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Rad9, a 53BP1 Ortholog of Budding Yeast, Is Insensitive to Spo11-Induced Double-Strand Breaks During Meiosis.

ABSTRACT: Exogenous double-strand breaks (DSBs) induce a DNA damage response during mitosis as well as meiosis. The DNA damage response is mediated by a cascade involving Mec1/Tel1 (ATR/ATM) and Rad53 (Chk2) kinases. Meiotic cells are programmed to form DSBs for the initiation of meiotic recombination. In budding yeast, Spo11-mediated meiotic DSBs activate Mec1/Tel1, but not Rad53; however, the mechanism underlying the insensitivity of Rad53 to meiotic DSBs remains largely unknown. In this study, we found that meiotic cells activate Rad53 in response to exogenous DSBs and that this activation is dependent on an epigenetic marker, Dot1-dependent histone H3K79 methylation, which becomes a scaffold of an Rad53 mediator, Rad9, an ortholog of 53BP1. In contrast, Rad9 is insensitive to meiotic programmed DSBs. This insensitiveness of Rad9 derives from its inability to bind to the DSBs. Indeed, artificial tethering of Rad9 to the meiotic DSBs activated Rad53. The artificial activation of Rad53 kinase in meiosis decreases the repair of meiotic DSBs. These results suggest that the suppression of Rad53 activation is a key event in initiating a meiotic program that repairs programmed DSBs.

SUBMITTER: Usui T

PROVIDER: S-EPMC8027355 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In budding yeast, DNA lesions and stalled replication forks are sensed by the apical checkpoint kinase Mec1/ATR, which leads to the downstream activation of the effector kinase Rad53/CHK1. This activation depends on Rad9 and Mrc1, two checkpoint mediators that integrate the nature of the challenge in different phases of the cell cycle. Rad9 mediates the activation of the DNA damage checkpoint throughout the cell cycle, while the function of Mrc1 is restricted to the S phase of the cell cycle, when it travels with the replication fork and activates the DNA replication checkpoint in response to a variety of replication impediments. In this scenario, the role of Rad9 in S phase has been largely disregarded since the discovery of Mrc1, because Rad9 is dispensable for the timely activation of Rad53 in response to the drug hydroxyurea, which halts forks, and is only recruited to those stalled forks when Mrc1 is absent. Thus, Rad9 is simply believed to act as a backup pathway for Mrc1 during replication. We have re-evaluated the role of Rad9 when DNA damage arises during replication and characterized its functional interplay with Mrc1. To this end, we have used genome-wide approaches, single-molecule analysis, pulsed-field and 2D gel electrophoresis, as well as a careful combination of different replication-challenging drugs. We have found that both Mrc1 and Rad9 play distinct but complementary functions in the replication stress response during S phase, for they coordinate the early and late functions of Rad53, respectively. While Mrc1 is responsible for the fast activation of Rad53 in response to fork-halting drugs in order to repress late origins, Rad9 maintains Rad53 in an active state during prolonged fork arrest and is necessary to sustain this response for long periods. Remarkably, we also have found that Rad9 possesses the unprecedented activity of slowing down replication fork progression in response to DNA damage. This work thus restores the legitimate role of Rad9 as a central actor in the maintenance of genome integrity during replication. This has important implications for our understanding of the management of the checkpoint during perturbed replication in human cells, for Rad9 has three orthologues, 53BP1, BRCA1 and MDC1, whose contribution to this aspect of genome integrity remains largely unexplored.

Dataset Information

Rad9, a 53BP1 Ortholog of Budding Yeast, Is Insensitive to Spo11-Induced Double-Strand Breaks During Meiosis.

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