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  • The EMBO Journal (2006) 25, 5527 - 5538
  • doi:10.1038/sj.emboj.7601411

Published online: 2 November 2006

Conditional deletion of Nbs1 in murine cells reveals its role in branching repair pathways of DNA double-strand breaks

Yun-Gui Yang1,a, Amal Saidi2, Pierre-Olivier Frappart1,b, Wookee Min2, Christelle Barrucand1, Valérie Dumon-Jones1, Jocelyne Michelon1, Zdenko Herceg1 and Zhao-Qi Wang1,2

  1. International Agency for Research on Cancer, Lyon, France
  2. Leibniz Institute for Age Research - Fritz Lipmann Institute, Jena, Germany

Correspondence to:

Zhao-Qi Wang, Leibniz Institute for Age Research – Fritz Lipmann Institute, Beutenbergstrasse 11, 07745 Jena, Germany. Tel.: +49 3641 656415; Fax: +49 3641 656413; E-mail: zqwang@fli-leibniz.de

aPresent address: Clare Hall Laboratories, Cancer Research UK, Hertfordshire EN6 3LD, UK

bPresent address: St Jude Children's Research Hospital, Memphis, TN 38105, USA

Received 27 August 2006; Accepted 6 October 2006

NBS1 forms a complex with MRE11 and RAD50 (MRN) that is proposed to act on the upstream of two repair pathways of DNA double-strand break (DSB), homologous repair (HR) and non-homologous end joining (NHEJ). However, the function of Nbs1 in these processes has not fully been elucidated in mammals due to the lethal phenotype of cells and mice lacking Nbs1. Here, we have constructed mouse Nbs1-null embryonic fibroblasts and embryonic stem cells, through the Cre-loxP and sequential gene targeting techniques. We show that cells lacking Nbs1 display reduced HR of the single DSB in chromosomally integrated substrate, affecting both homology-directed repair (HDR) and single-stranded annealing pathways, and, surprisingly, increased NHEJ-mediated sequence deletion. Moreover, focus formation at DSBs and chromatin recruitment of the Nbs1 partners Rad50 and Mre11 as well as Rad51 and Brca1 are attenuated in these cells, whereas the NHEJ molecule Ku70 binding to chromatin is not affected. These data provide a novel insight into the function of MRN in the branching of DSB repair pathways.

  • Keywords:

    • DNA double-strand break,
    • homology-directed repair,
    • NBS1,
    • nonhomologous end-joining,
    • single-stranded annealing