Commitment of embryonic stem cells to an epidermal cell fate and differentiation in vitro

The epidermis develops from a stem cell population in the surface ectoderm that feeds a single vertical terminal differentiation pathway. To date, however, the limited capacity for the isolation or purification of epidermal stem or precursor cells has hampered studies on early commitment and differentiation events. We have developed a two-step culture scheme in which pluripotent mouse embryonic stem (ES) cells are induced first to a surface ectoderm phenotype and then are positively selected for putative epidermal stem cells. We show that the earliest stages of epidermal development follow an ordered sequence that is similar to that observed in vivo (expression of keratin 8, keratin 19, keratin 17, and keratin 14), suggesting that ES cell-derived surface ectoderm-like cells can be induced to follow the epidermal developmental pathway. At a low frequency, keratin 14-positive early epidermal cells progressed to keratin 1-positive and terminally differentiated cells producing a cornified envelope. This culturing protocol provides an invaluable system in which to study both the mechanisms that direct stem cells along the epidermal pathway as well as those that influence their subsequent epidermal differentiation.