Retinoic Acid Regulates, in vitro, the Two Normal Pathways of Differentiation of Human Laryngeal Keratinocytes

We have investigated the regulation of the two normal differentiation pathways followed by laryngeal epithelium. Using a tissue culture system that permits growth of cells at the air-liquid interface in serum-free medium, we found that modulating the concentration of retinoic acid is sufficient to determine which pathway is used. At$10^{-8} M$retinoic acid, the cells form a stratified squamous epithelium which expresses the differentiation-specific keratin K13. At 10-7M retinoic acid, the cells form a ciliated pseudostratified epithelium, with no expression of K13. These results are distinct from those seen with foreskin keratinocytes, which have only a single pathway of normal differentiation.