Engineering translocations with delayed replication: evidence for cis control of chromosome replication timing
Kevin S. Breger,
Leslie Smith and
Mathew J. Thayer*
Division of Molecular Medicine, Oregon Health and Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA
* To whom correspondence should be addressed. Tel: +1 5034942447; Fax: +1 5034947368; Email: email@example.com
Received June 13, 2005; Accepted August 10, 2005
An open article from Human Molecular Genetics 2005 14(19):2813-2827; doi:10.1093/hmg/ddi314.
Certain chromosome rearrangements, found in cancer cells orin cells exposed to ionizing radiation, exhibit a chromosome-widedelay in replication timing (DRT) that is associated with adelay in mitotic chromosome condensation (DMC). We have developeda chromosome engineering strategy that allows the generationof chromosomes with this DRT/DMC phenotype. We found that 10%of inter-chromosomal translocations induced by two distinctmechanisms, site-specific recombination mediated by Cre or non-homologousend joining of DNA double-strand breaks induced by I-Sce1, resultin DRT/DMC. Furthermore, on certain balanced translocationsonly one of the derivative chromosomes displays the phenotype.Finally, we show that the engineered DRT/DMC chromosomes acquiregross chromosomal rearrangements at an increased rate when comparedwith non-DRT/DMC chromosomes. These results indicate that theDRT/DMC phenotype is not the result of a stochastic processthat could occur at any translocation breakpoint or as an epigeneticresponse to chromosome damage. Instead, our data indicate thatthe replication timing of certain derivative chromosomes isregulated by a cis-acting mechanism that delays both initiationand completion of DNA synthesis along the entire length of thechromosome. Because chromosomes with DRT/DMC are common in tumorcells and in cells exposed to ionizing radiation, we proposethat DRT/DMC represents a common mechanism responsible for thegenomic instability found in cancer cells and for the persistentchromosomal instability associated with cells exposed to ionizingradiation.