Expression of gap junction proteins connexin 26 and 43 is modulated during differentiation of keratinocytes in newborn mouse epidermis.

We examined the expression of the gap junction proteins connexin 26 (Cx26), 32 (Cx32), and 43 (Cx43) in keratinocytes of newborn mouse epidermis to elucidate which connexins are expressed in keratinocytes in intact skin of newborn mice, and whether the expression of connexins is modulated during terminal differentiation of keratinocytes. Immunofluorescent staining using antibodies against Cx26, Cx32, and Cx43 combined with type-specific anti-keratin immunohistochemistry showed that Cx26 was expressed in keratinocytes in the granular layer and in the upper part of the squamous layer, whereas Cx43 was localized in keratinocytes in the basal layer and in the lower part of the squamous layer. No specific staining of Cx32 was found in mouse epidermis. Double staining of Cx26 and Cx43 revealed that some keratinocytes in the squamous layer expressed both connexins, but that in most cases localization of the two kinds of connexins was different, i.e., Cx26 was localized on the upper surface, whereas Cx43 was present on the lower surface of the plasma membrane of keratinocytes. Northern and Western blot analyses confirmed that Cx26 and Cx43, but not Cx32, were expressed at mRNA and protein levels in newborn mouse skin. These results suggest that the modulation of connexin expression from Cx43 to Cx26 takes place during terminal differentiation of keratinocytes in mouse epidermis.