The epidermis of the skin is a stratified squamous epithelium, which plays an important protective role. It manifests this role by building an extensive cytoskeletal architecture, the unique feature of which is the presence of keratin filaments. There are two major pairs of keratins in the epidermis: one pair is expressed in dividing cells and the other expressed in terminally differentiating cells. As such, keratins provide useful biochemical markers to explore the molecular mechanisms underlying the balance between growth and differentiation in the epidermis. Here, I review what is currently known about epidermal growth and differentiation, and how an understanding of keratin gene expression has been useful in elucidating regulatory pathways in the skin.

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