bims-micesi 2025-09-21 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2025–09–21
nineteen papers selected by
Valentina Piano, Uniklinik Köln

BRD4 regulates Aurora B kinase activity.
MoMad2 With a Conserved Function in the Spindle Assembly Checkpoint Is Required for Maintaining Appressorial Turgor Pressure and Pathogenicity of Rice Blast Fungus.
A minimum module for positioning the Chromosomal Passenger Complex at the cell center for cytokinesis.
A distinct phase of cyclin B (Cdc13) nuclear export at mitotic entry in Schizosaccharomyces pombe.
Robust CENP-A incorporation in human cells is independent of transcription and cohesin components.
The conserved machinery of bipolar prospindle formation controls acentrosomal spindle orientation in land plants.
The dynamics of centromere assembly and disassembly during quiescence.
Spindle-localized F-actin regulates polar MTOC organization and the fidelity of meiotic spindle formation.
An electrostatic repulsion model of centromere organisation.
Chromatin Compaction Scaling with Cell Size Follows a Power Law from Interphase Through Mitosis.
The spatial arrangement of chromosomes determines fusion of nucleoli in diploid budding yeast.
The embryonic lethal mutation zyg-10(b261) is an allele of the atx-2 gene and disrupts multiple aspects of early embryogenesis.
Cellular mechanism linking endoplasmic reticulum inheritance and cell cycle regulation of the nuclear genome.
Hydrophobic interactions of FG-nucleoporins are required for dilating nuclear membrane pores into selective transport channels after mitosis.
Polo-Like Kinase 1 Phosphorylation Tunes the Functional Viscoelastic Properties of the Centrosome Scaffold.
CENP-A is diluted during bovine spermatogenesis and is maintained at internally positioned centromere clusters in mature bull sperm.
MLL/WDR5 complex promotes recruitment of KIF2C to midbody to ensure MT depolymerization and furrow initiation during cytokinesis.
Chromosomal instability and genomic alterations in cholangiocarcinoma from Northeastern Thailand.
CRISPR-engineered human GATA2 deficiency model uncovers mitotic dysfunction and premature aging in HSPCs, impairing hematopoietic fitness.

bioRxiv. 2025 Aug 07. pii: 2025.08.06.668960. [Epub ahead of print]

BRD4 regulates Aurora B kinase activity.

Ballachanda N Devaiah, Dan Cheng, Amit K Singh, Dinah S Singer.

BRD4, a pleiotropic regulator of chromatin structure and transcription, plays critical roles in cancer and immune responses. Unlike other transcriptional regulators, BRD4 largely remains bound to chromosomes during early mitosis. Here we report that BRD4 also regulates mitosis through its direct interaction with and phosphorylation of Aurora B kinase, an essential regulator of mitosis. BRD4 binding to Aurora B inhibits its kinase activity, preventing autophosphorylation and phosphorylation of the key mitotic targets histone H3 and MCAK, the mitotic centromere associated kinesin. This inhibition is relieved during metaphase when JNK is activated and phosphorylates BRD4, triggering its transient release from chromatin. Importantly, Aurora B activity during mitosis inversely correlates with BRD4 binding and directly correlates with JNK activation and BRD4 release. Our findings thus reveal a regulatory mechanism whereby Aurora B activity is directly controlled by BRD4, which in turn is regulated by JNK.
Significance Statement: BRD4 has been extensively characterized for its role in regulating chromatin structure and transcription. But its function during mitosis has remained unclear. This study reveals a novel mechanism by which BRD4 directly regulates mitotic progression through its interaction with and inhibition of Aurora B kinase, a central player in chromosome segregation. The timely release of BRD4 from chromatin via JNK-mediated phosphorylation enables Aurora B activation at a critical stage of mitosis. These findings uncover a previously unrecognized BRD4-Aurora B-JNK signaling axis that integrates chromatin dynamics with mitotic control, offering new insights into cell cycle regulation and potential therapeutic targets in cancer.

DOI: https://doi.org/10.1101/2025.08.06.668960
Mol Plant Pathol. 2025 Sep;26(9): e70157

MoMad2 With a Conserved Function in the Spindle Assembly Checkpoint Is Required for Maintaining Appressorial Turgor Pressure and Pathogenicity of Rice Blast Fungus.

