bims-micesi 2025-01-19 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2025–01–19
eleven papers selected by
Valentina Piano, Uniklinik Köln

The dependence of shugoshin on Bub1-kinase activity is dispensable for the maintenance of spindle assembly checkpoint response in Cryptococcus neoformans.
Organization of the chromosomal passenger complex clusters at inner centromeres in mitosis.
The cell cycle oscillator and spindle length set the speed of chromosome separation in Drosophila embryos.
Mitotic chromatin marking governs the segregation of DNA damage.
Centromere inactivation during aging can be rescued in human cells.
The KNL-1/Knl1 outer kinetochore protein caught regulating F-actin.
The microtubule-severing enzyme spastin regulates spindle dynamics to promote chromosome segregation in Trypanosoma brucei.
The C. elegans homolog of Sjögren's Syndrome Nuclear Antigen 1 is required for the structural integrity of the centriole and bipolar mitotic spindle assembly.
SYS-1/beta-catenin inheritance and regulation by Wnt-signaling during asymmetric cell division.
Diverse microtubule-binding repeats regulate TPX2 activities at distinct locations within the spindle.
Loss of HNRNPK During Cell Senescence Linked to Reduced Production of CDC20.

PLoS Genet. 2025 Jan 13. 21(1): e1011552

The dependence of shugoshin on Bub1-kinase activity is dispensable for the maintenance of spindle assembly checkpoint response in Cryptococcus neoformans.

Satya Dev Polisetty, Krishna Bhat, Kuladeep Das, Ivan Clark, Kevin G Hardwick, Kaustuv Sanyal.

During chromosome segregation, the spindle assembly checkpoint (SAC) detects errors in kinetochore-microtubule attachments. Timely activation and maintenance of the SAC until defects are corrected is essential for genome stability. Here, we show that shugoshin (Sgo1), a conserved tension-sensing protein, ensures the maintenance of SAC signals in response to unattached kinetochores during mitosis in a basidiomycete budding yeast Cryptococcus neoformans. Sgo1 maintains optimum levels of Aurora B kinase Ipl1 and protein phosphatase 1 (PP1) at kinetochores. The absence of Sgo1 results in the loss of Aurora BIpl1 with a concomitant increase in PP1 levels at kinetochores. This leads to a premature reduction in the kinetochore-bound Bub1 levels and early termination of the SAC signals. Intriguingly, the kinase function of Bub1 is dispensable for shugoshin's subcellular localization. Sgo1 is predominantly localized to spindle pole bodies (SPBs) and along the mitotic spindle with a minor pool at kinetochores. In the absence of proper kinetochore-microtubule attachments, Sgo1 reinforces the Aurora B kinaseIpl1-PP1 phosphatase balance, which is critical for prolonged maintenance of the SAC response.

DOI: https://doi.org/10.1371/journal.pgen.1011552
Curr Opin Cell Biol. 2025 Jan 15. pii: S0955-0674(24)00141-8. [Epub ahead of print]92 102462

Organization of the chromosomal passenger complex clusters at inner centromeres in mitosis.

Saho Matsui, Ryu-Suke Nozawa, Toru Hirota.

Stable transmission of the genome during cell division is crucial for all life forms and is universally achieved by Aurora B-mediated error correction of the kinetochore-microtubule attachments. Aurora B is the enzymatic subunit of the tetrameric protein complex called the chromosomal passenger complex (CPC), and its centromeric enrichment is required for Aurora B to ensure accurate chromosome segregation. How cells enrich the CPC at centromeres is therefore an outstanding question to be elucidated. We review our recent understanding of how CPCs are assembled at inner centromeres in mitosis, the mechanism depending on mitotic histone phosphorylations and beyond.

DOI: https://doi.org/10.1016/j.ceb.2024.102462
Curr Biol. 2025 Jan 04. pii: S0960-9822(24)01587-2. [Epub ahead of print]

The cell cycle oscillator and spindle length set the speed of chromosome separation in Drosophila embryos.

Yitong Xu, Anna Chao, Melissa Rinaldin, Alison Kickuth, Jan Brugués, Stefano Di Talia.

