The effect of detachment of cultured epithelial sheets on cellular ultrastructure and organisation

In this morphological study the (ultra)structural changes that lead to contraction of detached cultured epithelium were investigated. Keratinocytes, isolated from human skin and oral mucosa, were grown to form stratified cell sheets. The multilayers were examined with light and electron microscopy before, during and after detachment from the culture vessel. Attached epithelium had a stretched morphology with flattened cells and nuclei. Evidence is provided that after enzymatical detachment with dispase (1) basal cells became columnar by contraction of actin bundles in the basal cortex, which was accompanied by blebbing of the basal cell membrane; (2) in all cell layers cytokeratin bundles contracted resulting in displacement of desmosomes and a spherical shape of the cells and nuclei. By slow dispase-detachment at 4 degrees C or by quick mechanical detachment, shrinkage of the sheet was partly suppressed but contraction of cytokeratin and related events occurred indicating that these were the result of the spontaneous reassembly of the intermediate filament system. The results suggested that the shape and ultrastructure of all cells in an epithelial multilayer are dependent on the interaction of the basal cells with the underlying extracellular matrix.