Basic Mechanisms of Genome Stability
Mammalian cells employ two predominant DSB repair pathways: nonhomologous end joining (NHEJ), which repairs DNA breaks by the ligation of two broken ends without respect to sequence homology; and homologous recombination (HR), which uses homology on an undamaged template to catalyze high fidelity repair.
Nonhomologous end joining and chromosomal fragile site stability
One type of chromosomal damage thought to be involved in tumorigenesis is fragile site breakage. Recent evidence has indicated that fragile site breakage may be related to DNA replication stress, but almost nothing is known about the DNA repair pathways that respond after breakage has occurred. We are currently examining the role of NHEJ in repair of chromosomal fragile sites, using classical cytogenetic methods, fluorescence in situ hybridization (FISH), and spectral karyotyping (SKY) to monitor fragile site stability, and the consequences of fragile site breakage, in cell lines and primary cells derived from NHEJ-deficient mice.
Homologous recombination in lymphocyte development and DSBR
Because NHEJ is important for general genome stability, it is not surprising the lymphomas that develop in an NHEJ-deficient setting exhibit numerous chromosomal abnormalities. Unexpectedly, however, pre-malignant, NHEJ-deficient pro-B cells show very little genomic instability. This is an interesting paradox, which may be explained by the reliance of pro-B cells on another DSB repair pathway such as homologous recombination (HR). We are testing this hypothesis, in culture and in vivo, by taking advantage of cells deficient for the XRCC2 homologous recombination factor.
