Chromatinbridges: stochastic breakage or regulated resolution? Genetic material is organized in the form of chromosomes, which need to be segregated accurately into two daughter cells in each cell cycle. However, chromosome fusion or the presence of unresolved interchromosomal linkages lead to the formation of chromatinbridges, which can induce DNA lesions and genome instability. Persistent chromatinbridges are trapped in the cleavage furrow and are broken at or after abscission, the final step of cytokinesis. In this review, we focus on recent progress in understanding the mechanism of bridge breakage and resolution. We discuss the molecular machinery and enzymes that have been implicated in the breakage and processing of bridge DNA. In addition, we outline both the immediate outcomes
LEM-3 is a midbody-tethered DNA nuclease that resolves chromatinbridges during late mitosis Faithful chromosome segregation and genome maintenance requires the removal of all DNA bridges that physically link chromosomes before cells divide. Using C. elegans embryos we show that the LEM-3/Ankle1 nuclease defines a previously undescribed genome integrity mechanism by processing DNA bridges right before cells divide. LEM-3 acts at the midbody, the structure where abscission occurs at the end of cytokinesis. LEM-3 localization depends on factors needed for midbody assembly, and LEM-3 accumulation is increased and prolonged when chromatinbridges are trapped at the cleavage plane. LEM-3 locally processes chromatinbridges that arise from incomplete DNA replication, unresolved recombination
Breakage in breakage-fusion-bridge cycle: an 80-year-old mystery. 2021 marked the 80th anniversary of Barbara McClintock's pioneering article on the breakage-fusion-bridge (BFB) cycle. Of the three steps of the BFB cycle, breakage remains the least understood despite its major contribution to mutagenesis. We discuss recent findings shedding light on how chromatinbridges break in yeast and animal
condensation, augmented anaphase chromatin-bridge formation, and micronuclei in daughter cells of proband skin fibroblasts. To test the functional relevance of the discovered variants, we generated an ncapg2 zebrafish model. Morphants displayed clinically relevant phenotypes, such as renal anomalies, microcephaly, and concomitant increases in apoptosis and altered mitotic progression. These could be rescued
knockout cancer cell line models. Single DNA fiber analysis showed that ATR inhibition does not exacerbate replication fork degradation. Instead, we find ATR inhibitors accelerate mitotic entry, resulting in the formation of chromatinbridges and lagging chromosomes. Furthermore, using genome-wide single-cell sequencing, we show that ATR inhibition enhances genomic instability of olaparib-treated BRCA2
, and, as occurs upon RZZ inhibition, loss of NUD-2 delays the formation of load-bearing kinetochore-microtubule attachments and causes chromatinbridges in anaphase. Survival of embryos requires a functional SAC, and kinetochores without NUD-2 recruit an excess of SAC proteins. Consistent with this, SAC signaling in early embryos extends mitotic duration and prevents high rates of chromosome mis-segregation
with a reduction in chiasma frequency. Finally, the presence of chromatinbridges indicates the indirect occurrence of chromosomal inversions, although chromosome fragments were not clearly recognized. Possible reasons for such meiotic abnormalities and the large prevalence of bivalent formation are discussed.
and mus-81 mutants, the respective double mutants displaying 100% embryonic lethality. The combined loss of LEM-3 and MUS-81 leads to altered processing of recombination intermediates, a delayed disassembly of foci associated with CO designated sites, and the formation of univalents linked by SPO-11 dependent chromatinbridges (dissociated bivalents). However, LEM-3 foci do not colocalize with ZHP-3 , a marker that congresses into CO designated sites. In addition, neither CO frequency nor distribution is altered in lem-3 single mutants or in combination with mus-81 or slx-4 mutations. Finally, we found persistent chromatinbridges during meiotic divisions in lem-3; slx-4 double mutants. Supported by the localization of LEM-3 between dividing meiotic nuclei, this data suggest that LEM-3 is able
that engages the abscission checkpoint (NoCut) in response to mitotic problems such as persisting chromatinbridges within the midbody. Importantly, a human polymorphism in CHMP4C (rs35094336, CHMP4C) increases cancer susceptibility. Here, we explain the structural and functional basis for this cancer association: The CHMP4C allele unwinds the C-terminal helix of CHMP4C, impairs binding to the early-acting
numbers of chromatinbridges in Nesprin-2 knockdown cells in anaphase. Thus, Nesprin-2 may have an impact on chromosomes which might be due to its interaction with condensins or to indirect mechanisms provided by its interactions at the nuclear envelope.
