The study identifies p63 as a specific marker for keratinocyte stem cells in human corneal and epidermal tissues. P63, a transcription factor and homologue of p53, is expressed in the basal layer of the limbal epithelium and epidermal sheets but not in the transitional amplifying (TA) cells covering the corneal surface or in the suprabasal cells of the epidermis. Clonal analysis shows that p63 is abundant in holoclones (stem cells) and undetectable in paracloes (TA cells). TA cells, immediately after their withdrawal from the stem cell compartment (meroclones), have reduced p63 expression despite their high proliferative capacity. The sigma isoform of the 14-3-3 family of proteins promotes clonal evolution from stem cells to TA cells, while down-regulation of 14-3-3σ in keratinocytes prevents this process and maintains them in the stem cell compartment. The identification of p63 as a stem cell marker has significant implications for clinical applications of epithelial cultures in cell therapy and studies on epithelial tumorigenesis.The study identifies p63 as a specific marker for keratinocyte stem cells in human corneal and epidermal tissues. P63, a transcription factor and homologue of p53, is expressed in the basal layer of the limbal epithelium and epidermal sheets but not in the transitional amplifying (TA) cells covering the corneal surface or in the suprabasal cells of the epidermis. Clonal analysis shows that p63 is abundant in holoclones (stem cells) and undetectable in paracloes (TA cells). TA cells, immediately after their withdrawal from the stem cell compartment (meroclones), have reduced p63 expression despite their high proliferative capacity. The sigma isoform of the 14-3-3 family of proteins promotes clonal evolution from stem cells to TA cells, while down-regulation of 14-3-3σ in keratinocytes prevents this process and maintains them in the stem cell compartment. The identification of p63 as a stem cell marker has significant implications for clinical applications of epithelial cultures in cell therapy and studies on epithelial tumorigenesis.