International Mammalian Genome Society

logo18th International Mouse Genome Conference

17-22 October 2004, Seattle, USA


ORAL PRESENTATION

WEDNESDAY OCTOBER 20

8.30pm – 8.45pm

MAINTAINING TELOMERE AND CHROMOSOME STABILITY REQUIRE THE RAD51D HOMOLOGOUS RECOMBINATION GENE

Smiraldo PG1, Tarsounas M3, Gruver AM1, Osborn JC1, Munoz P2, Class A3, Blasco MA2, West SC3, Pittman DL1

1 Medical College of Ohio, Toledo, United States, 2 Spanish National Cancer Center, Madrid, Spain, 3 Cancer Research UK, London Research Institute, Hertfordshire, United Kingdom

Homologous recombination (HR) is a double-strand break repair pathway required for resistance to DNA damage and maintaining genomic integrity. In mitotically dividing cells, the primary proteins involved in HR repair are RAD51 and the five RAD51 paralogs, RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3. By investigating Rad51d knockout mice and mammalian cell lines, we demonstrate that RAD51D is critical for maintaining chromosome stability and telomere protection. Homozygous mice defective for Rad51d die prior to birth, and cells derived from mutant embryos fail to proliferate in culture, likely as a result of genomic instability and p53 activation. A p53 deletion is sufficient to extend the lifespan of Rad51d-deficient embryos by up to 6 days and rescue the cell lethal phenotype. Rad51d-/- Trp53-/- mouse embryo derived fibroblasts were sensitive to DNA-damaging agents, particularly interstrand crosslinks, and exhibited extensive chromosome instability including aneuploidy, chromosome fragments, deletions, and complex rearrangements. Additionally, loss of Rad51d resulted in increased centrosome fragmentation and reduced levels of radiation-induced RAD51-focus formation. Spontaneous frequencies of sister chromatid exchange (SCE) were not affected by the absence of Rad51d, but SCE frequencies did fail to be induced upon challenge with the DNA cross-linking agent mitomycin C. The RAD51D protein was recently found to localize at telomeres.  Decreased telomere lengths and increased levels of anaphase bridging and telomere fusions were observed in primary Rad51d-deficient cells. Similarly, inhibition of RAD51D synthesis by RNA interference in human cells resulted in increased telomere fusions.  These findings support a crucial role for RAD51D in maintaining the integrity of the mammalian genome.

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