1. Distinct Contribution of Stem and Progenitor Cells to Epidermal Maintenance Carolina Marrero

2. The skin interfollicular epidermis(IFE) is the first barrier against external environment and its maintenance is critical for survival(Mascré). There are two theories that propose how homeostasis is maintained. There are long-lived slow-cycling stem cells that give rise to transit-amplifying cell progeny(Mascré). That it is achieved by a single committed progenitor population that balances stochastic fate(Mascré). Overview

3. The epidermis is made up of a base layer of proliferative cells and suprabasal layers of differentiated cells. These are enucleated and form squames that are shed from the cornified layer. Depending on the species and the location of the skin, the time it takes for cells to transit from the basal layer to the cornified layer is 1-2 weeks. IFE

4. IFE is organized into EPUs(epidermal proliferative units), which are made of slow- cycling stem cells which turn into transit- amplifying cells. First Theory

5. The second theory suggests that tissue is preserved by a single, equipotent, committed progenitor cell population in which the balance between proliferation and differentiation follows seemingly random cell fate decision(Mascré). Theory 2

6. In this experiment, two different Cre-ER transgenic mice are injected with tamoxifen in the basal layer of the tail. This was done to determine how epidermal cells maintain homeostasis when the epidermis is wounded and to test which theory proved correct in the healing of the wound. The Experiment

7. Stem cells contribute significantly to the restoration and regeneration of the wound(long-term). Committed progenitor cells make a limited contribution(short-term). Committed progenitor cells divide quicker than stem cells do, but the stem cells provide more of what the wound needs to heal. Conclusion

9. The epidermis is important and maintaining its homeostasis is critical. Both theories of maintaining homeostasis are correct. Stem cells take longer to divide, but are more important in the long run for the healing of the wound. Key Points

10. Overall, I thought this was an interesting article. I never knew that there were so many different types of cells that work to heal wounds. I think that there should have been a bit more background information, because that is what confused me when I was reading the method for the experiment. Personal Thoughts

11. Mascré, Guilhem, et al. "Distinct Contribution of Stem and Progenitor Cells to Epidermal Maintenance." Nature 489.7415 (2012): 257-62. Print. Bibliography