bims-micesi Biomed News
on Mitotic cell signalling
Issue of 2024–08–25
seven papers selected by
Valentina Piano, Uniklinik Köln
  1. Single-nucleosome imaging unveils that condensins and nucleosome-nucleosome interactions differentially constrain chromatin to organize mitotic chromosomes.
  2. A liquid-like coat mediates chromosome clustering during mitotic exit.
  3. An Arabidopsis Kinesin-14D motor is associated with midzone microtubules for spindle morphogenesis.
  4. Sumo-regulatory SENP2 controls the homeostatic squamous mitosis-differentiation checkpoint.
  5. Mechanisms of minor pole-mediated spindle bipolarization in human oocytes.
  6. RetSat stabilizes mitotic chromosome segregation in pluripotent stem cells.
  7. Embryo multinucleation: detection, possible origins, and implications for treatment.
  1. Nat Commun. 2024 Aug 21. 15(1): 7152
    Single-nucleosome imaging unveils that condensins and nucleosome-nucleosome interactions differentially constrain chromatin to organize mitotic chromosomes.
    Kayo Hibino, Yuji Sakai, Sachiko Tamura, Masatoshi Takagi, Katsuhiko Minami, Toyoaki Natsume, Masa A Shimazoe, Masato T Kanemaki, Naoko Imamoto, Kazuhiro Maeshima.
      For accurate mitotic cell division, replicated chromatin must be assembled into chromosomes and faithfully segregated into daughter cells. While protein factors like condensin play key roles in this process, it is unclear how chromosome assembly proceeds as molecular events of nucleosomes in living cells and how condensins act on nucleosomes to organize chromosomes. To approach these questions, we investigate nucleosome behavior during mitosis of living human cells using single-nucleosome tracking, combined with rapid-protein depletion technology and computational modeling. Our results show that local nucleosome motion becomes increasingly constrained during mitotic chromosome assembly, which is functionally distinct from condensed apoptotic chromatin. Condensins act as molecular crosslinkers, locally constraining nucleosomes to organize chromosomes. Additionally, nucleosome-nucleosome interactions via histone tails constrain and compact whole chromosomes. Our findings elucidate the physical nature of the chromosome assembly process during mitosis.
    DOI:  https://doi.org/10.1038/s41467-024-51454-y
  2. Mol Cell. 2024 Aug 08. pii: S1097-2765(24)00620-8. [Epub ahead of print]
    A liquid-like coat mediates chromosome clustering during mitotic exit.
    Alberto Hernandez-Armendariz, Valerio Sorichetti, Yuki Hayashi, Zuzana Koskova, Andreas Brunner, Jan Ellenberg, Anđela Šarić, Sara Cuylen-Haering.
      The individualization of chromosomes during early mitosis and their clustering upon exit from cell division are two key transitions that ensure efficient segregation of eukaryotic chromosomes. Both processes are regulated by the surfactant-like protein Ki-67, but how Ki-67 achieves these diametric functions has remained unknown. Here, we report that Ki-67 radically switches from a chromosome repellent to a chromosome attractant during anaphase in human cells. We show that Ki-67 dephosphorylation during mitotic exit and the simultaneous exposure of a conserved basic patch induce the RNA-dependent formation of a liquid-like condensed phase on the chromosome surface. Experiments and coarse-grained simulations support a model in which the coalescence of chromosome surfaces, driven by co-condensation of Ki-67 and RNA, promotes clustering of chromosomes. Our study reveals how the switch of Ki-67 from a surfactant to a liquid-like condensed phase can generate mechanical forces during genome segregation that are required for re-establishing nuclear-cytoplasmic compartmentalization after mitosis.
    Keywords:  Ki-67; RNA; anaphase; capillary forces; chromosome; mitosis; phase separation; phosphorylation; surface condensation; surfactant
    DOI:  https://doi.org/10.1016/j.molcel.2024.07.022
  3. Curr Biol. 2024 Aug 19. pii: S0960-9822(24)00923-0. [Epub ahead of print]34(16): 3747-3762.e6
    An Arabidopsis Kinesin-14D motor is associated with midzone microtubules for spindle morphogenesis.
    Xiaojiang Guo, Calvin H Huang, Takashi Akagi, Shinsuke Niwa, Richard J McKenney, Ji-Rui Wang, Yuh-Ru Julie Lee, Bo Liu.
