff reactivity after two-step periodate oxidation), (2) autoradiography (3H-glucosamine and 35SO4) and (3) removal of stain and radioactivity with MPSase. The MPS is localized almost exclusively at the surface of the growing and branching adenomeres. The role of MPS in epithelial morphogenesis was studied by autoradiography and organ culture after treating the rudiments with various enzymes (collagenases, proteases, sialidases and MPSases) to remove mesenchyme and MPS. Untreated rudiments undergo progressive branching and characteristic epithelial morphogenesis in organ culture. Single-step removal of mesenchyme and surface-associated MPS, followed by recombination with fresh mesenchyme, results in loss of adenomeres and a delay i epithelial morphogenesis. Removal of mesenchyme, but not surfact-associated MPS, yields epithelia which maintain a characteristic contour and undergo continued morphogenesis when recombined with fresh mesenchyme. Removal of MPS from these epithelia causes a loss of contour and a delay in morphogenesis. The data indicate that epithelial surface-associated MPS (or MPs-protein complexes) are required for normal epithelial morphogenesis, and that this system may serve as a model for studies of morphogenetically active materials.