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Angela Taddei

Publications and source records attributed to Angela Taddei.

12 recordsLinked to original sources
PubMed2026

Navigating nuclear space: How Rad51 filaments promote long-range homology search during homologous recombination - Lessons from budding yeast.

DNA double-strand breaks (DSBs) threaten genomic integrity, with erroneous repair leading to chromosomal rearrangements and pathologies. In eukaryotes, DSBs are primarily repaired via non-homologous end-joining (NHEJ) or homologous recombination (HR). HR restores genetic information by using an undamaged homologous sequence as a template, a process dependent on Rad51-mediated homology search. This review synthesizes recent advances in our understanding of HR, with a focus on the homology search process in mitotic cells, primarily using Saccharomyces cerevisiae as a model organism. We explore factors that limit recombination efficiency and discuss how Rad51 filament dynamics overcome spatial and temporal challenges imposed by nuclear architecture and chromatin dynamics, to ensure efficient HR. Key insights include the dynamic behavior of Rad51 filaments, which undergo cycles of compaction and extension, thereby optimizing exploration of the nuclear volume and increasing the likelihood of encountering distant homologous sequences. The interplay between long-range resection, filament elongation, and nuclear constraints further shapes the search process, balancing the need for extensive exploration with the risks of excessive DNA degradation and ectopic recombination. Collectively, these findings support an integrated model in which the efficiency and accuracy of homologous recombination are governed by regulated Rad51 filament dynamics and the constraints imposed by nuclear architecture.

Rad51 Recombinase↗
PubMed2006

In and out of the replication factory.

In this issue of Cell, use live-fluorescence microscopy to monitor individual genomic loci as they replicate in budding yeast. They confirm that DNA is recruited to replication factories and show that sister replication forks initiated from the same origin are held together within a single replication factory.

DNA Replication↗
PubMed2006

Nuclear pore association confers optimal expression levels for an inducible yeast gene.

The organization of the nucleus into subcompartments creates microenvironments that are thought to facilitate distinct nuclear functions. In budding yeast, regions of silent chromatin, such as those at telomeres and mating-type loci, cluster at the nuclear envelope creating zones that favour gene repression. Other reports indicate that gene transcription occurs at the nuclear periphery, apparently owing to association of the gene with nuclear pore complexes. Here we report that transcriptional activation of a subtelomeric gene, HXK1 (hexokinase isoenzyme 1), by growth on a non-glucose carbon source led to its relocalization to nuclear pores. This relocation required the 3' untranslated region (UTR), which is essential for efficient messenger RNA processing and export, consistent with an accompanying report. However, activation of HXK1 by an alternative pathway based on the transactivator VP16 moved the locus away from the nuclear periphery and abrogated the normal induction of HXK1 by galactose. Notably, when we interfered with HXK1 localization by either antagonizing or promoting association with the pore, transcript levels were reduced or enhanced, respectively. From this we conclude that nuclear position has an active role in determining optimal gene expression levels.

3' Untranslated Regions↗
PubMed2006

Repairing subtelomeric DSBs at the nuclear periphery.

Nuclear organization creates microenvironments favoring distinct nuclear functions. In budding yeast, silent chromatin regions such as telomeres are clustered at the nuclear periphery, creating zones of transcriptional repression. Recently, in the Journal of Cell Biology, Therizols et al. report that "telomere tethering at the nuclear periphery is essential for DNA double strand break repair in subtelomeric regions". Here, we discuss these results and their functional implications.

Animals↗
PubMed2005

Temporal separation of replication and recombination requires the intra-S checkpoint.

In response to DNA damage and replication pausing, eukaryotes activate checkpoint pathways that prevent genomic instability by coordinating cell cycle progression with DNA repair. The intra-S-phase checkpoint has been proposed to protect stalled replication forks from pathological rearrangements that could result from unscheduled recombination. On the other hand, recombination may be needed to cope with either stalled forks or double-strand breaks resulting from hydroxyurea treatment. We have exploited fission yeast to elucidate the relationship between replication fork stalling, loading of replication and recombination proteins onto DNA, and the intra-S checkpoint. Here, we show that a functional recombination machinery is not essential for recovery from replication fork arrest and instead can lead to nonfunctional fork structures. We find that Rad22-containing foci are rare in S-phase cells, but peak in G2 phase cells after a perturbed S phase. Importantly, we find that the intra-S checkpoint is necessary to avoid aberrant strand-exchange events during a hydroxyurea block.

Cell Survival↗
PubMed2005

The effects of histone deacetylase inhibitors on heterochromatin: implications for anticancer therapy?

Histone acetylation regulates many chromosome functions, such as gene expression and chromosome segregation. Histone deacetylase inhibitors (HDACIs) induce growth arrest, differentiation and apoptosis of cancer cells ex vivo, as well as in vivo in tumour-bearing animal models, and are now undergoing clinical trials as anti-tumour agents. However, little attention has been paid to how HDACIs function in these biological settings and why different cells respond in different ways. Here, we discuss the consequences of inhibiting histone deacetylases in cycling versus non-cycling cells, in light of the dynamics of histone acetylation patterns with a specific emphasis on heterochromatic regions of the genome.