that Boi1/2 are required for a late step in the fusion of secretory vesicles with the plasma membrane of the growing bud. Cells lacking Boi1/2 accumulate secretory vesicles and are defective in bud growth. In contrast, Boi2 is specifically required for abscission inhibition in cells with chromatinbridges. The SH3 domain of Boi2, which is dispensable for bud growth and targets Boi2 to the site at sites of polarized growth, and acts as an abscission inhibitor during cytokinesis in response to chromatinbridges.
Never tear us a-PARP: Dealing with DNA lesions during mitosis Tumors defective in homologous recombination (HR) are highly sensitive to poly ADP-ribose polymerase (PARP) inhibition, however the cell biological mechanisms underlying this synthetic lethality remain elusive. We recently identified that PARP inhibitor-induced DNA lesions persist until mitosis, subsequently causing mitotic chromatinbridges, multinucleation and apoptosis. Here, we discuss the implications of these findings.
induces cytotoxicity in HR-deficient cancer cells is incomplete. Here we find PARP inhibition to compromise replication fork stability in HR-deficient cancer cells, leading to mitotic DNA damage and consequent chromatinbridges and lagging chromosomes in anaphase, frequently leading to cytokinesis failure, multinucleation and cell death. PARP-inhibitor-induced multinucleated cells fail clonogenic
Rebuilding Chromosomes After Catastrophe: Emerging Mechanisms of Chromothripsis Cancer genome sequencing has identified chromothripsis, a complex class of structural genomic rearrangements involving the apparent shattering of an individual chromosome into tens to hundreds of fragments. An initial error during mitosis, producing either chromosome mis-segregation into a micronucleus or chromatinbridge interconnecting two daughter cells, can trigger the catastrophic pulverization of the spatially isolated chromosome. The resultant chromosomal fragments are religated in random order by DNA double-strand break repair during the subsequent interphase. Chromothripsis scars the cancer genome with localized DNA rearrangements that frequently generate extensive copy number alterations, oncogenic gene
a mean-field theory from which we obtain a scaling relation between the typical cluster size and the protein switching rate. Protein switching also reshapes intrachromatin contacts to give networks resembling those seen in topologically associating domains, as switching markedly favors local (short-range) contacts over distant ones. Our results point to posttranslational modification of chromatin -bridging proteins as a generic mechanism driving the self-assembly of highly dynamic, nonequilibrium, protein clusters with the properties of nuclear bodies.
of PICH SIMs during mitosis. Although all SIMs are dispensable for PICH's localization on ultrafine anaphase DNA bridges, only SIM3 (third SIM, close to the C-terminus end of PICH) is critical for its centromeric localization. Intriguingly, the other 2 SIMs function in chromatinbridge prevention. With these results, we propose a novel SUMO-dependent regulation of PICH's function on mitotic centromeres.
Characterization of the NTPR and BD1 interacting domains of the human PICH–BEND3 complex Chromosome integrity depends on DNA structure-specific processing complexes that resolve DNA entanglement between sister chromatids. If left unresolved, these entanglements can generate either chromatinbridging or ultrafine DNA bridging in the anaphase of mitosis. These bridge structures are defined
USP19 deubiquitinates HDAC1/2 to regulate DNA damage repair and control chromosomal stability Excessive accumulation of DNA damage will generate chromosome stress, leading to various chromosome abnormalities such as chromatinbridge and result in genomic instability. Orchestra procession and regulation of DNA damage repair are vital for keeping genome stability. Despite of the key role of HDAC1/2
that biallelic mutations in NCAPD2, NCAPH, or NCAPD3, encoding subunits of these complexes, cause microcephaly. In addition, hypomorphic Ncaph2 mice have significantly reduced brain size, with frequent anaphase chromatinbridge formation observed in apical neural progenitors during neurogenesis. Such DNA bridges also arise in condensin-deficient patient cells, where they are the consequence of failed sister