Expression profiles of cell-cell and cell-matrix junction proteins in developing human epidermis.

The spatial distribution of a panel of cell junction proteins was studied in developing human epidermis by confocal laser scanning microscopy. The results demonstrated that many of the cell junction proteins were expressed in early two-layered embryonic epidermis, but their subcellular distribution displayed marked changes during development. Specifically, desmosomal proteins, desmoplakin, desmocollin and desmoglein, adherens junction components, E-cadherin, alpha-catenin and vinculin, and an actin-binding protein alpha-actinin were expressed as early as 8 weeks of estimated gestational age (EGA). Type IV collagen and beta1 and beta4 integrins were also present. At this early developmental stage, the epidermis is known to comprise two layers of cells, the basal layer and the peridermal layer. In addition to being present in cell-cell contacts, desmosomal antigens and E-cadherin were unexpectedly localized to the basal aspect of basal cells in samples at 8 weeks. On the other hand, talin, which in adult skin is localized to the dermal-epidermal junction, could not be detected until 12 weeks. These results suggest that the separation of cell membranes to the basal and apicolateral compartments does not occur before the maturation of the basement membrane zone. At 8 weeks EGA, gap junction antigen connexin 43 was expressed in scarce spots in cell-cell contacts of basal cells. In samples of 11-21 weeks EGA, the density of desmosomal and adherens junction markers as well as connexin 43 increased in cell-cell junctions, together with the appearance of the intermediate cell layer and beginning of stratification of the epidermis.