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Ultrastructural localization of gap junction protein connexin 43 in normal human skin, basal cell carcinoma, and squamous cell carcinoma

The expression and localization of connexin 43 (Cx43) were investigated in normal human epidermis, pilosebaceous apparatus, basal cell carcinoma, and squamous cell carcinoma by immunofluorescence as well as by immunoelectron microscopy. In the normal epidermis the immunofluorescence was weak in the basal layer, increased in spinous layer and negative in the horny layer. In the sebaceous gland, peripheral lobular cells showed weak cell membrane dotted pattern. Cell membrane and cytoplasmic fluorescence was strong in the central lobular cells. In the lower hair follicle, the cortex, inner and outer root sheath cells showed cell membrane fluorecence. As cortical cells underwent keratinization, they lost Cx43 epitopes. Basal cell carcinoma and squamous cell carcinoma were poorly stained, and eccrine and apocrine glands were unstained. In immunoelectron microscopy, close membrane appositions of typical gap junctions were often observed in the spinous layers of the epidermis and the immunolabeling for Cx43 was seen along the gap junction structures. Circular and long gap junctions often were found in follicular root sheaths and sebaceous glands. Gold particles labeling Cx43 in these gap junctions were found on the gap junctions or localized in the cytoplasm near the gap junction membranes. Basal cell carcinoma and squamous cell carcinoma had a small number of small gap junctions, and gold particles were not only localized to gap junctions but scattered in the cytoplasm. No gap junctions were labeled in eccrine and apocrine glands. These findings confirmed that 1) long, curved or circular membrane appositions found in hair follicle and sebaceous gland are true gap junctions, 2) immature cells such as epidermal basal cells, peripheral germinative cells of sebaceous gland and basal and squamous cell carcinoma cells do not have fully developed gap junctions, and 3) Cx43 or its precursors are present in the cytoplasm as well as on poorly developed gap junctions in these immature cells. Immunofluorescence findings generally corresponded to ultrastructural distribution and structural maturity of gap junctions.