bims-micesi 2025-01-12 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2025–01–12
six papers selected by
Valentina Piano, Uniklinik Köln

CAMSAP2 is required for bridging fiber assembly to ensure mitotic spindle assembly and chromosome segregation in human epithelial Caco-2 cells.
Independence of Centromeric and Pericentromeric Chromatin Stability on CCAN Components.
Mechanisms, Machinery, and Dynamics of Chromosome Segregation in Zea mays.
Cell shape modulates mitotic spindle positioning forces via intracellular hydrodynamics.
MDM2 functions as a timer reporting the length of mitosis.
Chromosome mis-segregation triggers cell cycle arrest through a mechanosensitive nuclear envelope checkpoint.

PLoS One. 2025 ;20(1): e0308150

CAMSAP2 is required for bridging fiber assembly to ensure mitotic spindle assembly and chromosome segregation in human epithelial Caco-2 cells.

Naoko Nishizawa, Riku Arai, Koki Hiranuma, Mika Toya, Masamitsu Sato.

In mammalian epithelial cells, cytoplasmic microtubules are mainly non-centrosomal, through the functions of the minus-end binding proteins CAMSAP2 and CAMSAP3. When cells enter mitosis, cytoplasmic microtubules are reorganized into the spindle composed of both centrosomal and non-centrosomal microtubules. The function of the CAMSAP proteins upon spindle assembly remains unknown, as these do not exhibit evident localization to spindle microtubules. Here, we demonstrate that CAMSAP2, but not CAMSAP3, is required for spindle assembly upon mitotic entry. CAMSAP2 knockout (KO) Caco-2 cells showed a delay in mitotic progression, whereas CAMSAP3 KO cells did not. The spindle in CAMSAP2 KO cells was short and displayed a reduced microtubule density, particularly around chromosomes. This indicated a loss of bridging fibers, which are known to assist alignment of sister kinetochores through interaction with kinetochore fibers. Consistent with this, live-cell imaging of CAMSAP2 KO cells captured slow elongation of the anaphase spindle and errors in chromosome segregation. Therefore, we propose that CAMSAP2 ensures efficient reorganization of cytoplasmic microtubules into the mitotic spindle through constructing bridging fibers that assist faithful segregation of sister chromatids.

DOI: https://doi.org/10.1371/journal.pone.0308150
bioRxiv. 2024 Dec 19. pii: 2024.12.18.628896. [Epub ahead of print]

Independence of Centromeric and Pericentromeric Chromatin Stability on CCAN Components.

Ronald J Biggs, Kousik Sundararajan, Mingxuan Sun, Eline Hendrix, Aaron F Straight, John F Marko.

The chromatin of the centromere provides the assembly site for the mitotic kinetochore that couples microtubule attachment and force production to chromosome movement in mitosis. The chromatin of the centromere is specified by nucleosomes containing the histone H3 variant CENP-A. The constitutive centromeric-associated network (CCAN) and kinetochore are assembled on CENP-A chromatin to enable chromosome separation. CENP-A chromatin is surrounded by pericentromeric heterochromatin and bound by the sequence specific binding protein CENP-B. We performed mechanical experiments on mitotic chromosomes while tracking CENP-A and CENP-B to observe the centromere's stiffness and the role of the CCAN. We degraded CENP-C and CENP-N using auxin-inducible degrons, which we verified compromises the CCAN via observation of CENP-T loss. Chromosome stretching revealed that the CENP-A domain does not visibly stretch, even in the absence of CENP-C and/or CENP-N. Pericentromeric chromatin deforms upon force application, stretching approximately 3-fold less than the entire chromosome. CENP-C and/or CENP-N loss has no impact on pericentromere stretching. Chromosome-disconnecting nuclease treatments showed no structural effects on CENP-A. Our experiments show that the core-centromeric chromatin is more resilient and likely mechanically disconnected from the underlying pericentromeric chromatin, while the pericentric chromatin is deformable yet stiffer than the chromosome arms.

DOI: https://doi.org/10.1101/2024.12.18.628896
Genes (Basel). 2024 Dec 16. pii: 1606. [Epub ahead of print]15(12):

Mechanisms, Machinery, and Dynamics of Chromosome Segregation in Zea mays.

Marissa E Duffy, Michael Ngaw, Shayna E Polsky, Abby E Marzec, Sean S Zhang, Owen R Dzierzgowski, Natalie J Nannas.

  Zea mays (maize) is both an agronomically important crop and a powerful genetic model system with an extensive molecular toolkit and genomic resources. With these tools, maize is an optimal system for cytogenetic study, particularly in the investigation of chromosome segregation. Here, we review the advances made in maize chromosome segregation, specifically in the regulation and dynamic assembly of the mitotic and meiotic spindle, the inheritance and mechanisms of the abnormal chromosome variant Ab10, the regulation of chromosome-spindle interactions via the spindle assembly checkpoint, and the function of kinetochore proteins that bridge chromosomes and spindles. In this review, we discuss these processes in a species-specific context including features that are both conserved and unique to Z. mays. Additionally, we highlight new protein structure prediction tools and make use of these tools to identify several novel kinetochore and spindle assembly checkpoint proteins in Z. mays.