      The acentrosomal spindle apparatus has kinetochore fibers organized and converged toward opposite poles; however, mechanisms underlying the organization of these microtubule fibers into an orchestrated bipolar array were largely unknown. Kinesin-14D is one of the four classes of Kinesin-14 motors that are conserved from green algae to flowering plants. In Arabidopsis thaliana, three Kinesin-14D members displayed distinct cell cycle-dependent localization patterns on spindle microtubules in mitosis. Notably, Kinesin-14D1 was enriched on the midzone microtubules of prophase and mitotic spindles and later persisted in the spindle and phragmoplast midzones. The kinesin-14d1 mutant had kinetochore fibers disengaged from each other during mitosis and exhibited hypersensitivity to the microtubule-depolymerizing herbicide oryzalin. Oryzalin-treated kinesin-14d1 mutant cells had kinetochore fibers tangled together in collapsed spindle microtubule arrays. Kinesin-14D1, unlike other Kinesin-14 motors, showed slow microtubule plus end-directed motility, and its localization and function were dependent on its motor activity and the novel malectin-like domain. Our findings revealed a Kinesin-14D1-dependent mechanism that employs interpolar microtubules to regulate the organization of kinetochore fibers for acentrosomal spindle morphogenesis.
    Keywords:  Arabidopsis; Kinesin-14; acentrosomal spindle; interpolar microtubules; kinetochore fibers; microtubules; spindle midzone; spindle morphogenesis
    DOI:  https://doi.org/10.1016/j.cub.2024.07.020
  4. Cell Death Dis. 2024 Aug 16. 15(8): 596
    Sumo-regulatory SENP2 controls the homeostatic squamous mitosis-differentiation checkpoint.
    Jesús Galán-Vidal, Lorena García-Gaipo, Rut Molinuevo, Samantha Dias, Alex Tsoi, Javier Gómez-Román, James T Elder, Helfrid Hochegger, Alberto Gandarillas.
      Squamous or epidermoid cancer arises in stratified epithelia but also is frequent in the non-epidermoid epithelium of the lung by unclear mechanisms. A poorly studied mitotic checkpoint drives epithelial cells bearing irreparable genetic damage into epidermoid differentiation. We performed an RNA-sequencing gene search to target unknown regulators of this response and selected the SUMO regulatory protein SENP2. Alterations of SENP2 expression have been associated with some types of cancer. We found the protein to be strongly localised to mitotic spindles of freshly isolated human epidermal cells. Primary cells rapidly differentiated after silencing SENP2 with specific shRNAs. Loss of SENP2 produced in synchronised epithelial cells delays in mitotic entry and exit and defects in chromosomal alignment. The results altogether strongly argue for an essential role of SENP2 in the mitotic spindle and hence in controlling differentiation. In addition, the expression of SENP2 displayed an inverse correlation with the immuno-checkpoint biomarker PD-L1 in a pilot collection of aggressive lung carcinomas. Consistently, metastatic head and neck cancer cells that do not respond to the mitosis-differentiation checkpoint were resistant to depletion of SENP2. Our results identify SENP2 as a novel regulator of the epithelial mitosis-differentiation checkpoint and a potential biomarker in epithelial cancer.
    DOI:  https://doi.org/10.1038/s41419-024-06969-z
  5. Science. 2024 Aug 23. 385(6711): eado1022
    Mechanisms of minor pole-mediated spindle bipolarization in human oocytes.
    Tianyu Wu, Yuxi Luo, Meiling Zhang, Biaobang Chen, Xingzhu Du, Hao Gu, Siyuan Xie, Zhiqi Pan, Ran Yu, Ruiqi Hai, Xiangli Niu, Guimin Hao, Liping Jin, Juanzi Shi, Xiaoxi Sun, Yanping Kuang, Wen Li, Qing Sang, Lei Wang.
      Spindle bipolarization, the process of a microtubule mass transforming into a bipolar spindle, is a prerequisite for accurate chromosome segregation. In contrast to mitotic cells, the process and mechanism of spindle bipolarization in human oocytes remains unclear. Using high-resolution imaging in more than 1800 human oocytes, we revealed a typical state of multipolar intermediates that form during spindle bipolarization and elucidated the mechanism underlying this process. We found that the minor poles formed in multiple kinetochore clusters contribute to the generation of multipolar intermediates. We further determined the essential roles of HAUS6, KIF11, and KIF18A in spindle bipolarization and identified mutations in these genes in infertile patients characterized by oocyte or embryo defects. These results provide insights into the physiological and pathological mechanisms of spindle bipolarization in human oocytes.
