DNA methylation and differentiation of human keratinocytes.

DNA methylation is a postreplicative modification thought to play a role in gene transcription in eucaryotes. Differences in the amount of 5-methylcytosine as a function of age and differentiation state have been reported. DNA isolated from human skin keratinocytes was analyzed for its 5-methylcytosine content. The 5-methylcytosine in DNA from neonatal and adult human keratinocytes was found to vary as a function of differentiation state. Differentiation of keratinocytes in vitro was promoted using a simple method where keratinocytes were plated directly onto the plastic surface of a culture flask, grown to confluence, and placed on a rocking culture platform that cyclically exposed the cells to air 50% of the time. Terminal differentiation was evident after approximately three weeks in culture. The 5-methylcytosine content of the DNA from differentiated human keratinocytes was 1.4%, whereas that of undifferentiated human keratinocytes was 3.1%. No difference in the 5-methylcytosine content of DNA as a function of the age of the donor was found.