Office of Biological and Environmental Research

DOE Lowdose Radiation Program Workshop V

2005 Abstract

Title: ‘Recombomice’ – A new tool for studying homologous recombination in vivo

Authors: Carrie Hendricks ¹, Olga Kovalchuk ², and Bevin Engelward ¹

Institutions: ¹Division of Biological Engineering, MIT, Cambridge, MA
²Department of Biological Sciences, University of Lethbridge, Alberta, Canada

Homology directed repair is critical for genomic stability. However, misalignments and exchanges can lead to deleterious deletions, insertions and loss of heterozygosity (LOH) events that contribute to cancer. We have recently developed ‘Recombomice’ in which recombinant cells fluoresce, allowing direct in vivo detection of recombinant cells in somatic tissue for the first time. The Fluorescent Yellow Direct Repeat (FYDR) mice carry an engineered direct repeat recombination substrate that yields expression of enhanced yellow fluorescent protein (EYFP) following homologous recombination. The FYDR mice provide a remarkably sensitive assay for environmental, genetic, and epigenetic factors that affect recombination. In addition, fluorescence microscopy and histology can be used to detect recombinant cells within intact pancreatic tissues, thus raising the possibility of studying the relative susceptibility of various cell types to genetic and environmental factors that modulate homologous recombination. In recent studies of ionizing radiation induced recombination, we have shown that chronic irradiation suppresses the frequency of homologous recombination events to levels below those of unexposed animals. These results are consistent with previous studies showing that ionizing radiation induces an adaptive response. We have initiated studies of the underlying molecular basis for this effect, and found that the levels of several key DNA repair proteins known to facilitate clearance of recombinogenic DNA lesions are upregulated in the chronically irradiated animals (namely, Polymerase b [Polb] and Ku70, which is required for nonhomologous endjoining [NHEJ]). Current research is aimed at delineating the dose range at which these effects occur, and revealing the molecular basis for radiosuppression of homologous recombination in vivo.