Rat epidermal keratinocytes as an organotypic model for examining the role of Cx43 and Cx26 in skin differentiation

In order to characterize connexin expression and regulation in the epidermis, we have characterized a rat epidermal keratinocyte (REK) cell line that is phenotypically similar to basal keratinocytes in that they have the ability to differentiate into organotypic epidermis consisting of a basal cell layer, 2-3 suprabasal cell layers, and a cornified layer. RT-PCR revealed that REK cells express mRNA for Cx26, Cx31, Cx31.1, Cx37, and Cx43, which mimics the reported connexin profile for rat tissue. In addition, we report the expression of Cx30, Cx30.3, Cx40, and Cx45 in rat keratinocytes, highlighting the complexity of the connexin complement in rat epidermis. Furthermore, 3-dimensional analysis of organotypic skin revealed that Cx26 and Cx43 are exquisitely regulated during the differentiation process. The life-cycle of these connexins including their expression, transport, assembly into gap junctions, internalization, and degradation are elegantly depicted in organotypic epidermis as keratinocytes proceed from differentiation to programmed cell death.