Biology subjects

Machin, F.

Publications and source records attributed to Machin, F..

9 recordsLinked to original sources

bioRxiv2026

Msc1 accumulates at and excludes nuclear pore complexes from nucleus-vacuole junctions.

Msc1 is a yeast nuclear envelope (NE) protein that facilitates DNA double-strand break repair. In its absence, cells exhibit abnormal nuclear morphologies and maldistribution of nuclear pore complexes (NPCs). Msc1 is not uniformly distributed across the NE but concentrates onto dynamic patches that often coincide with blebs or herniations. Here, we report that Msc1 abundance and the number of patches dramatically increase after the diauxic shift. Msc1 patches are devoid of NPCs and fully colocalize with nucleus-vacuole junctions (NVJs), which are involved in piecemeal micronucleophagy. In the absence of Msc1, abnormal NPC aggregates accumulate adjacent to vacuoles, both at and outside the NE. We conclude that Msc1 is the key factor that maintains NPC homeostasis as cells prepare to enter quiescence.

cell biology↗

bioRxiv2024

Continuous nuclear envelope surveillance is required for DNA double-strand break repair.

Precise double-strand break (DSB) repair is paramount for genome stability. Homologous recombination (HR) is preferred to repair DSBs when a nearby sister chromatid ensures an error-free template. In Saccharomyces cerevisiae, this preference extends into anaphase and telophase (late mitosis; late-M), despite sister chromatids having been pulled apart. Previously, we identified the nuclear envelope (NE) protein Msc1 as important for late-M DSB repair. Here, we report that Msc1 faces the NE lumen, and its depletion leads to DSB-independent over-compartmentalization of the nucleus, which hampers approximation of sister loci after DSB. Depletion of Msc1 also leads to nuclear pore complex mislocation, a phenotype shared by the highly conserved NE healing complex ESCRT-III. Critically, we show that both Msc1 and ESCRT-III also ensure DSB repair in G2/M, and that there is synergism between Msc1 and the ESCRT-III subunit Snf7. These findings highlight the essential role of NE health in DSB repair.

cell biology↗

bioRxiv2023

Msc1 is a nuclear envelope protein that reinforces DNA repair in late mitosis.

Precise double-strand break (DSB) repair is paramount for genome stability. Homologous recombination (HR) repairs DSBs when cyclin-dependent kinase (CDK) activity is high, which correlates with the availability of the sister chromatid as a template. However, anaphase and telophase are paradoxical scenarios since high CDK favors HR despite sister chromatids being no longer aligned. To identify factors specifically involved in DSB repair in late mitosis, we have undertaken comparative proteomics in Saccharomyces cerevisiae and found that Msc1, a poorly characterized nuclear envelope protein, is significantly enriched upon both random and guided DSBs. We further show that {Delta}msc1 is more sensitive to DSBs in late mitosis, and has a delayed repair of DBSs, as indicated by increased Rad53 hyperphosphorylation, fewer Rad52 repair factories, and slower HR completion. We discuss how Msc1 may favor the formation of Rad52 factories and the timely completion of HR before cytokinesis.

molecular biology↗

bioRxiv2023

Cohesin still drives homologous recombination repair of DNA double-strand breaks in late mitosis.

The cohesin complex maintains sister chromatid cohesion from S phase to anaphase onset. Cohesin also plays roles in chromosome structure and DNA repair. At anaphase onset, the cohesin subunit Scc1 is cleaved to allow segregation in an orderly manner, although some residual cohesin subunits remain to maintain chromosome structure. Efficient DNA double strand break (DSB) repair by homologous recombination (HR) with the sister chromatid also depends on cohesin. Here, we have examined the role of residual cohesin in DSB repair in telophase (late mitosis). We have found that Scc1 returns in telophase after DSBs, and that it partially reconstitutes a chromatin-bound cohesin complex with Smc1 and an acetylated pool of Smc3 after a single HO-induced DSB at the MAT locus. However, this new cohesin is neither required for the HR-driven MAT switching nor binds to the MAT locus after the DSB.

molecular biology↗

bioRxiv2021

Nuclear envelope reshaping around the vacuole determines the morphology of the ribosomal DNA

The ribosomal DNA array (rDNA) of Saccharomyces cerevisiae has served as a model to address chromosome organization. In cells arrested before anaphase (mid-M), the rDNA acquires a highly structured chromosomal organization referred to as the rDNA loop, whose length can double the cell diameter. Previous works established that complexes such as condensin and cohesin are essential to attain this structure. Here, we report that the rDNA loop adopts distinct morphologies that arise as spatial adaptations to changes in the nuclear morphology triggered during the mid-M arrests. Interestingly, the formation of the rDNA loop results in the appearance of a space under the loop (SUL) which is devoid of any nuclear component yet colocalizes with the vacuole. We finally show that the formation and maintenance of the rDNA loop and the SUL require TORC1 and membrane synthesis. We propose that the rDNA-associated nuclear envelope (NE) reshapes into a loop to accommodate the vacuole, with the nucleus becoming bilobed.

cell biology↗

bioRxiv2020

Topoisomerase II deficiency leads to a postreplicative structural shift in all Saccharomyces cerevisiae chromosomes.