Cell Cycle↗
PubMed2005

Multiple pathways tether telomeres and silent chromatin at the nuclear periphery: functional implications for sir-mediated repression.

The positioning of chromosomal domains within interphase nuclei is thought to contribute to establishment and maintenance of epigenetic control. Using GFP-tagged chromosomal domains, LexA-fusion targeting and live microscopy, we investigated mechanisms through which chromatin can be anchored to the nuclear envelope (NE). We find that a subdomain of the silencing information regulator Sir4 (Sir4(PAD)) and yKu80 are sufficient to tether a chromatin region to the nuclear periphery, independently of their silencing function. Sir4(PAD) interacts with Esc1 (Establishes Silent Chromatin 1), a large acidic protein, localized at the nuclear periphery in the absence of Sir4 and yKu. Sir4 also binds to the periphery through yKu80, whose perinuclear ligand is unidentified. Both pathways are involved in the localization of natural telomeres. To show that silent chromatin can also mediate anchorage, we uncoupled the HMR silent mating-type locus from the chromosome using inducible site-specific recombination. Real-time cytological techniques reveal the position and dynamics of the excised locus. We show that the silent HMR ring associates with the NE in a SIR-dependent manner, while derepressed excised rings move without detectable constraint throughout the nucleoplasm. Dual anchoring pathways thus cooperate to generate high concentrations of SIR proteins in perinuclear foci, which in turn promote repression.

Cell Nucleus↗
PubMed2004

Separation of silencing from perinuclear anchoring functions in yeast Ku80, Sir4 and Esc1 proteins.

In budding yeast, the nuclear periphery forms a subcompartment in which telomeres cluster and SIR proteins concentrate. To identify the proteins that mediate chromatin anchorage to the nuclear envelope, candidates were fused to LexA and targeted to an internal GFP-tagged chromosomal locus. Their ability to shift the locus from a random to a peripheral subnuclear position was monitored in living cells. Using fusions that cannot silence, we identify YKu80 and a 312-aa domain of Sir4 (Sir4(PAD)) as minimal anchoring elements, each able to relocalize an internal chromosomal locus to the nuclear periphery. Sir4(PAD)-mediated tethering requires either the Ku complex or Esc1, an acidic protein that is localized to the inner face of the nuclear envelope even in the absence of Ku, Sir4 or Nup133. Finally, we demonstrate that Ku- and Esc1-dependent pathways mediate natural telomere anchoring in vivo. These data provide the first unambiguous identification of protein interactions that are both necessary and sufficient to localize chromatin to the nuclear envelope.

Alleles↗
PubMed2004

The function of nuclear architecture: a genetic approach.

Eukaryotic genomes are distributed on linear chromosomes that are grouped together in the nucleus, an organelle separated from the cytoplasm by a characteristic double membrane studded with large proteinaceous pores. The chromatin within chromosomes has an as yet poorly characterized higher-order structure, but in addition to this, chromosomes and specific subchromosomal domains are nonrandomly positioned in nuclei. This review examines functional implications of the long-range organization of the genome in interphase nuclei. A rigorous test of the physiological importance of nuclear architecture is achieved by introducing mutations that compromise both structure and function. Focussing on such genetic approaches, we address general concepts of interphase nuclear order, the role of the nuclear envelope (NE) and lamins, and finally the importance of spatial organization for DNA replication and heritable gene expression.

Animals↗
PubMed2002

Higher-order structure in pericentric heterochromatin involves a distinct pattern of histone modification and an RNA component.

Post-translational modification of histone tails is thought to modulate higher-order chromatin structure. Combinations of modifications including acetylation, phosphorylation and methylation have been proposed to provide marks recognized by specific proteins. This is exemplified, in both mammalian cells and fission yeast, by transcriptionally silent constitutive pericentric heterochromatin. Such heterochromatin contains histones that are generally hypoacetylated and methylated by Suv39h methyltransferases at lysine 9 of histone H3 (H3-K9). Each of these modification states has been implicated in the maintenance of HP1 protein-binding at pericentric heterochromatin, in transcriptional silencing and in centromere function. In particular, H3-K9 methylation is thought to provide a marking system for the establishment and maintenance of stably repressed regions and heterochromatin subdomains. To address the question of how these two types of modifications, as well as other unidentified parameters, function to maintain pericentric heterochromatin, we used a combination of histone deacetylase inhibitors, RNAse treatments and an antibody raised against methylated branched H3-K9 peptides. Our results show that both H3-K9 acetylation and methylation can occur on independent sets of H3 molecules in pericentric heterochromatin. In addition, we identify an RNA- and histone modification-dependent structure that brings methylated H3-K9 tails together in a specific configuration required for the accumulation of HP1 proteins in these domains.

Fluorescent Antibody Technique↗