Mechanisms of Recombination between Diverged Sequences in Wild-Type and BLM-Deficient Mouse and Human Cells

Abstract

Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged (“homeologous”) sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally ≤100 bp, even in Msh2^−/− cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.

Supplemental material for this article may be found at http://mcb.asm.org/.

This work was supported by grants R01GM54668 from the NIH and NSF0346354 from the National Science Foundation to M.J. J.R.L. was supported by NRSA Postdoctoral Fellowship F32GM084637 from the NIH.

We are grateful to the Jasin lab for helpful commentary regarding experimental design and analysis and to Kyoji Horie and Kosuke Yusa for providing the Blm^tet/tet ES cells and Nathan Ellis and Karen Ouyang for providing human fibroblast cell lines.