Tianjiao Shen, Qiushi Chen, Ioanna Leontiou, Rong Wang, Meiling Su, Qiong Luo, Guodong Lu, Zonghua Wang, Ya Li, Kevin G Hardwick, Mo Wang.

  Mad2, a conserved core component of the spindle assembly checkpoint (SAC) in eukaryotes, delays anaphase onset in case of incorrect kinetochore-microtubule attachment. However, its functions in plant-pathogenic fungi remain largely unknown. Here, we identified the Mad2 homologue in rice blast fungus Magnaporthe oryzae (MoMad2), which shows high similarity with Mad2 in fission yeast. When expressed in fission yeast, MoMad2 associated with native SpMad1 and SpCdc20, and successfully rescued the ΔSpmad2 mutant's defect in arresting anaphase onset upon damaged spindle, indicating the conserved SAC function of MoMad2. Moreover, MoMad2 interacted with MoMad1 and depends on MoMad1 for its nuclear envelope-localisation. Although it plays a dispensable role in M. oryzae growth, MoMad2 is required for tolerance to the microtubule depolymerising agent treatment. ΔMomad2 mutants exhibited shorter hyphal compartments and earlier conidial germination and appressorium formation, suggesting that MoMad2 deletion shortens M. oryzae's mitotic cell cycle due to defective SAC arrest. Additionally, knockout of MoMAD2 decreased the appressorial turgor pressure, impaired appressorium penetration and compromised M. oryzae pathogenicity. Taken together, our findings revealed that MoMad2, as a conserved component in SAC signalling, is essential for full pathogenicity of rice blast fungus.

Keywords:   Magnaporthe oryzae ; Mad2; appressorial turgor; pathogenicity; spindle assembly checkpoint

DOI:  https://doi.org/10.1111/mpp.70157
bioRxiv. 2025 Sep 02. pii: 2025.09.02.673761. [Epub ahead of print]

A minimum module for positioning the Chromosomal Passenger Complex at the cell center for cytokinesis.

Konstantinos Nakos, Sithara Wijeratne, Michael Blower, Radhika Subramanian.

The Aurora B kinase-containing Chromosomal Passenger Complex (CPC) is an essential regulator of cytokinesis, the final and irreversible step of cell division. During anaphase, the CPC concentrates at the spindle midzone - a bundle of overlapping antiparallel microtubules organized at the cell center. How CPC is selectively enriched at the midzone within the dense, heterogeneous, and dynamic spindle microtubule network is unknown. Here, we define a minimal CPC midzone enrichment module. We show that the maximal enrichment of CPC at antiparallel microtubule overlaps requires PRC1-crosslinked microtubules and the interaction of CPC with two mitotic kinesins, KIF4A and KIF20A. We find that the two motors exhibit a division of labor: KIF20A delivers CPC from non-overlapping microtubules, and KIF4A retains CPC at PRC1-crosslinked overlaps. Conditional depletion of KIF4A in mitotic cells reveals that it is required for CPC localization at the spindle midzone in anaphase. Taken together, our findings reveal how the collective activity of two kinesins enables navigation through the complex microtubule network of the spindle to organize kinase signaling at the cell center for cytokinesis.

DOI: https://doi.org/10.1101/2025.09.02.673761
Open Biol. 2025 Sep;15(9): 250199

A distinct phase of cyclin B (Cdc13) nuclear export at mitotic entry in Schizosaccharomyces pombe.

Samir G Chethan, Jessie M Rogers, Drisya Vijayakumari, Wendi Williams, Vojislav Gligorovski, Sahand Jamal Rahi, Silke Hauf.

  In eukaryotes, cell division requires coordination between the nucleus and cytoplasm. Entry into cell division is driven by cyclin-dependent kinases (CDKs), which need a cyclin binding partner for their activity. In Schizosaccharomyces pombe (fission yeast), the B-type cyclin Cdc13 is essential and sufficient for cell cycle progression and is strongly enriched in the nucleus. Here, we show that a fraction of Cdc13 is exported from the nucleus to the cytoplasm just prior to mitosis. This export could be critical to propagate CDK activity throughout the cell. Mutating three Cdc13 nuclear localization signals (NLSs) led to precocious enrichment of Cdc13 in the cytoplasm but did not accelerate mitotic entry, indicating that the export is not sufficient to trigger entry into mitosis. The export coincides with spindle pole body integration into the nuclear envelope and may be required to coordinate nuclear and cytoplasmic signalling required for this integration. The onset and stop of Cdc13 nuclear export are remarkably abrupt, underscoring that S. pombe mitotic entry consists of several switch-like transitions over the course of minutes. Our findings add another instance to the various cyclin nuclear transport events known to occur at critical cell cycle transitions throughout eukaryotes.

