  The epidermis is a specialized epithelium that constitutes the outermost
layer of the skin, and it provides a protective barrier against environmental
assaults. Primarily consisting of multilayered keratinocytes, the epidermis is
continuously renewed by proliferation of stem cells and the differentiation of
their progeny, which undergo terminal differentiation as they leave the basal
layer and move upward toward the surface, where they die and slough off. Basal
keratinocytes rest on a basement membrane at the dermal-epidermal junction that
is composed of specific extracellular matrix proteins organized into
interactive and mechanically supportive networks. Firm attachment of basal
keratinocytes, and their dynamic regulation via focal adhesions and
hemidesmosomes, is essential for maintaining major skin processes, such as
self-renewal, barrier function, and resistance to physical and chemical
stresses. The adhesive integrin receptors expressed by epidermal cells serve
structural, signaling, and mechanosensory roles that are critical for epidermal
cell anchorage and tissue homeostasis. More specifically, the basement membrane
components play key roles in preserving the stem cell pool, and establishing
cell polarity cues enabling asymmetric cell divisions, which result in the
transition from a proliferative basal cell layer to suprabasal cells committed
to terminal differentiation. Finally, through a well-regulated sequence of
synthesis and remodeling, the components of the dermal-epidermal junction play
an essential role in regeneration of the epidermis during skin healing. Here
too, they provide biological and mechanical signals that are essential to the
restoration of barrier function.