The key role of Topoisomerase II (Top2) is the removal of topological intertwines between sister chromatids. In yeast, inactivation of Top2 brings about distinct cell cycle responses. In the case of the conditional top2-5 allele, interphase and mitosis progress on schedule but cells suffer from a segregation catastrophe. We here show that top2-5 chromosomes fail to enter a Pulsed-Field Gel Electrophoresis (PFGE) in the first cell cycle, a behavior traditionally linked to the presence of replication and recombination intermediates. We distinguished two classes of affected chromosomes: the rDNA-bearing chromosome XII, which fails to enter a PFGE at the beginning of S-phase, and all the other chromosomes, which fail at a postreplicative stage. In synchronously cycling cells, this late PFGE retention is observed in anaphase; however, we demonstrate that this behavior is independent of cytokinesis, stabilization of anaphase bridges, spindle pulling forces and even anaphase onset. Strikingly, once the PFGE retention has occurred it becomes refractory to Top2 re-activation. DNA combing, two-dimensional electrophoresis, genetic analyses and GFP-tagged DNA damage markers suggest that non-recombinational modifications of late replication intermediates may account for the shift in the PFGE behavior. The fact that this shift does not trigger G2/M checkpoints further supports this statement since checkpoints are active for other replicative stresses in the absence of Top2. We propose that the prolonged absence of Top2 activity leads to a general chromosome structural change. This change might interlock chromatids together with catenations and thus contribute to the formation of anaphase bridges in top2 mutants.

molecular biology↗

bioRxiv2019

Cytological and genetic consequences for the progeny of a mitotic catastrophe provoked by Topoisomerase II deficiency.

Topoisomerase II (Top2) removes topological linkages between replicated chromosomes. Top2 inhibition leads to mitotic catastrophe (MC) when cells unsuccessfully try to split their genetic material between the two daughter cells. Herein, we have characterized the fate of these daughter cells in the budding yeast. Clonogenic and microcolony experiments, in combination with vital and apoptotic stains, showed that 75% of daughter cells become senescent in the short term; they are unable to divide but remain alive. Decline in cell vitality then occurred, yet slowly, uncoordinatedly when comparing pairs of daughters, and independently of the cell death mediator Mca1/Yca1. Furthermore, we showed that senescence can be modulated by ploidy, suggesting that gross chromosome imbalances during segregation may account for this phenotype. Indeed, we found that diploid long-term survivors of the MC are prone to genomic imbalances such as trisomies, uniparental disomies and terminal loss of heterozygosity (LOH), the latter affecting the longest chromosome arms.

cell biology↗

bioRxiv2018

DNA damage in telophase leads to coalescence between segregated sister chromatid loci.

The generation of DNA double strand breaks (DSBs) pose a high risk for the maintenance of the genome. Cells repair DSBs through two major mechanisms: non-homologous end joining (NHEJ) and homologous recombination (HR). HR is usually preferred when a sister chromatid is available, thus cells have coupled the activity of the cycling dependent kinase (CDK) to the selection of HR (Symington et al. 2014). Paradoxically, there is a window in the cell cycle where CDK is high despite a sister chromatid is not physically available for HR: late anaphase/telophase. We have here studied in budding yeast the response to DSBs generated in telophase by means of the radiomimetic drug phleomycin. We first show that phleomycin treatment activates the DNA damage response and leads to a delay in the telophase-to-G1 transition. Outstandingly, we also found a partial reversion of sister chromatid segregation, which includes approximation of spindle pole bodies (SPBs) and sister centromeres, de novo formation of anaphase bridges, trafficking of DNA back and forth through the cytokinetic plane and events of coalescence between segregated sister telomeres. We importantly show that phleomycin promotes a massive change in the structure and dynamic of mitotic microtubules (MTs), which coincides with dephosphorylation and re-localization of kinesin-5 Cin8. We propose that anaphase is not entirely irreversible and that there could still be a window to repair DSBs using the sister chromatid after segregation.

cell biology↗

bioRxiv2017

Genome-scale genetic interactions position the Mitotic Exit Network as a major antagonist of transient Topoisomerase II deficiency.

Topoisomerase II (Top2) is the essential protein that resolves DNA catenations. When the Top2 is inactivated, mitotic catastrophe results from massive entanglement of chromosomes. Top2 is also the target of many first-line anticancer drugs, the so-called Top2 poisons. Often, tumours become resistant to these drugs by downregulating Top2. Here, we have compared two isogenic yeast strains carrying top2 thermosensitive alleles that differ in their resistance to Top2 poisons, the broadly-used poison-sensitive top2-4 and the poison-resistant top2-5. We found that top2-5 transits through anaphase faster than top2-4. In order to define the biological importance of this difference, we performed genome-scale Synthetic Gene Array (SGA) analyses during chronic sublethal Top2 downregulation and acute, yet transient, Top2 inactivation. We find that downregulation of cell cycle progression, especially the Mitotic Exit Network (MEN), protects against Top2 deficiency. In all conditions, genetic protection was stronger in top2-5, and this correlated with destabilization of anaphase bridges by execution of MEN. We suggest that mitotic exit may be a therapeutic target to hypersensitize cancer cells carrying downregulating mutations in TOP2.

genetics↗