Keywords:  Schizosaccharomyces pombe; cell cycle; cyclin B; mitotic entry; nucleocytoplasmic transport

DOI:  https://doi.org/10.1098/rsob.250199
Mol Biol Cell. 2025 Sep 17. mbcE25050214

Robust CENP-A incorporation in human cells is independent of transcription and cohesin components.

Reito Watanabe, Carlos Perea-Resa, Michael D Blower.

Centromeres are essential chromosomal components that ensure proper cell division by serving as assembly sites for kinetochores, which connect chromosomes to spindle microtubules. Centromeres are marked by the evolutionarily conserved centromere-specific histone H3 variant, CENP-A, which is deposited into centromere nucleosomes during G1 in human cells. Centromeres retain cohesin, a ring-like protein complex during mitosis, protecting sister chromatid cohesion and centromere transcription to prevent chromosome missegregation. Previous work in Drosophila has suggested that centromere transcription and centromeric RNAs are important for CENP-A deposition in chromatin. During mitosis centromeric cohesin is critical for centromere transcription. However, it is not clear how or if centromeric transcription and cohesin contribute to CENP-A deposition in G1 in human cells. To address these questions, we combined a cell synchronization strategy with the Auxin Inducible Degron technology and transcription inhibition in human cells. In contrast to Drosophila cells, our results demonstrated that neither centromeric transcription nor cohesin is required for CENP-A deposition in human cells. Our data demonstrate clear differences in the CENP-A deposition mechanism between human and Drosophila cells. These findings provide deeper insights into the plasticity underlying centromere maintenance and highlight evolutionary divergence in centromere maintenance systems across species.

DOI: https://doi.org/10.1091/mbc.E25-05-0214
Curr Biol. 2025 Sep 12. pii: S0960-9822(25)01105-4. [Epub ahead of print]

The conserved machinery of bipolar prospindle formation controls acentrosomal spindle orientation in land plants.

Takema Sasaki, Kimitsune Ishizaki, Hiroyasu Motose, Yoshihisa Oda.

  Correct spindle orientation is essential for the development of multicellular organisms.1,2 In animal cells, astral microtubules control spindle orientation by determining the position of centrosomes.1 However, the mechanisms that determine spindle orientation in acentrosomal plant cells are poorly understood. Here, we show that the microtubule-associated protein CORD3,4 controls spindle orientation via prospindle assembly in the liverwort Marchantia polymorpha (Marchantia) and the angiosperm Arabidopsis thaliana (Arabidopsis). Wild-type cells formed bipolar microtubule structures called prospindles prior to nuclear envelope breakdown and assembled spindles along the prospindle axis. By contrast, CORD-deficient cells failed to maintain the bipolar prospindle, leading to the formation of multipolar prospindles and spindle misorientation. Spindle misorientation also caused phragmoplast misorientation, leading to abnormal cell plate alignment, although phragmoplast orientation was partially corrected during telophase. These results suggest that CORD maintains prospindle bipolarity, thereby controlling proper spindle orientation in Marchantia and Arabidopsis. This study reveals a conserved mechanism for the control of acentrosomal spindle orientation in land plants.

Keywords:  Arabidopsis; CORD; Marchantia; acentrosomal mitosis; microtubule; prospindle; spindle orientation

DOI:  https://doi.org/10.1016/j.cub.2025.08.038
bioRxiv. 2025 Sep 08. pii: 2025.09.08.674938. [Epub ahead of print]

The dynamics of centromere assembly and disassembly during quiescence.

Océane Marescal, Kuan-Chung Su, Brittania Moodie, Noah J L Taylor, Iain M Cheeseman.

