Schematic steps of reprogramming somatic cells, such as fibroblasts, to induced pluripotent stem (iPS) cells, and their differentiation into epidermal keratinocytes capable of forming skin-like structures. The reprogramming process is initiated by introduction of transcription factors (cMYC, SOX2, OCT4 and KLF4) into the somatic cells by transduction of expression vectors, synthetic mRNA or recombinant protein. The iPS cells have characteristic features that allow their identification and enrichment. The iPS cells can then be differentiated into keratinocytes under specific culture conditions, e.g., medium supplemented with retinoic acid (RA) and bone morphogenic protein-4 (BMP-4). BMZ, basement membrane zone. (Adapted from Uitto, 2011b).