Farewell to the transit amplifying cell comparment

28 March 2008

Ben Simons
Cavendish Laboratory of Physics
University of Cambridge


It is widely assumed that, in adults, progenitor cells can be classified into one of two cell types according to their proliferative potential: long-lived, slowly-cycling stem cells, capable of long-term self-renewal, can differentiate to form short-lived transit amplifying cells, which in turn undergo several rounds of division before terminal differentiation. In many tissues, the maintenance and survival of stem cells is regulated by inputs from the local microenvironment or niche. However, recent studies have found that, in murine interfollicular epidermis, normal tissue is maintained by a single progenitor cell population, committed to terminal differentiation. Although, as a population, their ability to self-renew suggests that these cells belong to a stem cell compartment, their individual characteristics are more reminiscent of a transit compartment, but with an exit probability that has no memory of past division. Drawing on recent experimental and theoretical results, we discuss the design advantages of stochastic progenitor cell fate, the mouting evidence that other adult tissues conform to the same dynamics, and the implications for carcinogenesis.


  1. E Clayton, D P Doupe, A M Klein, D J Winton, B D Simons, P H Jones, "A single type of progenitor cell maintains normal epidermis", Nature 446:185-9 2007. PubMed
  2. P Jones, B D Simons, "Epidermal homeostasis: do committed progenitors work while stem cells sleep?", Nat Rev Mol Cell Biol 9:82-8 2008. PubMed

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