cellular phenotype

• abnormal cell physiology
  • mouse embryonic cells are more sensitive to DNA damage induced by radiation compared to wild type cells
  (MGI Ref ID J:194603)

• abnormal DNA repair
  • mouse embryonic fibroblasts exhibit suppression of chromosome end fusion events at telomeres induced by expression of a dominant negative Terf2
  (MGI Ref ID J:195061)

• abnormal double-strand DNA break repair
  • increased single-strand DNA formation due to increased DNA end resection in MEFs
  (MGI Ref ID J:231089)

• increased cellular sensitivity to hydroxyurea
  (MGI Ref ID J:194603)

• increased cellular sensitivity to ionizing radiation
  (MGI Ref ID J:194603)
  • increased Rpa2 phosphorylation after treatment with radiomimetic drug neocarzinostatin (NCS) in MEFs
  (MGI Ref ID J:231089)
  • severe reduction in number of ionizing radiation induced Rif1 foci in MEFs
  (MGI Ref ID J:231089)

homeostasis/metabolism phenotype

• abnormal DNA repair
  • mouse embryonic fibroblasts exhibit suppression of chromosome end fusion events at telomeres induced by expression of a dominant negative Terf2
  (MGI Ref ID J:195061)

• abnormal double-strand DNA break repair
  • increased single-strand DNA formation due to increased DNA end resection in MEFs
  (MGI Ref ID J:231089)

immune system phenotype

• abnormal class switch recombination
  • impaired but partially rescued by short hairpin RNA inhibition of Rbbp8 and enhanced by treatment with the WRNi helicase inhibitor or to a lesser extent the ATM inhibitor Ku55933
  (MGI Ref ID J:194603)
  • severely impaired IgM-to-IgG1 CSR in splenic B cells stimulated with interleukin-4 and lipopolysaccharide
  (MGI Ref ID J:231089)

hematopoietic system phenotype

• abnormal class switch recombination
  • impaired but partially rescued by short hairpin RNA inhibition of Rbbp8 and enhanced by treatment with the WRNi helicase inhibitor or to a lesser extent the ATM inhibitor Ku55933
  (MGI Ref ID J:194603)
  • severely impaired IgM-to-IgG1 CSR in splenic B cells stimulated with interleukin-4 and lipopolysaccharide
  (MGI Ref ID J:231089)

cellular phenotype

• abnormal cell cycle checkpoint function
  • at 24 hrs after IR, the % of mitotic cells is ~3-fold lower in nocodazole-treated mutant MEFs than in wild-type cells, as assessed by immunostaining with anti-phospho-histone H3 antibodies
  (MGI Ref ID J:82512)
  • at 30 min after exposure to 20 Gy of IR, mutant MEFs show a slight defect in intra-S-phase checkpoint regulation relative to wild-type MEFs
  (MGI Ref ID J:82512)
  • Normal - however, mutant MEFs, synchronized by a cycle of serum starvation and release, show a normal G₁ arrest in response to 10 to 20 Gy of IR
  (MGI Ref ID J:82512)
  • several hrs after exposure to 6 Gy of ionizing radiation (IR), mutant MEFs, like wild-type MEFs, are arrested in G₂ but display a delayed exit from the G₂/M phase
  (MGI Ref ID J:82512)

• aneuploidy
  • mutant MEFs (passage 3) show a tendency toward aneuploidy
  (MGI Ref ID J:82512)

• chromosomal instability
  • Normal - however, no spontaneous chromosomal breaks are detected in mutant MEFs
  (MGI Ref ID J:82512)
  • mutant MEFs (passage 3) show a tendency toward aneuploidy and/or tetraploidy, suggesting a defect in chromosome segregation
  (MGI Ref ID J:82512)

• decreased cell proliferation
  • MEFs derived from E14.5 homozygous mutant embryos display a reduced proliferation rate relative to wild-type MEFs
  (MGI Ref ID J:82512)

• increased cellular sensitivity to ionizing radiation
  • mutant ES cells show a 2- to 3-fold increase in ionizing radiation sensitivity relative to wild-type ES cells, revealed by in vitro clonogenic survival assays
  (MGI Ref ID J:82512)

endocrine/exocrine gland phenotype

• increased T cell derived lymphoma incidence
  • at 4 to 7 months of age, 8% of homozygotes develop massive thymic lymphomas with or without infiltration of the lymph nodes, spleen, and kidney, not observed in wild-type or heterozygous control mice
  (MGI Ref ID J:82512)
  • three of these tumors display a CD4⁺ CD8⁺ immunophenotype
  (MGI Ref ID J:82512)