Quiescence is a state in which cells undergo a prolonged proliferative arrest while maintaining their capacity to reenter the cell cycle. Here, we analyze entry and exit from quiescence, focusing on how cells regulate the centromere, a structure involved in chromosome segregation. Despite the constitutive localization of centromere proteins throughout the cell cycle, we find that cells rapidly disassemble most centromere proteins during quiescence entry, while preserving those required to maintain centromere identity. During quiescence exit, the centromere is reassembled and rapidly regains normal homeostatic levels of centromere proteins. Although the histone variant CENP-A is typically deposited during G1, we find that CENP-A deposition does not occur during the G1 immediately following quiescence exit, and instead occurs after cells complete their first mitosis. In contrast, other centromere proteins relocalize during the first S phase independent of DNA replication. These findings reveal centromere dynamics during quiescence entry and exit and highlight paradigms for the timing and control of centromere protein deposition.

DOI: https://doi.org/10.1101/2025.09.08.674938
Nat Commun. 2025 Sep 19. 16(1): 8323

Spindle-localized F-actin regulates polar MTOC organization and the fidelity of meiotic spindle formation.

Edgar J Soto-Moreno, Nourhan N Ali, Florian Küllmer, Veselin Nasufovic, Michaela Frolikova, Olga Tepla, Jaromir Masata, Dirk Trauner, Amanda A Patterson, Hans-Dieter Arndt, Katerina Komrskova, Magdalena Zernicka-Goetz, David M Glover, Ahmed Z Balboula.

Mammalian oocytes are notoriously prone to chromosome segregation errors leading to aneuploidy. The spindle provides the machinery for accurate chromosome segregation during cell division. Mammalian oocytes lack centrioles and, therefore, mouse meiotic spindle relies on the organization of numerous acentriolar microtubule organizing centers into two poles (polar microtubule organizing centers, pMTOCs). The traditional view is that, in mammalian oocytes, microtubules are the sole cytoskeletal component responsible for regulating pMTOC organization and spindle assembly. We identify a previously unrecognized F-actin pool that surrounds pMTOCs, forming F-actin cage-like structure. We demonstrate that F-actin localization on the spindle depends on unconventional myosins X and VIIb. Selective disruption of spindle-localized F-actin, using myosin X/VIIb knockdown oocytes or photoswitchable Optojasp-1, perturbs pMTOC organization, leading to unfocused spindle poles and chromosome missegregation. Here, we unveil an important function of spindle-localized F-actin in regulating pMTOC organization, a critical process for ensuring the fidelity of meiotic spindle formation and proper chromosome segregation.

DOI: https://doi.org/10.1038/s41467-025-63586-w
bioRxiv. 2025 Sep 02. pii: 2025.09.01.673455. [Epub ahead of print]

An electrostatic repulsion model of centromere organisation.

Caelan Bell, Lifeng Chen, M Julia Maristany, Claudia Blaukopf, Huabin Zhou, Jan Huertas, Jose I Perez Lopez, Christoph C H Langer, Thomas L Steinacker, Nikki Schuette, Lynda Doolittle, Jorge R Espinosa, Sy Redding, Rosana Collepardo-Guevara, Michael K Rosen, Daniel W Gerlich.

During cell division, chromosomes reorganise into compact bodies in which centromeres localise precisely at the chromatin surface to enable kinetochore-microtubule interactions essential for genome segregation. The physical principles guiding this centromere positioning remain unknown. Here, we reveal that human core centromeres are directed to the chromatin surface by repulsion of centromere-associated proteins - independent of condensin-mediated loop extrusion and microtubule engagement. Using cellular perturbations, biochemical reconstitution, and multiscale molecular dynamics simulations, we show that chromatin surface localisation emerges from repulsion between condensed chromatin and both the kinetochore and the highly negatively charged centromere protein, CENP-B. Together, these elements form a centromeric region composed of two domains with opposing affinities, one favouring integration within the mitotic chromosome and the other favouring exposure to the surrounding cytoplasm, thereby driving surface positioning. Tethering synthetic negatively charged proteins to chromatin was sufficient to recapitulate this surface localisation in cells and in vitro, indicating that electrostatic repulsion is a key determinant of surface localisation. These findings demonstrate that centromere layering is not hardwired by chromatin folding patterns but instead emerges from phase separation in chromatin. Our work uncovers electrostatic polarity as a general and programmable mechanism to spatially organise chromatin.

DOI: https://doi.org/10.1101/2025.09.01.673455
Biophys J. 2025 Sep 18. pii: S0006-3495(25)00601-0. [Epub ahead of print]

Chromatin Compaction Scaling with Cell Size Follows a Power Law from Interphase Through Mitosis.

Petra Stockinger, Anna Oddone, Melike Lakadamyali, Manuel Mendoza, Jérôme Solon.

