Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair.
The N-end rule pathway of protein degradation targets proteins with destabilizing N-terminal residues. Ubr2 is one of the E3 ubiquitin ligases of the mouse N-end rule pathway. We have previously shown that Ubr2-/- male mice are infertile, owing to the arrest of spermatocytes between the leptotene/zygotene and pachytene of meiosis I, the failure of chromosome pairing, and subsequent apoptosis. Here, we report that mouse fibroblast cells derived from Ubr2-/- embryos display genome instability. The frequency of chromosomal bridges and micronuclei were much higher in Ubr2-/- fibroblasts than in +/+ controls. Metaphase chromosome spreads from Ubr2-/- cells revealed a high incidence of spontaneous chromosomal gaps, indicating chromosomal fragility. These fragile sites were generally replicated late in S phase. Ubr2-/- cells were hypersensitive to mitomycin C, a DNA cross-linking agent, but displayed normal sensitivity to gamma-irradiation. A reporter assay showed that Ubr2-/- cells are significantly impaired in the homologous recombination repair of a double strand break. In contrast, Ubr2-/- cells appeared normal in an assay for non-homologous end joining. Our results therefore unveil the role of the ubiquitin ligase Ubr2 in maintaining genome integrity and in homologous recombination repair.
Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
Yan
Y
Ouyang
Yong Tae
YT
Kwon
Jee Young
JY
An
Danny
D
Eller
Shih-Chang
SC
Tsai
Silvia
S
Diaz-Perez
Joshua J
JJ
Troke
Michael A
MA
Teitell
York
Y
Marahrens
D000818:Animals; D002478:Cells, Cultured; D002873:Chromosome Fragility / Q000235:genetics*; D004249:DNA Damage / Q000235:genetics; D004260:DNA Repair / Q000235:genetics*; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000502:physiology; D017930:Genes, Reporter; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D011995:Recombination, Genetic; D044767:Ubiquitin-Protein Ligases / Q000172:deficiency* / Q000235:genetics*
C511160:UBR2 protein, mouse; D044767:Ubiquitin-Protein Ligases