title: Exposure to gamma-rays at the telogen phase of the hair cycle inhibits hair follicle regeneration at the anagen phase in mice.
abstract: OBJECTIVE
  The effects of ionizing radiations on somatic stem cells largely remain to be studied. Hair follicles are self-renewing structures that reconstitute themselves throughout the hair cycle, which is comprised of the following phases: Anagen (growth), catagen (regression) and telogen (resting), suggesting the presence of their own stem cells.
  
  
  METHODS
  The whole bodies of C57BL/10JHir mice in the 1st telogen phase were irradiated with γ-rays. Mice were examined for effects on hair follicles, including their number, morphology and pigmentation in the 2nd anagen phase.
  
  
  RESULTS
  Decreased hair follicle density and induction of curved hair follicles were observed in the dermal skin of irradiated mice. In addition to these keratinocyte-derived anomalies, melanocyte-derived anomalies including white hair and hypopigmented hair bulbs were found. The decrease in hair follicle density and the increase in the frequency of hypopigmented hair bulbs were dependent on the dose of γ-rays.
  
  
  CONCLUSIONS
  These results suggest that γ-rays damage stem cells and progenitors for keratinocytes and melanocytes, thereby affecting the structure and character of regenerated hair follicles. The density of hair follicles and pigment production in hair bulbs are established as criteria for the effects of γ-rays on the hair cycle.
authors.affiliation: Fukushima Project Headquarters, National Institute of Radiological Sciences , Chiba , Japan.
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Sugaya
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hirobe
mesh_terms: D000818:Animals; D004249:DNA Damage; D005720:Gamma Rays; D018859:Hair Follicle / Q000502:physiology / Q000528:radiation effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D012038:Regeneration / Q000528:radiation effects*; D013234:Stem Cells / Q000166:cytology / Q000528:radiation effects