Coordination of mitotic chromosome compaction with cell size is crucial for proper genome segregation during mitosis. During development, DNA content remains constant but cell size changes dynamically, necessitating a mechanism that scales chromosome compaction with cell size to ensure proper chromatin segregation. In this study, we examined chromatin compaction in the developing Drosophila nervous system by analyzing the large neuronal stem cells and their smaller progeny, the ganglion mother cells. Using super-resolution 3D Stochastic Optical Reconstruction Microscopy and quantitative time-lapse fluorescence microscopy, we observed that nanoscale chromatin density during interphase scales with nuclear volume according to a power law. This scaling relationship is disrupted by inhibiting histone deacetylase activity, indicating that molecular cues rather than mechanical constraints primarily regulate chromatin compaction. Notably, this power law dependency is maintained into mitosis but the scaling exponent decreases. This suggests a phase separation-like transition in the biophysical state of chromatin, whereby the polymer shifts from a more expanded to a more compact configuration. Accordingly, we propose that the scaling of mitotic chromosome size relative to cell size emerges from the organisational principles of interphase chromatin, and that mitotic compaction may be governed by polymer properties modulated by changes in the chromatin - solvent environment.

DOI: https://doi.org/10.1016/j.bpj.2025.09.021
Mol Biol Cell. 2025 Sep 17. mbcE25080375

The spatial arrangement of chromosomes determines fusion of nucleoli in diploid budding yeast.

Philipp Girke, Simone Fabian, Leonie Aberle, Wolfgang Seufert.

The nucleolus is a non-membrane-bound compartment that forms around tandem arrays of ribosomal RNA genes (rDNA) and provides the cell with ribosomes. Multiple nucleoli within the same nucleus coalesce, and fusion is thought to result mainly from intrinsic properties of nucleoli. However, rDNA arrays are mostly in chromosomal context, and chromosomes are not randomly organized. How the spatial arrangement of chromosomes affects nucleolar fusion is largely unknown. Using fluorescence microscopy, we investigated nucleolar fusion in diploid budding yeast. Nucleoli forming around homologous rDNA arrays efficiently fused during interphase but often individualized during late anaphase. While nucleoli were far from the spindle pole body (SPB) in interphase, they came close during mitosis suggesting that SPB-dependent positioning may affect nucleolar fusion. Indeed, disruption of microtubule-dependent centromere anchorage to the SPB by nocodazole promoted individualization of nucleoli. In contrast, impairment of rDNA tethering to the nuclear envelope had little or no effect. Hence, chromosome positioning by non-rDNA sequences facilitates nucleolar fusion.

DOI: https://doi.org/10.1091/mbc.E25-08-0375
MicroPubl Biol. 2025 ;2025

The embryonic lethal mutation zyg-10(b261) is an allele of the atx-2 gene and disrupts multiple aspects of early embryogenesis.

Zachary G Bell, Harold E Smith, Kevin F O'Connell.

The zyg-10 ( b261 ) mutation was identified in one of the earliest screens for temperature-sensitive embryonic lethal mutations in C. elegans , but the cytological defects underlying the embryonic lethal phenotype, as well as the molecular identity of zyg-10 had not been previously established. Here we show that zyg-10 ( b261 ) is an allele of the atx-2 (ataxin-related) gene and that embryos produced by atx-2 ( b261 ) mothers exhibit a variety of defects including eggshell defects, cytokinesis failure, spindle mispositioning, and chromosome missegregation. We also show that the localization of separase, a regulator of egg-shell formation and mitosis, is defective in atx-2 ( b261 ) embryos.

DOI: https://doi.org/10.17912/micropub.biology.001714
bioRxiv. 2025 Sep 04. pii: 2025.09.04.674221. [Epub ahead of print]

Cellular mechanism linking endoplasmic reticulum inheritance and cell cycle regulation of the nuclear genome.

Ya-Shiuan Lai, Jesse Chao, Maho Niwa.

