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Maria Jasin: Overview

Homologous Recombination as a Major DNA Repair Pathway in Mammalian Cells

Post-doctoral fellow Christine Richardson has demonstrated that mouse chromosomes 17 (red) and 14 (green) can be induced to recombine with each other when a double-strand break is introduced into one of them.

Homologous recombination has long been recognized as an important DSB repair pathway in model organisms, such as E. coli and yeast. By contrast, in mammalian cells, alternative nonhomologous processes were presumed to repair DSBs. We challenged this presumption by performing experiments in which we generated a single DSB in the genome of a mammalian cell line and then examined repair. These experiments conclusively demonstrated that homologous repair is a major repair pathway in mammalian cells.

Homologous recombination is stimulated in the range of 3 orders of magnitude by a break in the chromosome; and nearly half of the total repair events arise from homologous repair (Liang et al. Proc Natl Acad Sci USA. 1998). These experiments also confirmed an important role for nonhomologous repair, as had been predicted. We expect that use of the 2 pathways may differ in different cell types, depending on specific parameters (such as whether cells are cycling or resting).

Our long-term goals are to exploit the molecular genetic systems we have developed to understand the role of homologous recombination in maintaining genetic stability. We are determining factors that govern “partner choice” — i.e., the choice of which 2 DNA molecules recombine — as well as the protein components involved in the repair process. Meiotic (and germline) recombination is also a key interest, and we maintain a strong interest in developing technologies both to facilitate studies of DNA repair and to manipulate genomes. With these goals, we hope to contribute to the understanding of human disease, and potentially to its reversal, through genetic correction.