TOPOGRAPHY OF MAMMALIAN CONNEXINS IN HUMAN SKIN

We have explored the expression of gap junction proteins in normal hum an skin by immunostaining cryostat sections (indirect immunofluorescen ce) or lyophilized epidermis (Western blotting) with antibodies agains t four mammalian connexins Cx26, Cx32, Cx40, Cx43; and by hybridizing total epidermal RNA (Northern blotting) with cRNA probes for Cx26, Cx3 2, and Cx43. We found that epidermal keratinocytes express Cx43 but no t Cx26, Cx32, or Cx40. This expression was minimal in the basal layer, much higher in the spinous layer, reduced in the granular layer, and absent in the stratum corneum. Immunostaining for Cx43 was also observ ed in sebaceous glands, hairs, and eccrine sweat ducts. The two latter epidermal adnexae were also markedly labeled by antibodies against Cx 26, a gap junction protein that was undetectable by immunofluorescence in interfollicular keratinocytes. Immunoblots of polyacrylamide gel e lectrophoresis-separated epidermal proteins and hybridization of epide rmal RNA confirmed the presence of Cx43 in epidermis. These observatio ns indicate that 1) Cx43 and Cx26 are components of human keratinocyte gap junctions; 2) these two proteins are differentially expressed in the interfollicular epidermis and the skin adnexae; 3) in interfollicu lar epidermis, Cx43 is a predominant gap junction protein, mostly expr essed by the differentiating spinous cells; 4) Cx43 distribution is in accordance with the extensive dye coupling previously observed in thi s epidermal compartment.