Dendritic morphology of α_E(CD103)β₇-expressing cells contacting natural murine epidermis in 2 complementary settings. (A) Epidermal sheets were separated from the dermis and prepared as outlined in “Isolation of epidermal sheets and immunohistochemistry.” K562 cells transfected with YFP alone (left panel) or YFP-fused integrin α_E-constructs and wild-type β₇ (α_E-open/YFP and β₇ shown here in middle and right panels) were seeded on the exposed undersurface of the epidermis and the formation of dendrites was visualized by confocal microscopy. Examples of filopodia extending across or between epidermal keratinocytes are indicated by arrows. The middle and the right panels show 2 different cells at a higher (middle) or lower level (right). The inserts depict the respective phase contrast images. (B) K562 cells transfected with integrin α_E-open/YFP and β₇ were seeded onto cryostat-cut sections of murine skin. The top row shows a situation where the epidermis is separated from the dermis and 2 transfectant cells are located in the resulting cleft, one cell with contact to the epidermis and one cell without. Arrows point to examples of dendrites directed toward the epidermis. The asterisk in the top left panel identifies a transfectant cell that has no contact to the epidermis and shows no formation of filopodia. In the bottom row, a transfectant cell is located across the dermo-epidermal junction. Arrows identify some dendrites extending across the epidermis. The dashed lines indicate the borders of the epidermis (including stratum corneum in the 2 bottom panels), and the diamond indicates the location of the viable epidermal cell layers. Scale bar = 10 μm. These images correspond to Videos S3 to S6.