Tumor protein p63, typically referred to as p63, also known as transformation-related protein 63 is a protein that in humans is encoded by the TP63 (also known as the p63) gene. The TP63 gene was discovered 20 years after the discovery of the p53 tumor suppressor gene and along with p73 constitutes the p53 gene family based on their structural similarity. Despite being discovered significantly later than p53, phylogenetic analysis of p53, p63 and p73, suggest that p63 was the original member of the family from which p53 and p73 evolved. Function Tumor protein p63 is a member of the p53 family of transcription factors. p63 -/- mice have several developmental defects which include the lack of limbs and other tissues, such as teeth and mammary glands, which develop as a result of interactions between mesenchyme and epithelium. TP63 encodes for two main isoforms by alternative promoters (TAp63 and ΔNp63). ΔNp63 is involved in multiple functions during skin development and in adult stem/progenitor cell regulation. In contrast, TAp63 has been mostly restricted to its apoptotic function and more recently as the guardian of oocyte integrity. Recently, two new functions have been attributed to TAp63 in heart development and premature aging. In mice, p63 is required for normal skin development via direct transcription of the membrane protein PERP. TP63 can also regulate PERP expression with TP53 in human cancer. Clinical significance At least 42 disease-causing mutations in this gene have been discovered. TP63 mutations underlie several malformation syndromes that include cleft lip and/or palate as a hallmark feature. Mutations in the TP63 gene are associated with ectrodactyly-ectodermal dysplasia-cleft syndrome in which a midline cleft lip is a common feature, cleft lip/palate syndrome 3 (EEC3); ectrodactyly (also known as split-hand/foot malformation 4 (SHFM4)); ankyloblepharon-ectodermal dysplasia-cleft lip/palate (AEC) or Hay–Wells syndrome in which a midline cleft lip is also a common feature, Acro–dermato–ungual–lacrimal–tooth syndrome (ADULT); limb-mammary syndrome; Rap-Hodgkin syndrome (RHS); and orofacial cleft 8. Both cleft lip with or without a cleft palate and cleft palate only features have been seen to segregate within the same family with a TP63 mutation. Recently, induced pluripotent stem cells have been produced from patients affected by EEC syndromes by cell reprogramming. The defective epithelial commitment could be partially rescued by a small therapeutic compound. Molecular mechanism Transcription factor p63 is a key regulator of epidermal keratinocyte proliferation and differentiation. In a recent study, researchers used EEC-patient-derived