Endoplasmic reticulum (ER) stress triggers activation of the ER surveillance (ERSU) pathway- a critical protective mechanism that transiently halts cortical ER inheritance to daughter cells and arrests cytokinesis by septin ring subunit Shs1 re-localization to the bud scar in response to ER stress. Once ER functional homeostasis is re-established, cells resume normal cell cycle progression; however, the molecular circuitry linking ER integrity to cell cycle regulation has remained largely unresolved. Here, we show that ER stress selectively disperse Bud2, a GAP for Bud1/Rsr1, severing its canonical role in cell polarity while integrating it into ER homeostasis signaling. Bud2 dispersion results in accelerated spindle pole body (SPB) duplication, spindle misorientation, defects in nuclear migration, and genome segregation errors under ER stress. Strikingly, a C-terminal truncation of Shs1 ( shs1-ΔCTD ) recapitulated the ER stress-induced dispersion of Bud2 phenotype even in the absence of ER stress, and delayed cell-cycle re-entry after ER homeostasis was regained-despite normal occurrence of typical ERSU hallmark events. Notably, Bud2 overexpression rescued the growth defects of shs1-ΔCTD mutants after ER homeostasis was re-established. Collectively, our findings reveal a new mechanistic axis whereby ER integrity coordinates organelle inheritance, cytoskeletal organization, and nuclear division via selective control of Bud2 and Shs1, establishing a direct regulatory bridge between ER status and mitotic fidelity.

DOI: https://doi.org/10.1101/2025.09.04.674221
bioRxiv. 2025 Sep 08. pii: 2025.09.08.674396. [Epub ahead of print]

Hydrophobic interactions of FG-nucleoporins are required for dilating nuclear membrane pores into selective transport channels after mitosis.

Wanlu Zhang, Andrew P Latham, Paolo Ronchi, Sebastian Schnorrenberg, Jean-Karim Hériché, Ziqiang Huang, M Julius Hossain, Natalia Rosalia Morero, Hannah Pflaumer, Merle Hantsche-Grininger, Yannick Schwab, Andrej Sali, Jan Ellenberg.

Nuclear envelope (NE) reformation after mitosis is essential for daughter cell viability and requires tightly coordinated nuclear pore complex (NPC) assembly and nuclear membrane reformation. To reveal how these processes are mechanistically linked, we combined acute molecule perturbations in live cells with correlative 3D electron tomography or MINFLUX super-resolution microscopy. We show that degrading Nup62 during mitosis arrests NPC assembly at an intermediate step with smaller membrane pores and removes the whole central transport channel. Molecular dynamics simulations predicted that 32 copies of the central channel subcomplex, recruited into the previously unoccupied pore center, can self-associate via hydrophobic interactions to occupy the volume required for full pore size and exert an outward pushing force; indeed, disrupting these interactions during NPC assembly blocked pore dilation. Later in mitotic exit, perturbed cells exhibited impaired nuclear import, smaller nuclei, and looser NE spacing. Acute inhibition of nuclear import recapitulated these NE defects without affecting NPC assembly. Together, our findings reveal a new, two-step molecular mechanism linking NPC assembly and NE reformation. First, hydrophobic FG-nucleoporins dilate the assembling nuclear pore to its full width by forming the central transport channel, which then allows nuclear import-driven nuclear expansion leading to tight, regular NE membrane spacing.

DOI: https://doi.org/10.1101/2025.09.08.674396
Adv Sci (Weinh). 2025 Sep 15. e11682

Polo-Like Kinase 1 Phosphorylation Tunes the Functional Viscoelastic Properties of the Centrosome Scaffold.

Matthew Amato, June Ho Hwang, Manolo U Rios, Nicole E Familiari, Michael K Rosen, Jeffrey B Woodruff.

  Cytoskeleton-organizing organelles often function while under mechanical load. The outer layer of centrosomes, called pericentriolar material (PCM), nucleates microtubules that move chromosomes during mitosis. How PCM resists microtubule-mediated forces is poorly understood at the material level. This study shows that PLK-1 phosphorylation of SPD-5 tunes the dynamics and material properties of the PCM scaffold in C. elegans embryos. Microrheology of reconstituted SPD-5 scaffolds reveals that PLK-1 phosphorylation decreases SPD-5 dynamics and increases scaffold viscoelasticity. Similarly, in embryos, phospho-mimetic SPD-5 is less dynamic than wild-type SPD-5, which itself is less dynamic than phospho-null SPD-5. PCM built with phospho-null SPD-5 is smaller than normal, but its assembly can be partially rescued by reducing microtubule-dependent forces. The same is true for PCM built with phospho-mimetic SPD-5, yet the underlying causes are distinct: under force, phospho-null SPD-5 fails to assemble, while phospho-mimetic SPD-5 forms hyper-stable foci that fail to cohere into a uniform, spherical mass. Both mutants have defects with chromosome segregation and viability. Thus, tuning of SPD-5 phosphorylation optimizes PCM material properties to achieve correct PCM size, integrity, and function. These results demonstrate how regulated chemical modification of a scaffolding protein tunes the material properties and function of a microtubule-organizing organelle.

