Biomedical subjects

Michela Clerici

Publications and source records attributed to Michela Clerici.

6 recordsLinked to original sources

PubMed2006

The Saccharomyces cerevisiae Sae2 protein negatively regulates DNA damage checkpoint signalling.

Double-strand breaks (DSBs) elicit a DNA damage response, resulting in checkpoint-mediated cell-cycle delay and DNA repair. The Saccharomyces cerevisiae Sae2 protein is known to act together with the MRX complex in meiotic DSB processing, as well as in DNA damage response during the mitotic cell cycle. Here, we report that cells lacking Sae2 fail to turn off both Mec1- and Tel1-dependent checkpoints activated by a single irreparable DSB, and delay Mre11 foci disassembly at DNA breaks, indicating that Sae2 may negatively regulate checkpoint signalling by modulating MRX association at damaged DNA. Consistently, high levels of Sae2 prevent checkpoint activation and impair MRX foci formation in response to unrepaired DSBs. Mec1- and Tel1-dependent Sae2 phosphorylation is necessary for these Sae2 functions, suggesting that the two kinases, once activated, may regulate checkpoint switch off through Sae2-mediated inhibition of MRX signalling.

Blotting, Western↗

PubMed2006

The cellular response to chromosome breakage.

DNA double-strand breaks (DSBs) are among the most deleterious types of damage that can occur in the genome of eukaryotic cells because failure to repair them can lead to loss of genetic information and chromosome rearrangements. DSBs can arise by failures in DNA replication and by exposure to environmental factors, such as ionizing radiations and radiomimetic chemicals. Moreover, they might arise when telomeres undergo extensive erosion, leading to the activation of the DNA damage response pathways and the onset of apoptosis and/or senescence. Importantly, DSBs can also form in a programmed manner during development. For example, meiotic recombination and rearrangement of the immunoglobulin genes in lymphocytes require the generation of site- or region-specific DSBs through the action of specific endonucleases. Efficient DSB repair is crucial in safeguarding genome integrity, whose maintenance in the face of DSBs involves branched signalling networks that switch on DNA damage checkpoints, activate DNA repair, induce chromatin reorganization and modulate numerous cellular processes. Not surprisingly, defects in these networks result in a variety of diseases ranging from severe genetic disorders to cancer predisposition and accelerated ageing.

Animals↗

PubMed2005

The Saccharomyces cerevisiae Sae2 protein promotes resection and bridging of double strand break ends.

When eukaryotic chromosomes undergo double strand breaks (DSBs), several evolutionarily conserved proteins, among which the MRX complex, are recruited to the break site, leading to checkpoint activation and DNA repair. The function of the Saccharomyces cerevisiae Sae2 protein, which is known to work together with the MRX complex in meiotic DSB processing and in specific mitotic DSB repair events, is only beginning to be elucidated. Here we provide new insights into the role of Sae2 in mitotic DSB repair. We show that repair by single strand annealing of a single DSB, which is generated by the HO endonuclease between direct repeats, is defective both in the absence of Sae2 and in the presence of the hypomorphic rad50s allele altering the Rad50 subunit of MRX. Moreover, SAE2 overexpression partially suppresses the rad50s single strand annealing repair defects, suggesting that the latter might arise from defective MRX-Sae2 interactions. Finally, SAE2 deletion slows down resection of an HO-induced DSB and impairs DSB end bridging. Thus, Sae2 participates in DSB single strand annealing repair by ensuring both resection and intrachromosomal association of the broken ends.

Alleles↗

PubMed2004

Telomeres and DNA damage checkpoints.

In all eukaryotic organisms, interruptions in duplex DNA molecules elicit a DNA damage response, which includes activation of DNA repair machineries and surveillance mechanisms, known as DNA damage checkpoints. Telomeres and double-strand breaks (DSBs) share the common feature of being physical ends of chromosomes. However, unlike DSBs, telomeres do not activate the DNA damage checkpoints and are usually protected from end-to-end fusions and other processing events that normally promote repair of DNA breaks. This indicates that they are shielded from being recognized and processed as DSBs. On the other hand, chromosome ends resemble damaged DNA, as several factors required for DNA repair and checkpoint networks play important roles in telomere length maintenance. Due to the critical role of both DNA damage checkpoints and telomere homeostasis in maintaining genetic stability and in counteracting cancer development, the knowledge of their interconnections is essential for our understanding of these key cellular controls.

DNA Damage↗

PubMed2004

A Tel1/MRX-dependent checkpoint inhibits the metaphase-to-anaphase transition after UV irradiation in the absence of Mec1.

In Saccharomyces cerevisiae, Mec1/ATR plays a primary role in sensing and transducing checkpoint signals in response to different types of DNA lesions, while the role of the Tel1/ATM kinase in DNA damage checkpoints is not as well defined. We found that UV irradiation in G(1) in the absence of Mec1 activates a Tel1/MRX-dependent checkpoint, which specifically inhibits the metaphase-to-anaphase transition. Activation of this checkpoint leads to phosphorylation of the downstream checkpoint kinases Rad53 and Chk1, which are required for Tel1-dependent cell cycle arrest, and their adaptor Rad9. The spindle assembly checkpoint protein Mad2 also partially contributes to the G(2)/M arrest of UV-irradiated mec1Delta cells independently of Rad53 phosphorylation and activation. The inability of UV-irradiated mec1Delta cells to undergo anaphase can be relieved by eliminating the anaphase inhibitor Pds1, whose phosphorylation and stabilization in these cells depend on Tel1, suggesting that Pds1 persistence may be responsible for the inability to undergo anaphase. Moreover, while UV irradiation can trigger Mec1-dependent Rad53 phosphorylation and activation in G(1)- and G(2)-arrested cells, Tel1-dependent checkpoint activation requires entry into S phase independently of the cell cycle phase at which cells are UV irradiated, and it is decreased when single-stranded DNA signaling is affected by the rfa1-t11 allele. This indicates that UV-damaged DNA molecules need to undergo structural changes in order to activate the Tel1-dependent checkpoint. Active Clb-cyclin-dependent kinase 1 (CDK1) complexes also participate in triggering this checkpoint and are required to maintain both Mec1- and Tel1-dependent Rad53 phosphorylation, suggesting that they may provide critical phosphorylation events in the DNA damage checkpoint cascade.

Anaphase↗

PubMed2003

The S-phase checkpoint and its regulation in Saccharomyces cerevisiae.

Cells are never more vulnerable than during DNA replication, which represents a major moment of potential genetic instability. Genotoxic insults induce many different forms of DNA damage that may interfere with the ability of cells to properly duplicate their genome. Primary damage may in turn undergo structural transformations during DNA replication, thus generating secondary lesions that may be even more dangerous. Cells experiencing replication of damaged DNA or replication blocks activate an S-phase checkpoint response that assures the fidelity and completion of DNA replication before cells enter M-phase. The S-phase checkpoint pathway regulates not only progress through the cell cycle but also DNA repair and DNA replication itself.

DNA Damage↗