title: Mouse epidermal stem cells proceed through the cell cycle.
abstract: The epidermis is a continuously renewing tissue maintained by undifferentiated stem cells. For decades it has been assumed that epidermal stem cells (ESCs) were held in the G0 phase of the cell cycle and that they only entered the cell cycle when needed. Previously, we showed that ESCs retained nuclear label for long periods, indicating that these cells did not proceed through the cell cycle at the same rate as the other proliferative basal cells. However, their exact cell-cycle profile has not been determined because a pure population of ESCs has not been available. In this study, we sorted stem and transient amplifying (TA) cells from murine neonatal back skin, and adult ear, footpad, and back skin, using our recently developed method. We found that neonatal back skin had two times the number of ESCs as the adult tissues. Despite the age and anatomical difference, these ESC populations exhibited similar cell cycle profiles with approximately 96% in G0/G1 and 4% in S-G2/M. The cell cycle profiles of the TA cells from neonatal back skin and adult footpad also showed a profile similar to each other (85% in G1 and 15% in S-G2/M). Examination of genes on a cell cycle chip showed that proliferation associated genes and only p57 were upregulated in the TA cell and ESC population, respectively. We found BrdU positive and cyclin B1 positive cells in all groups, confirming that both ESCs and TA cells were cycling. These data demonstrate that there are more TA cells dividing than ESCs, that the cell cycle profile of adult TA cells is related to the proliferative state of the tissue in which they reside, and that ESC proceed through the cell cycle.
authors.affiliation: Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, Iowa, USA. martine-dunnwald@uiowa.edu
authors.forename: Martine
authors.initials: M
authors.lastname: Dunnwald
authors.forename: Sathivel
authors.initials: S
authors.lastname: Chinnathambi
authors.forename: Dana
authors.initials: D
authors.lastname: Alexandrunas
authors.forename: Jackie R
authors.initials: JR
authors.lastname: Bickenbach
mesh_terms: D000375:Aging / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D001973:Bromodeoxyuridine; D002453:Cell Cycle / Q000235:genetics*; D002454:Cell Differentiation / Q000235:genetics*; D019926:Cyclin B / Q000235:genetics; D056744:Cyclin B1; D050761:Cyclin-Dependent Kinase Inhibitor p57; D000078404:Epidermal Cells; D004817:Epidermis / Q000254:growth & development* / Q000378:metabolism; D005434:Flow Cytometry; D016193:G1 Phase / Q000235:genetics; D016195:G2 Phase / Q000235:genetics; D051379:Mice; D008813:Mice, Inbred ICR; D008938:Mitosis / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D016192:Resting Phase, Cell Cycle / Q000235:genetics; D016196:S Phase / Q000235:genetics; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism*
chemical_list: C534700:Ccnb1 protein, mouse; C493965:Cdkn1c protein, mouse; D019926:Cyclin B; D056744:Cyclin B1; D050761:Cyclin-Dependent Kinase Inhibitor p57; D009687:Nuclear Proteins; D001973:Bromodeoxyuridine