The epidermis and its appendages develop from a single layer of multipotent embryonic progenitor keratinocytes. Embryonic stem cells receive cues from their environment that instruct them to commit to a particular differentiation programme and generate a stratified epidermis, hair follicles or sebaceous glands. Exciting recent developments have focused on how adult skin epithelia maintain populations of stem cells for use in the natural cycles of hair follicle regeneration and for re-epithelialization in response to wounding.
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I am grateful to my many colleagues who helped to establish the groundwork for this review. I also thank J.-F. Nicolas (Pasteur Institute), H. A. Pasolli, H. Rhee and T. Lechler for their helpful suggestions about figures for this review. I am especially indebted to my former mentor, H. Green, his former postdoctoral researchers — T.-T. Sun, J. Rheinwald, F. Watt and Y. Barrandon — and to the members of my laboratory, past and present, all of whom have contributed so heavily to the field of skin biology and who have served as an enormous source of inspiration to my own contributions. E.F. is an Investigator of the Howard Hughes Medical Institute. This work was supported in part by the National Institutes of Health and the Stem Cell Research Foundation.
The author declares no competing financial interests.
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