    DOI:  https://doi.org/10.1126/science.ado1022
  6. Cell Mol Life Sci. 2024 Aug 22. 81(1): 366
    RetSat stabilizes mitotic chromosome segregation in pluripotent stem cells.
    Wanzhi Cai, Xiaoqing Yao, Gaojing Liu, Xiuyun Liu, Bo Zhao, Peng Shi.
       BACKGROUND: Chromosome stability is crucial for homeostasis of pluripotent stem cells (PSCs) and early-stage embryonic development. Chromosomal defects may raise carcinogenic risks in regenerative medicine when using PSCs as original materials. However, the detailed mechanism regarding PSCs chromosome stability maintenance is not fully understood.
    METHODS: Mouse embryonic stem cells (line D3) and human embryonic stem cells (line H9) were cultured under standard conditions. To confirm the loading of RetSat protein on mitotic chromosomes of PSCs, immunostaining was performed in PSCs spontaneous differentiation assay and iPSC reprogramming assay from mouse embryonic fibroblasts (MEFs), respectively. In addition, qPCR, immunoprecipitation, LC-MS/MS and immunoblotting were used to study the expression of RetSat, and interactions of RetSat with cohesin/condensin components. RNA sequencing and teratoma formation assay was conducted to evaluate the carcinogenic risk of mouse embryonic stem cells with RetSat deletion.
    RESULTS: We reported a PSC high-expressing gene, RetSat, plays key roles in chromosome stabilization. We identified RetSat protein localizing onto mitotic chromosomes specifically in stemness positive cells such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). We found dramatic chromosome instability, e.g. chromosome bridging, lagging and interphase micronuclei in mouse and human ESCs when down regulating RetSat. RetSat knock-out mouse ESCs upregulated cancer associated gene pathways, and displayed higher tumorigenic capacities in teratoma formation assay. Mechanistically, we confirmed that RetSat interacts with cohesin/condensin components Smc1a and Nudcd2. RetSat deletion impaired the chromosome loading dosage of Smc1a, Smc3 and Nudcd2.
    CONCLUSIONS: In summary, we reported RetSat to be a key stabilizer of chromosome condensation in pluripotent stem cells. This highlights the crucial roles of RetSat in early-stage embryonic development, and potential value of RetSat as an effective biomarker for assessing the quality of pluripotent stem cells.
    Keywords:  Carcinogenesis; Chromosome loading; Chromosome mis-segregation; Retinol saturase
    DOI:  https://doi.org/10.1007/s00018-024-05413-x
  7. Hum Reprod. 2024 Aug 22. pii: deae186. [Epub ahead of print]
    Embryo multinucleation: detection, possible origins, and implications for treatment.
    Giovanni Coticchio, Cristina Lagalla, Marilena Taggi, Danilo Cimadomo, Laura Rienzi.
      Cell cycle regulation is crucial to assure expansion of a cell population, while preserving genome integrity. This notion is especially relevant to fertilization and early embryo development, a time when the cell cycle transforms from meiotic into mitotic cycles. Zygote-to-embryo transition is acutely error-prone, causing major developmental perturbations, including cleavage delays, tri- and multi-chotomous cleavages, and cell fragmentation. Another such alteration is bi- and multinucleation, consisting of the simultaneous formation of two or more nuclei at interphase. Indeed, multinucleation affects a large proportion of early human embryos, typically at the two-cell stage. Mechanistically, several factors, including spindle dysfunction, failed cleavage, and cell fusion, may generate this cell anomaly. In assisted reproduction treatment, multinucleation is associated with reduced developmental rates and lower implantation rates in Days 2-3 embryo transfers. However, many multinucleated embryos can develop to the blastocyst stage. In blastocyst transfers, the current evidence does not suggest a major impact of a previous history of multinucleation on the odds of euploidy or successful treatment outcomes. Human embryo multinucleation remains a not-fully-understood but developmentally relevant and intriguing phenomenon which requires further research of its generative mechanisms and clinical implications.
    Keywords:  blastocyst; blastomere; cell cycle; embryo; multinucleation; nucleus
    DOI:  https://doi.org/10.1093/humrep/deae186
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