Genomic Maintenance & Repair

Monday, October 17, 2005 3:00 PM-5:00 PM Exhibit Hall

(PP305) WRN-deficient cells exhibit unusually high rates of telomeric recombination.

Hagelstrom, R.*,1, Chang, Sandy2, Bailey, Susan1, 1 Environmental and Radiological Health Sciences, Fort Collins, Colorado, United States2 Department of Molecular Genetics, Houston, Texas, United States

ABSTRACT- Werner syndrome is a rare autosomal recessive genetic disorder characterized by premature aging, elevated genomic instability, and increased cancer incidence. The WRN gene encodes a RecQ DNA helicase involved in DNA recombination, replication and repair. We have been investigating telomere dysfunction in a mouse model that is null for both Wrn and Terc (the telomerase RNA component) that elicits a classical Werner phenotype. Cells lacking active telomerase are occasionally able to escape senescence due to telomere shortening through an alternative (i.e., telomerase-independent; ALT) pathway that is thought to maintain telomere length via some form of inter- or intrachromosomal recombination. The most common form of intrachromosomal recombination in somatic mammalian cells is sister chromatid exchange (SCE). Due to the fact that standard cytogentetic methods lack the resolution to detect SCEs that occur within a few megabases of chromosomal termini, we utilized the strand-specific hybridization technique of CO-FISH (Chromosome Orientation Fluorescence In Situ Hybridization) in order to extend SCE analysis into telomeric DNA. Our results to date reveal that telomere sister chromatid exchange (T-SCE) occurs at unusually high rates compared to the genome as a whole, and that this rate is dependent on genotype. Here, we report that late generation double knockout mouse cells (Wrn/Terc) exhibited heterogeneous telomere lengths (characteristic of ALT) and hyper recombination within the telomere proper in comparison to a WRN+/- control. Interestingly, throughout the remainder of the genome, including another block of highly repetitive sequence (pericentromeric mouse major satellite DNA) SCEs did not occur at elevated levels. We are currently utilizing RNA interference (RNAi) to knockdown the expression of WRN (and BLM, another RecQ helicase) in telomerase negative normal human fibroblasts. Our results suggest the WRN protein normally functions to repress inappropriate recombination specifically within telomeric DNA.

Key words: Werner, Telomeres

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2005 RRS