Effects of retinoic acid on the differentiation of hamster cheek pouch epithelium grown in vitro.

Recently our laboratories have successfully attained preferential epithelial outgrowths from hamster cheek pouch explants. This has allowed us to systematically analyze oral epithelial cell differentiation as weel las examine the modulatory effects of various physiologic and pharmacologic agents in this epithelial cell system. The objective of the current investigation was to study the effects of various doses of retinoic acid (RA) on the epithelial outgrowths of hamster cheek pouch. Light microscopic observations employing colcemid treatment indicated that 10 IU/ml RA enhanced mitotic activity of the epithelium up to 25%. Scanning electron microscopic observations of control cultures showed flat, polyhedral epithelial cells containing thin long microvilli connecting the adjacent cells. In contrast, cultures treated with 10 IU/ml RA showed round or spherical cells exhibiting short of medium sized thicker microvilli. These were covered with a fuzzy appearing layer probably representing glycocalyx. Many bleb-like formation were also observed. Transmission electron microscopic examination of the control cultures showed the presence of tonofilaments and desmosomes, characteristic components of the keratinizing epithelia. In contrast, the RA treated cultures included cells which apparently were either devoid of tonofilaments or contained few fine filaments and small intercellular functions. In addition many vacuoles as well as variable numbers of electron-dense and electron-lucent granules were observed. Thus, it appears that RA inhibited keratinization and altered the differentiation pattern of keratinization and altered the differentiation pattern of keratinizing epithelium.