  Anaphase is tightly controlled spatiotemporally to ensure proper separation of chromosomes.1,2,3 The mitotic spindle, the self-organized microtubule structure driving chromosome segregation, scales in size with the available cytoplasm.4,5,6,7 Yet, the relationship between spindle size and chromosome movement remains poorly understood. Here, we address this relationship during the cleavage divisions of the Drosophila blastoderm. We show that the speed of chromosome separation gradually decreases during the four nuclear divisions of the blastoderm. This reduction in speed is accompanied by a similar reduction in spindle length, ensuring that these two quantities are tightly linked. Using a combination of genetic and quantitative imaging approaches, we find that two processes contribute to controlling the speed at which chromosomes move in anaphase: the activity of molecular motors important for microtubule depolymerization and sliding and the cell cycle oscillator. Specifically, we found that the levels of multiple kinesin-like proteins important for microtubule depolymerization, as well as kinesin-5, contribute to setting the speed of chromosome separation. This observation is further supported by the scaling of poleward flux rate with the length of the spindle. Perturbations of the cell cycle oscillator using heterozygous mutants of mitotic kinases and phosphatases revealed that the duration of anaphase increases during the blastoderm cycles and is the major regulator of chromosome velocity. Thus, our work suggests a link between the biochemical rate of mitotic exit and the forces exerted by the spindle. Collectively, we propose that the cell cycle oscillator and spindle length set the speed of chromosome separation in anaphase.

Keywords:  Drosophila embryo; anaphase; cell cycle; kinesin; microtubule; mitosis; mitotic kinases; mitotic phosphatases; spindle length

DOI:  https://doi.org/10.1016/j.cub.2024.11.046
Nat Commun. 2025 Jan 16. 16(1): 746

Mitotic chromatin marking governs the segregation of DNA damage.

Juliette Ferrand, Juliette Dabin, Odile Chevallier, Matteo Kane-Charvin, Ariana Kupai, Joel Hrit, Scott B Rothbart, Sophie E Polo.

The faithful segregation of intact genetic material and the perpetuation of chromatin states through mitotic cell divisions are pivotal for maintaining cell function and identity across cell generations. However, most exogenous mutagens generate long-lasting DNA lesions that are segregated during mitosis. How this segregation is controlled is unknown. Here, we uncover a mitotic chromatin-marking pathway that governs the segregation of UV-induced damage in human cells. Our mechanistic analyses reveal two layers of control: histone ADP-ribosylation, and the incorporation of newly synthesized histones at UV damage sites, that both prevent local mitotic phosphorylations on histone H3 serine residues. Functionally, this chromatin-marking pathway controls the segregation of UV damage in the cell progeny with consequences on daughter cell fate. We propose that this mechanism may help preserve the integrity of stem cell compartments during asymmetric cell divisions.

DOI: https://doi.org/10.1038/s41467-025-56090-8
Mol Cell. 2025 Jan 08. pii: S1097-2765(24)01035-9. [Epub ahead of print]

Centromere inactivation during aging can be rescued in human cells.

Sweta Sikder, Songjoon Baek, Truman McNeil, Yamini Dalal.

  Aging involves a range of genetic, epigenetic, and physiological alterations. A key characteristic of aged cells is the loss of global heterochromatin, accompanied by a reduction in canonical histone levels. In this study, we track the fate of centromeres in aged human fibroblasts and tissues and in various cellular senescent models. Our findings reveal that the centromeric histone H3 variant CENP-A is downregulated in aged cells in a p53-dependent manner. We observe repression of centromeric noncoding transcription through an epigenetic mechanism via recruitment of a lysine-specific demethylase 1 (LSD1/KDM1A) to centromeres. This suppression results in defective de novo CENP-A loading at aging centromeres. By dual inhibition of p53 and LSD1/KDM1A in aged cells, we mitigate the reduction in centromeric proteins and centromeric transcripts, leading to the mitotic rejuvenation of these cells. These results offer insights into a unique mechanism for centromeric inactivation during aging and provide potential strategies to reactivate centromeres.

Keywords:  CENP-A; aging; cancer; centromere; chromatin; genome instability; histone demethylase; non-coding transcription; p53; senescence

DOI:  https://doi.org/10.1016/j.molcel.2024.12.018
J Cell Biol. 2025 Feb 03. pii: e202412191. [Epub ahead of print]224(2):

The KNL-1/Knl1 outer kinetochore protein caught regulating F-actin.

Hannes E Bülow.

Kinetochores are multiprotein complexes that link chromosomes to microtubules and are essential for chromosome segregation during cell divisions. In this issue, Alves Domingos et al. (https://doi.org/10.1083/jcb.202311147) show that the conserved KNL-1/Knl1 protein of the Knl1/Mis12/Ndc80 (KMN) outer kinetochore complex postmitotically regulates F-actin to shape somatosensory dendrites.

