Sic Transit Gloria: Farewell to the Epidermal Transit Amplifying Cell?

For the past 30 years, the prevailing model of epidermal homeostasis has been that epidermal stem cells give rise to transit amplifying cells, which undergo a limited number of cell divisions before initiating terminal differentiation. Recent studies challenge the existence of a transit amplifying cell compartment and suggest a new paradigm for epidermal homeostasis.