Cell Biology of Mitotic Recombination

Abstract

Homologous recombination provides high-fidelity DNA repair throughout all domains of life. Live cell fluorescence microscopy offers the opportunity to image individual recombination events in real time providing insight into the in vivo biochemistry of the involved proteins and DNA molecules as well as the cellular organization of the process of homologous recombination. Herein we review the cell biological aspects of mitotic homologous recombination with a focus on Saccharomyces cerevisiae and mammalian cells, but will also draw on findings from other experimental systems. Key topics of this review include the stoichiometry and dynamics of recombination complexes in vivo, the choreography of assembly and disassembly of recombination proteins at sites of DNA damage, the mobilization of damaged DNA during homology search, and the functional compartmentalization of the nucleus with respect to capacity of homologous recombination.

Regulation of Recombination and Genomic Maintenance

“…The discovery that RAD51 and other HR proteins assemble into microscopically visible foci in response the DNA damage paired with genetic analysis enabled to develop a spatiotemporal "choreographic" view of HR as brilliantly discussed by Lisby and Rothstein (2015). The single-cell resolution complements the analysis of genetic endpoints, such as survival or recombination rates and in vivo biochemical approaches, demonstrating that not only assembly but also disassembly of HR intermediates is critical (Symington and Heyer 2006).…”

“…In particular, the Smc5 -Smc6 complex plays an essential role in HR, which is currently poorly understood Torres-Rosell et al 2007;Copsey et al 2013;Xaver et al 2013). As discussed by Lisby and Rothstein (2015), the cell biological analysis of HR is still in its early stages and full of promise to elucidate the mechanisms controlling HR dynamics and its spatial control.…”

“…2) (Bermejo et al 2012). New optical and cell biological techniques discussed by Lisby and Rothstein (2015) will further push the resolution limit and provide insights into HR in specific nuclear subcompartments, such as heterochromatin (see above).…”

Nonhomologous DNA end-joining for repair of DNA double-strand breaks

“…1). In late S and G2, HR is another major pathway for DSB repair, relying on more extensive homology tracts as a template for repair (8). When NHEJ is compromised due to the absence of one or more key protein components, the activities of other DNA end joining pathways that typically involve more extensive end resection become apparent.…”

“…Signaling factors appear to be important in controlling resection, as there is evidence that the DNA damage response protein p53-binding protein 1 (53BP1) is antagonistic to end resection, acting through a number of effector proteins (21,22). 53BP1 and mediator of DNA damage checkpoint protein 1 (MDC1) are recruited to DSBs through a number of modified histone residues and appear to have distinct roles in DSB repair (8,23,24). Further work is required to elucidate specifically how 53BP1 recruitment inhibits extensive end resection.…”