title: Crypt base columnar stem cells in small intestines of mice are radioresistant.
abstract: OBJECTIVE
  Adult stem cells have been proposed to be quiescent and radiation resistant, repairing DNA double-strand breaks by nonhomologous end joining. However, the population of putative small intestinal stem cells (ISCs) at position +4 from the crypt base contradicts this model, in that they are highly radiosensitive. Cycling crypt base columnar cells (CBCs) at crypt positions +1-3 recently were defined as an alternative population of ISCs. Little is known about the sensitivity of this stem cell population to radiation.
  
  
  METHODS
  Radiation-induced lethality of CBCs was quantified kinetically in Lgr5-lacZ transgenic mice. γ-H2AX, BRCA1, RAD51, and DNA-PKcs foci were used as DNA repair surrogates to investigate the inherent ability of CBCs to recognize and repair double-strand breaks. 5-ethynyl-2'-deoxyuridine and 5-bromo-2'-deoxyuridine incorporation assays were used to study patterns of CBC growth arrest and re-initiation of cell cycling. Apoptosis was evaluated by caspase-3 staining.
  
  
  RESULTS
  CBCs are relatively radioresistant, repairing DNA by homologous recombination significantly more efficiently than transit amplifying progenitors or villus cells. CBCs undergo apoptosis less than 24 hours after irradiation (32% ± 2% of total lethality) or mitotic death at 24-48 hours. Survival of CBCs at 2 days predicts crypt regeneration at 3.5 days and lethality from gastrointestinal syndrome. Crypt repopulation originates from CBCs that survive irradiation.
  
  
  CONCLUSIONS
  Adult ISCs in mice can cycle rapidly yet still be radioresistant. Importantly, homologous recombination can protect adult stem cell populations from genotoxic stress. These findings broaden and refine concepts of the phenotype of adult stem cells.
authors: Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York.
authors: Guoqiang
authors: G
authors: Hua
authors: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
authors: Tin Htwe
authors: TH
authors: Thin
authors: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
authors: Regina
authors: R
authors: Feldman
authors: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
authors: Adriana
authors: A
authors: Haimovitz-Friedman
authors: Hubrecht Institute, KNAW and University Medical Center Utrecht, Uppsalalaan 8, 3584CT Utrecht, The Netherlands.
authors: Hans
authors: H
authors: Clevers
authors: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York.
authors: Zvi
authors: Z
authors: Fuks
authors: Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York. Electronic address: r-kolesnick@ski.mskcc.org.
authors: Richard
authors: R
authors: Kolesnick
mesh_terms: D053687:Adult Stem Cells / Q000528:radiation effects*; D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D001853:Bone Marrow / Q000528:radiation effects; D059447:Cell Cycle Checkpoints / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair; D007583:Jejunum / Q000473:pathology / Q000528:radiation effects*; D051379:Mice; D008822:Mice, Transgenic; D011836:Radiation Tolerance