Journal Article

An inducible null mutant murine model of Nijmegen breakage syndrome proves the essential function of <i>NBS1</i> in chromosomal stability and cell viability

Ilja Demuth, Pierre-Olivier Frappart, Gabriele Hildebrand, Anna Melchers, Stephan Lobitz, Lars Stöckl, Raymonda Varon, Zdenko Herceg, Karl Sperling, Zhao-Qi Wang and Martin Digweed

in Human Molecular Genetics

Volume 13, issue 20, pages 2385-2397
Published in print October 2004 | ISSN: 0964-6906
Published online August 2004 | e-ISSN: 1460-2083 | DOI:
An inducible null mutant murine model of Nijmegen breakage syndrome proves the essential function of NBS1 in chromosomal stability and cell viability

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The human genetic disorder, Nijmegen breakage syndrome, is characterized by radiosensitivity, immunodeficiency, chromosomal instability and an increased risk for cancer of the lymphatic system. The NBS1 gene codes for a protein, nibrin, involved in the processing/repair of DNA double strand breaks and in cell cycle checkpoints. Most patients are homozygous for a founder mutation, a 5 bp deletion, which might not be a null mutation, as functionally relevant truncated nibrin proteins are observed, at least in vitro. In agreement with this hypothesis, null mutation of the homologous gene, Nbn, is lethal in mice. Here, we have used Cre recombinase/loxP technology to generate an inducible Nbn null mutation allowing the examination of DNA-repair and cell cycle-checkpoints in the complete absence of nibrin. Induction of Nbn null mutation leads to the loss of the G2/M checkpoint, increased chromosome damage, radiomimetic-sensitivity and cell death. In vivo, this particularly affects the lymphatic tissues, bone marrow, thymus and spleen, whereas liver, kidney and muscle are hardly affected. In vitro, null mutant murine fibroblasts can be rescued from cell death by transfer of human nibrin cDNA and, more significantly, by a cDNA carrying the 5 bp deletion. This demonstrates, for the first time, that the common human mutation is hypomorphic and that the expression of a truncated protein is sufficient to restore nibrin's vital cellular functions.

Journal Article.  8009 words.  Illustrated.

Subjects: Genetics and Genomics

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