Keywords:  Zea mays; chromosome; kinetochore; meiosis; meiotic drive; mitosis; spindle; spindle assembly checkpoint

DOI:  https://doi.org/10.3390/genes15121606
Curr Biol. 2024 Dec 28. pii: S0960-9822(24)01622-1. [Epub ahead of print]

Cell shape modulates mitotic spindle positioning forces via intracellular hydrodynamics.

Jing Xie, Javad Najafi, Aude Nommick, Luc Lederer, Jeremy Salle, Serge Dmitrieff, Benjamin Lacroix, Julien Dumont, Nicolas Minc.

  The regulation of mitotic spindle positioning and orientation is central to the morphogenesis of developing embryos and tissues.1,2,3,4,5 In many multicellular contexts, cell geometry has been shown to have a major influence on spindle positioning, with spindles that commonly align along the longest cell shape axis.6,7,8,9,10,11,12,13,14 To date, however, we still lack an understanding of how the nature and amplitude of intracellular forces that position, orient, or hold mitotic spindles depend on cell geometry. Here, we used in vivo magnetic tweezers to directly measure the forces that maintain the mitotic spindle in the center of sea urchin cells that adopt different shapes during early embryo development. We found that spindles are held by viscoelastic forces that progressively increase in amplitude as cells become more elongated during early development. By coupling direct cell shape manipulations in microfabricated chambers with in vivo force measurements, we establish how spindle-associated forces increase in dose dependence with cell shape anisotropy. Cytoplasm flow analysis and hydrodynamic simulations suggest that this geometry-dependent mechanical enhancement results from a stronger hydrodynamic coupling between the spindle and cell boundaries, which dampens cytoplasm flows and spindle mobility as cells become more elongated. These findings establish how cell shape affects spindle-associated forces and suggest a novel mechanism for shape sensing and division positioning mediated by intracellular hydrodynamics with functional implications for early embryo morphogenesis.

Keywords:  cell division; cell shape; cytoplasm; embryogenesis; flows; forces; mitotic spindles

DOI:  https://doi.org/10.1016/j.cub.2024.11.055
Nat Cell Biol. 2025 Jan 09.

MDM2 functions as a timer reporting the length of mitosis.

Luke J Fulcher, Tomoaki Sobajima, Caleb Batley, Ian Gibbs-Seymour, Francis A Barr.

Delays in mitosis trigger p53-dependent arrest in G1 of the next cell cycle, thus preventing repeated cycles of chromosome instability and aneuploidy. Here we show that MDM2, the p53 ubiquitin ligase, is a key component of the timer mechanism triggering G1 arrest in response to prolonged mitosis. This timer function arises due to the attenuation of protein synthesis in mitosis. Because MDM2 has a short half-life and ongoing protein synthesis is therefore necessary to maintain its steady-state concentration, the amount of MDM2 gradually falls during mitosis but normally remains above a critical threshold for p53 regulation at the onset of G1. When mitosis is extended by prolonged spindle assembly checkpoint activation, the amount of MDM2 drops below this threshold, stabilizing p53. Subsequent p53-dependent p21 accumulation then channels G1 cells into a sustained cell-cycle arrest, whereas abrogation of the response in p53-deficient cells allows them to bypass this crucial defence mechanism.

DOI: https://doi.org/10.1038/s41556-024-01592-8
Nat Cell Biol. 2025 Jan 08.

Chromosome mis-segregation triggers cell cycle arrest through a mechanosensitive nuclear envelope checkpoint.

Solène Hervé, Andrea Scelfo, Gabriele Bersano Marchisio, Marine Grison, Kotryna Vaidžiulytė, Marie Dumont, Annapaola Angrisani, Adib Keikhosravi, Gianluca Pegoraro, Mathieu Deygas, Guilherme P F Nader, Anne-Sophie Macé, Matteo Gentili, Alice Williart, Nicolas Manel, Matthieu Piel, Yekaterina A Miroshnikova, Daniele Fachinetti.

Errors during cell division lead to aneuploidy, which is associated with genomic instability and cell transformation. In response to aneuploidy, cells activate the tumour suppressor p53 to elicit a surveillance mechanism that halts proliferation and promotes senescence. The molecular sensors that trigger this checkpoint are unclear. Here, using a tunable system of chromosome mis-segregation, we show that mitotic errors trigger nuclear deformation, nuclear softening, and lamin and heterochromatin alterations, leading to rapid p53/p21 activation upon mitotic exit in response to changes in nuclear mechanics. We identify mTORC2 and ATR as nuclear deformation sensors upstream of p53/p21 activation. While triggering mitotic arrest, the chromosome mis-segregation-induced alterations of nuclear envelope mechanics provide a fitness advantage for aneuploid cells by promoting nuclear deformation resilience and enhancing pro-invasive capabilities. Collectively, this work identifies a nuclear mechanical checkpoint triggered by altered chromatin organization that probably plays a critical role in cellular transformation and cancer progression.

DOI: https://doi.org/10.1038/s41556-024-01565-x