• thymus hypoplasia
  • homozygotes show a 40% reduction in thymus cellularity relative to wild-type littermates
  (MGI Ref ID J:82512)

growth/size/body region phenotype

• decreased body size
  • homozygotes are significantly smaller than wild-type and heterozygous control mice
  (MGI Ref ID J:82512)

• decreased body weight
  • at 5 months of age, both male and female homozygotes weigh significantly less than their wild-type or heterozygous counterparts
  (MGI Ref ID J:82512)

• postnatal growth retardation
  • homozygotes of both sexes are growth retarded relative to wild-type or heterozygous control littermates
  (MGI Ref ID J:82512)

hematopoietic system phenotype

• decreased CD4-positive, alpha beta T cell number
  • at 6 weeks of age, homozygotes show a ~2-fold reduction in the percentage of CD4⁺ mature thymocytes and peripheral CD4⁺ T lymphocytes relative to wild-type littermates
  (MGI Ref ID J:82512)

• increased double-negative T cell number
  • at 6 weeks of age, homozygotes show a maximum 2-fold increase in the percentage of CD4^- CD8^- progenitors relative to wild-type littermates
  (MGI Ref ID J:82512)

• thymus hypoplasia
  • homozygotes show a 40% reduction in thymus cellularity relative to wild-type littermates
  (MGI Ref ID J:82512)

homeostasis/metabolism phenotype

• increased mortality induced by ionizing radiation
  • in response to 8 Gy of whole body ionizing radiation (IR), all homozygotes die by 14 days from radiation-induced intestinal bleeding and bone marrow failure, whereas most wild-type mice remain viable for at least 2 months after IR treatment
  (MGI Ref ID J:82512)

immune system phenotype

• decreased CD4-positive, alpha beta T cell number
  • at 6 weeks of age, homozygotes show a ~2-fold reduction in the percentage of CD4⁺ mature thymocytes and peripheral CD4⁺ T lymphocytes relative to wild-type littermates
  (MGI Ref ID J:82512)

• increased double-negative T cell number
  • at 6 weeks of age, homozygotes show a maximum 2-fold increase in the percentage of CD4^- CD8^- progenitors relative to wild-type littermates
  (MGI Ref ID J:82512)

• thymus hypoplasia
  • homozygotes show a 40% reduction in thymus cellularity relative to wild-type littermates
  (MGI Ref ID J:82512)

mammalian phenotype

• reproductive system phenotype
  • Normal - male homozygotes show no overt defects in spermatogenesis, suggesting normal meiosis
  (MGI Ref ID J:82512)

mortality/aging

• increased mortality induced by ionizing radiation
  • in response to 8 Gy of whole body ionizing radiation (IR), all homozygotes die by 14 days from radiation-induced intestinal bleeding and bone marrow failure, whereas most wild-type mice remain viable for at least 2 months after IR treatment
  (MGI Ref ID J:82512)

• premature death
  • 9% of homozygotes die at the ages of 1 to 7 months in the absence of overt detectable tumors; possibly due to opportunistic infections
  (MGI Ref ID J:82512)

neoplasm

• increased lymphoma incidence
  • homozygotes exhibit an increased incidence of malignant lymphomas, putatively due to an inability to detect or repair abnormal V(D)J recombination
  (MGI Ref ID J:82512)

• increased T cell derived lymphoma incidence
  • at 4 to 7 months of age, 8% of homozygotes develop massive thymic lymphomas with or without infiltration of the lymph nodes, spleen, and kidney, not observed in wild-type or heterozygous control mice
  (MGI Ref ID J:82512)
  • three of these tumors display a CD4⁺ CD8⁺ immunophenotype
  (MGI Ref ID J:82512)

reproductive system phenotype

• decreased litter size
  • although both male and female homozygotes are fertile, the average litter size of homozygous mutant intercrosses is slightly reduced relative to that of wild-type intercrosses
  (MGI Ref ID J:82512)