title: Existence of Corneal Endothelial Slow-Cycling Cells.
abstract: OBJECTIVE
  To demonstrate the presence and location of corneal endothelial progenitor cells.
  
  
  METHODS
  Progenitor cell markers nestin, leucine-rich repeat-containing G-protein-coupled receptor 5, Sox9, and nerve growth factor receptor p75, as well as proliferation marker Ki-67, were examined on postnatal day (P)3, P30, and P90 corneas using immunofluorescence microscopy. Mice (P3) were pulsed with 5-bromo-2'-deoxyuridine (BrdU) and chased.
  
  
  RESULTS
  Cell proliferation was observed in all layers of P3 corneas. No posterior stromal cell proliferation was noted in P30 corneas. Progenitor cell markers were expressed in the P3 cornea, but were downregulated during maturation with minimal or no expression in P90 central corneas. In contrast, cells expressing progenitor markers were located exclusively at the corneal periphery at P90. Clusters of cells reactive for progenitor markers were in the endothelial and subendothelial space in the P90 peripheral cornea. Reactivity against BrdU was localized to the central and peripheral cornea at 1 week, and to the extreme periphery 3 weeks following a BrdU pulse. Cells reactive for both BrdU and progenitor markers were localized to the peripheral endothelium. At 3 weeks, cells reactive for BrdU and the progenitor markers were localized in the peripheral endothelium. Approximately, 20% to 45% of the progenitor marker positive cells also were labeled with BrdU.
  
  
  CONCLUSIONS
  During development, the murine corneal endothelium is composed of proliferating cells expressing progenitor markers. In contrast, in the mature endothelium slow-cycling cells, cells expressing progenitor markers and a subpopulation of slow-cycling cells expressing progenitor makers are restricted to the endothelial periphery.
authors.affiliation: Department of Molecular Pharmacology & Physiology Morsani College of Medicine, University of South Florida, Tampa, Florida, United States 2Department of Ophthalmology, Morsani College of Medicine, University of South Florida, Tampa, Florida, United States.
authors.forename: Edgar M
authors.initials: EM
authors.lastname: Espana
authors.affiliation: Department of Molecular Pharmacology & Physiology Morsani College of Medicine, University of South Florida, Tampa, Florida, United States.
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
authors.affiliation: Department of Molecular Pharmacology & Physiology Morsani College of Medicine, University of South Florida, Tampa, Florida, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Birk
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D042783:Endothelial Cells / Q000166:cytology*; D004728:Endothelium, Corneal / Q000166:cytology*; D051379:Mice; D008810:Mice, Inbred C57BL; D013234:Stem Cells / Q000166:cytology*; D013997:Time Factors