DOI: https://doi.org/10.1083/jcb.202412191
bioRxiv. 2025 Jan 03. pii: 2025.01.03.631140. [Epub ahead of print]

The microtubule-severing enzyme spastin regulates spindle dynamics to promote chromosome segregation in Trypanosoma brucei.

Thiago Souza Onofre, Qing Zhou, Ziyin Li.

Microtubule-severing enzymes play essential roles in regulating diverse cellular processes, including mitosis and cytokinesis, by modulating microtubule dynamics. In the early branching protozoan parasite Trypanosoma brucei , microtubule-severing enzymes are involved in cytokinesis and flagellum length control during different life cycle stages, but none of them have been found to regulate mitosis in any life cycle form. Here, we report the biochemical and functional characterization of the microtubule-severing enzyme spastin in the procyclic form of T. brucei . We demonstrate that spastin catalyzes microtubule severing in vitro and ectopic overexpression of spastin disrupts spindle microtubules in vivo in trypanosome cells, leading to defective chromosome segregation. Knockdown of spastin impairs spindle integrity and disrupts chromosome alignment in metaphase and chromosome segregation in anaphase. We further show that the function of spastin requires the catalytic AAA-ATPase domain, the microtubule-binding domain, and the microtubule interacting and trafficking domain, and that the association of spastin with spindle depends on the microtubule-binding domain. Together, these results uncover an essential role for spastin in chromosome segregation by regulating spindle dynamics in this unicellular eukaryote.

DOI: https://doi.org/10.1101/2025.01.03.631140
bioRxiv. 2024 Oct 04. pii: 2024.10.03.616528. [Epub ahead of print]

The C. elegans homolog of Sjögren's Syndrome Nuclear Antigen 1 is required for the structural integrity of the centriole and bipolar mitotic spindle assembly.

Jason A Pfister, Lorenzo Agostini, Lorène Bournonville, Prabhu Sankaralingam, Zachary G Bell, Virginie Hamel, Paul Guichard, Christian Biertümpfel, Naoko Mizuno, Kevin F O'Connell.

Centrioles play central roles in ciliogenesis and mitotic spindle assembly. Once assembled, centrioles exhibit long-term stability, a property essential for maintaining numerical control. How centriole stability is achieved and how it is lost in certain biological contexts are still not completely understood. In this study we show that SSNA-1, the Caenorhabditis elegans ortholog of Sjogren's Syndrome Nuclear Antigen 1, is a centriole constituent that localizes close to the microtubule outer wall, while also exhibiting a developmentally regulated association with centriole satellite-like structures. A complete deletion of the ssna-1 gene results in an embryonic lethal phenotype marked by the appearance of extra centrioles and spindle poles. We show that SSNA-1 genetically interacts with the centriole stability factor SAS-1 and is required post assembly for centriole structural integrity. In SSNA-1's absence, centrioles assemble but fracture leading to extra spindle poles. However, if the efficiency of cartwheel assembly is reduced, the absence of SSNA-1 results in daughter centriole loss and monopolar spindle formation, indicating that the cartwheel and SSNA-1 cooperate to stabilize the centriole during assembly. Our work thus shows that SSNA-1 contributes to centriole stability during and after assembly, thereby ensuring proper centriole number.

DOI: https://doi.org/10.1101/2024.10.03.616528
Mol Biol Cell. 2025 Jan 15. mbcE24100441

SYS-1/beta-catenin inheritance and regulation by Wnt-signaling during asymmetric cell division.

Maria F Valdes Michel, Bryan T Phillips.