Keywords:  PLK‐1; SPD‐5; TPXL‐1; centrosome; condensate; pericentriolar material; scaffold

DOI:  https://doi.org/10.1002/advs.202511682
Chromosome Res. 2025 Sep 16. 33(1): 20

CENP-A is diluted during bovine spermatogenesis and is maintained at internally positioned centromere clusters in mature bull sperm.

Miriama Štiavnická, Anna Ní Nualláin, Caitríona M Collins, Elaine M Dunleavy.

  During spermatogenesis, chromatin structure is remodelled by the incorporation of distinct histone variants and associated posttranslational modifications, followed by the almost complete replacement of histones by protamines in sperm. However, the dynamics of the centromere-specific histone H3 variant CENP-A have not yet been elucidated during spermatogenesis in mammals. Here we investigate CENP-A localisation dynamics in cattle (Bos taurus). In bovine testis tissue sections, we quantify CENP-A intensity in key germ cell types; spermatogonia (pre-meiotic), primary spermatocytes (meiotic) and spermatids (post-meiotic). Our quantitation shows that spermatogonia harbour the highest amount of CENP-A compared to all other germ cell types. Spermatids have approximately one quarter the amount of CENP-A of spermatogonia indicating that overall, it is reduced and maintained through the two meiotic divisions. Yet, we also observed some unexpected dynamics. CENP-A is asymmetrically distributed such that undifferentiated spermatogonia harbour more CENP-A that differentiated spermatogonia that enter meiosis. We also noted an increase in CENP-A intensity in primary spermatocytes during meiotic prophase I, which is indicative of centromere assembly at this time. We also confirm the specific maintenance of CENP-A, and the absence of the centromeric DNA binding protein CENP-B, on mature bull sperm nuclei that have completed histone-to-protamine exchange. Finally, we present a model for centromere positioning in mature sperm nuclei and propose that centralised clustering of centromeres may serve a protective function during histone-to-protamine exchange.

Keywords:  Bull sperm; CENP-A; Centromeres; Meiosis; Spermatogonia stem cells

DOI:  https://doi.org/10.1007/s10577-025-09781-3
J Cell Sci. 2025 Sep 17. pii: jcs.263622. [Epub ahead of print]

MLL/WDR5 complex promotes recruitment of KIF2C to midbody to ensure MT depolymerization and furrow initiation during cytokinesis.

Avishek Kataria, Neeraja Hemalatha, Akash Chinchole, Shweta Tyagi.

  Mixed-lineage leukemia (MLL) protein is a well-characterised epigenetic regulator whose non-canonical activities remain underappreciated. MLL has been shown to localize on the midbody and loss of this protein leads to binucleation. However, the critical role of the MLL complex in midbody formation remains underexplored. Here, we further characterize the localization of MLL and its associated protein WDR5 to the midbody. Loss of MLL/WDR5 results in defective midbody formation, which displays a wide midzone-like microtubule structure, along with chromosome bridges, resulting in binucleated cells. We show that MLL and WDR5 interact with kinesin 13 motor-KIF2C, and target it to the midbody. The depolymerase activity of KIF2C promotes correct localization of centralspindlin complex, compaction of midzone MTs, and finally, timely furrow initiation. Thus, we identify a previously unrecognized role for MLL and KIF2C in cytokinesis regulation. Together with earlier findings, this implicates them in the regulation of actin-microtubule cytoskeleton interface-pathways frequently altered in oncogenesis.

Keywords:  Binucleation; Furrow initiation; KIF2C; MLL; MT depolymerase; Midbody

DOI:  https://doi.org/10.1242/jcs.263622
J Pathol. 2025 Sep 15.

Chromosomal instability and genomic alterations in cholangiocarcinoma from Northeastern Thailand.

Raksawan Deenonpoe, Molly A Guscott, Sasithorn Watcharadetwittaya, Isabel L McNeill, Daniela Moralli, Nadeem Shaikh, Sarah E McClelland.

  Cholangiocarcinoma (CCA) is a lethal cancer of the bile duct and is a major health concern in several parts of the world, including northeastern Thailand, where CCA incidence is the highest due to the endemic liver fluke Opisthorchis viverrini. Multiple studies have characterised genomic alterations in CCA tumours, and specific chromosomal alterations can predict prognosis. However, it is not known whether chromosomal instability (CIN), ongoing genomic alteration characteristic of most cancer types, is present in CCA tumours. In this study we leveraged a panel of cancer cell lines derived from fluke-positive CCA patients, as well as a matched normal cholangiocyte line as a control, to characterise CIN in CCA. We observed elevated rates of chromosome segregation errors compared to normal cells, although overall CIN rates were lower than those for highly genomically unstable cancers, such as colorectal or ovarian cancer. Chromosome segregation errors in CCA cell lines were potentially driven by elevated DNA replication stress and centrosome duplication. Single-cell genome sequencing and karyotyping of the cell lines showed extensive structural and numerical chromosomal aberrations, as well as copy number alterations that were heterogeneous between individual cells, supporting the presence of ongoing CIN in these cell line models. Low-pass whole-genome sequencing of 33 CCA tumour samples with matched normal tissue from northeastern Thailand, a liver fluke-endemic region showed increased whole and subchromosomal level alterations, with a higher extent of genomic alterations in intrahepatic tumours compared to extrahepatic. Eight tumours carried focal amplifications and/or deletions involving known cancer genes, as well as potential chromosomal instability-associated genes, including CCNE1 amplifications and a rare amplification of BRCA1. This study provides increased understanding of the rate and potential mechanisms of CIN in CCA that may inform new therapeutic strategies that synergise with specific ongoing CIN mechanisms. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Keywords:  Northern Thailand.; cholangiocarcinoma; chromosomal instability; copy number alterations; heterogeneity; liver fluke; single‐cell sequencing

DOI:  https://doi.org/10.1002/path.6464
Leukemia. 2025 Sep 15.

CRISPR-engineered human GATA2 deficiency model uncovers mitotic dysfunction and premature aging in HSPCs, impairing hematopoietic fitness.

Damia Romero-Moya, Eric Torralba-Sales, Cristina Calvo, Oskar Marin-Bejar, Maria Magallon-Mosella, Maximiliano Distefano, Joan Pera, Julio Castaño, Francesca De Giorgio, Jessica Gonzalez, Arnau Iglesias, Clara Berenguer-Balaguer, Marcel Schilling, Mireya Plass, Lorenzo Pasquali, Albert Català, Oscar Molina, Marcin W Wlodarski, Anna Bigas, Alessandra Giorgetti.

GATA2 deficiency is a monogenic transcriptopathy disorder characterized by bone marrow failure (BMF), immunodeficiency, and a high risk of developing myelodysplastic neoplasms (MDS) and acute myeloid leukemia (AML). Although informative mouse models have been developed, the mechanisms by which GATA2 haploinsufficiency drives disease initiation in humans remain incompletely understood. To address this, we developed a novel humanized model using CRISPR/Cas9 technology to knock-in GATA2-R398W variant in primary cord blood CD34⁺ cells. Additionally, we introduced specific mutations in SETBP1 and ASXL1 to model distinct premalignant stages of GATA2 deficiency. Through clonal competition and serial transplantation assays, we demonstrated that human CD34+ cells harboring the GATA2 mutation exhibit significantly reduced fitness in vivo when compete with wild-type cells. Notably, this fitness disadvantage persists even when GATA2 mutations are combined with oncogenic SETBP1 and ASXL1 drivers, underscoring the dominant, deleterious effect of GATA2 deficiency on hematopoietic stem cell function. Functional in vitro analyses revealed that GATA2-R398W mutation impairs cell proliferation, disrupts cell cycle progression, and induces mitotic defects, which may contribute to hematopoietic stem/progenitor cell loss and impaired self-renewal. Transcriptomic profiles of GATA2-mutant cells revealed that these functional defects are associated with reduced HSC self-renewal capacity and upregulation of the pre-aging phenotype. Our work highlights the feasibility of generating a human GATA2 deficiency model suitable for studying the biological consequences of various GATA2 variants and the generation of a platform to test potential phenotype-rescuing therapeutics.

DOI: https://doi.org/10.1038/s41375-025-02771-8