Asymmetric cell division (ACD) allows daughter cells of a polarized mother to acquire different developmental fates. In C. elegans, the Wnt/β-catenin Asymmetry (WβA) pathway regulates many embryonic and larval ACDs; here, a Wnt gradient induces an asymmetric distribution of Wnt signaling components within the dividing mother cell. One terminal nuclear effector of the WβA pathway is the transcriptional activator SYS-1/β-catenin. SYS-1 is sequentially negatively regulated during ACD; first by centrosomal regulation and subsequent proteasomal degradation and second by asymmetric activity of the β-catenin "destruction complex" in one of the two daughter cells, which decreases SYS-1 levels in the absence of WβA signaling. However, the extent to which mother cell SYS-1 influences cell fate decisions of the daughters is unknown. Here, we quantify inherited SYS-1 in the differentiating daughter cells and the role of SYS-1 inheritance in Wnt-directed ACD. Photobleaching experiments demonstrate the GFP::SYS-1 present in daughter cell nuclei is comprised of inherited and de novo translated SYS-1 pools. We used a photoconvertible DENDRA2::SYS-1, to directly observe the dynamics of inherited SYS-1. Photoconversion during mitosis reveals that SYS-1 clearance at the centrosome preferentially degrades older SYS-1 and that newly localized centrosomal SYS-1 depends on dynein trafficking. Photoconversion of DENDRA2::SYS-1 in the EMS cell during Wnt-driven ACD shows daughter cell inheritance of mother cell SYS-1. Additionally, disrupting centrosomal SYS-1 localization in mother cells increased inherited SYS-1 and, surprisingly, loss of centrosomal SYS-1 also resulted in increased levels of de novo SYS-1 in both EMS daughter cells. Lastly, we show that negative regulation of SYS-1 in daughter cells via the destruction complex member APR-1/APC is key to limit both the de novo and the inherited SYS-1 pools in both the E and the MS cells. We conclude that regulation of both inherited and newly translated SYS-1 via centrosomal processing in the mother cell and daughter cell regulation via Wnt signaling are critical to maintain sister SYS-1 asymmetry during ACD.

DOI: https://doi.org/10.1091/mbc.E24-10-0441
J Cell Biol. 2025 Mar 03. pii: e202404025. [Epub ahead of print]224(3):

Diverse microtubule-binding repeats regulate TPX2 activities at distinct locations within the spindle.

Zhuobi Liang, Junjie Huang, Yong Wang, Shasha Hua, Kai Jiang.

TPX2 is an elongated molecule containing multiple α-helical repeats. It stabilizes microtubules (MTs), promotes MT nucleation, and is essential for spindle assembly. However, the molecular basis of how TPX2 performs these functions remains elusive. Here, we systematically characterized the MT-binding activities of all TPX2 modules individually and in combinations and investigated their respective contributions both in vitro and in cells. We show that TPX2 contains α-helical repeats with opposite preferences for "extended" and "compacted" tubulin dimer spacing, and their distinct combinations produce divergent outcomes, making TPX2 activity highly robust yet tunable. Importantly, a repeat group at the C terminus, R8-9, is the key determinant of the TPX2 function. It stabilizes MTs by promoting rescues in vitro and is critical in spindle assembly. We propose a model where TPX2 activities are spatially regulated via its diverse MT-binding repeats to accommodate its varied functions in distinct locations within the spindle. Furthermore, we reveal a synergy between TPX2 and HURP in stabilizing spindle MTs.

DOI: https://doi.org/10.1083/jcb.202404025
Mol Cell Biol. 2025 Jan 13. 1-13

Loss of HNRNPK During Cell Senescence Linked to Reduced Production of CDC20.

Chang Hoon Shin, Martina Rossi, Krystyna Mazan-Mamczarz, Jennifer L Martindale, Rachel Munk, Apala Pal, Yulan Piao, Jinshui Fan, Supriyo De, Kotb Abdelmohsen, Myriam Gorospe.

  Cellular senescence is a complex biological response to sublethal damage. The RNA-binding protein HNRNPK was previously found to decrease prominently during senescence in human diploid fibroblasts. Here, analysis of the mechanisms leading to reduced HNRNPK abundance revealed that in cells undergoing senescence, HNRNPK mRNA levels declined transcriptionally and full-length HNRNPK protein was progressively lost, while the abundance of a truncated HNRNPK increased. The ensuing loss of full-length HNRNPK enhanced cell cycle arrest along with increased DNA damage. Analysis of the RNAs enriched after HNRNPK ribonucleoprotein immunoprecipitation (RIP) revealed a prominent target of HNRNPK, CDC20 mRNA, encoding a protein critical for progression through the G2/M phase of the cell division cycle. Silencing HNRNPK markedly decreased the levels of CDC20 mRNA via reduced transcription and stability of CDC20 mRNA, leading to lower CDC20 protein levels; conversely, overexpressing HNRNPK increased CDC20 production. Depletion of either HNRNPK or CDC20 impaired cell proliferation, with a concomitant reduction in the levels of CDK1, a key kinase for progression through G2/M. Given that overexpressing CDC20 in HNRNPK-silenced cells partly alleviated growth arrest, we propose that the reduction in HNRNPK levels in senescent cells contributed to inhibiting proliferation at least in part by suppressing CDC20 production.

Keywords:  CDC20; HNRNPK; cell cycle arrest; senescence

DOI:  https://doi.org/10.1080/10985549.2024.2443590