bims-micesi Biomed News
on Mitotic cell signalling
Issue of 2025–10–12
ten papers selected by
Valentina Piano, Uniklinik Köln



  1. J Biol Chem. 2025 Oct 04. pii: S0021-9258(25)02637-7. [Epub ahead of print] 110785
      MYCBP2 (PAM) is a large signalling hub that plays a key role in various processes, including neuronal connectivity and growth, cell division, and protein ubiquitination. Together with the substrate specificity factor FBXO45, MYCBP2 forms an E3 ligase complex that is involved in mitotic cell fate decision. During extended mitotic arrest caused by anti-microtubule drugs, cells may either experience cell death or escape mitosis through mitotic slippage. E3 ligase mediated ubiquitination is antagonized by deubiquitinating enzymes (DUBs). In this study, we show that despite their opposing activities, DUB-E3 ligase complexes can form and cooperate. We identify an E3 ligase complex consisting of MYCBP2 and a new substrate specificity factor, SPRYD3. Interestingly, SPRYD3-MYCBP2 promotes bipolar spindle formation by facilitating non-canonical ubiquitination on the DUB USP11 cysteine 318. We find that this process promotes bipolar spindle formation and mitotic slippage in presence of microtubule targeting drugs.
    Keywords:  E3 ligase; MYCBP2; SPRYD3/ ubiquitination; USP11; deubiquitinase; mitotic cell fate; spindle assembly
    DOI:  https://doi.org/10.1016/j.jbc.2025.110785
  2. J Comput Aided Mol Des. 2025 Oct 11. 39(1): 92
      Microtubules are crucial components of the mitotic spindle, essential in chromosome segregation during cell division. EG5, a kinesin motor protein, has emerged as a critical player in this process by promoting the separation of sister chromatids. Dysregulation of EG5 function is associated with tumorigenesis, making it a promising target for cancer therapeutics. Hence, understanding EG5's molecular mechanisms is a key to developing better therapies with fewer side effects. Here, we investigate the mechanisms by which EG5 interacts with microtubules and how this interaction enhances its motor activity. Utilizing computational methods, we probe the role of microtubule binding in the allosteric regulation of EG5 dynamics. Our results demonstrate that microtubule binding significantly enhances EG5's dynamic flexibility and motor activity, while inhibitors targeting distinct allosteric sites disrupt this interaction. These insights provide a molecular framework for the rational design of EG5-targeted inhibitors, with potential implications for anticancer drug development.
    Keywords:  All-atom molecular dynamics; Cancer; Cell division; Coarse grain dynamics; Kinesins; Microtubule-EG5 complex
    DOI:  https://doi.org/10.1007/s10822-025-00670-9
  3. Cell Death Dis. 2025 Oct 07. 16(1): 707
      TRIM8 is an E3 ubiquitin ligase that functions as both a tumour suppressor and an oncoprotein. Earlier, we reported that TRIM8 interacts with key regulators of mitotic spindle assembly, and that TRIM8 knockdown results in mitotic delay and aneuploidy. In this study, we implemented an omics strategy with differential transcriptomic (single-cell RNA sequencing or scRNA-seq), translatomic (polysome profiling with RNA-seq), and proteomic (LC-MS/MS) approaches to elucidate the involvement of TRIM8 in different levels (transcription, translation, post-translation) and stages (G0/G1, S, G2/M) of mitotic cell cycle regulation and progression. With the aid of differential transcriptomic and proteomic approaches, we show that depletion of TRIM8 perturbs the canonical 'Cell Cycle Control of Chromosomal Replication' pathway. Furthermore, TRIM8 downregulation induces alterations in the translation activity of cells and results in the upregulation of polysome-bound MALAT1 lncRNA by means of significant changes in polysome profiling coupled with RNA-sequencing. Moreover, we unveil for the first time endogenous TRIM8 as a novel ciliary protein that localizes with CEP170 at centrosome. Cilia analysis revealed a significant reduction in the number of ciliated cells, along with shorter cilia, in TRIM8-silenced ARPE-19 cells. Our study is the first to demonstrate the dynamic role of a TRIM family protein across multiple stages of mitosis and to define TRIM8 as a novel ciliary protein.
    DOI:  https://doi.org/10.1038/s41419-025-07973-7
  4. J Cell Sci. 2025 Oct 06. pii: jcs.264161. [Epub ahead of print]
      The meiotic spindle forms only around the chromosomes in oocytes, despite the exceptionally large volume of the cytoplasm. This spatial restriction is likely to be governed by local activation of key microtubule regulators around the chromosomes in oocytes, but the identities of these microtubule regulators and the mechanisms remain unclear. To address this, we developed a novel assay to visualise spatial regulation of spindle-associated proteins in Drosophila oocytes by inducing ectopic microtubule clusters. This assay identified several proteins including the TPX2 homologue Mei-38 that localise more strongly to microtubules near the chromosomes than away from them. In Mei-38, we identified a microtubule-binding domain containing a region highly conserved also in humans. The domain itself is regulated spatially, and contains a conserved serine and a nearby PP2A-B56 docking motif. A non-phosphorylatable mutation of this serine allows the domain to localise to ectopic microtubules as well as spindle microtubules, while mutations in a PP2A-B56 docking motif greatly reduced the spindle localisation. As this phosphatase is concentrated at the kinetochores, it may act as a novel chromosomal signal spatially regulating spindle proteins within oocytes.
    Keywords:  Drosophila; Meiosis; Oocyte; Phosphatase; Spindle
    DOI:  https://doi.org/10.1242/jcs.264161
  5. PLoS Genet. 2025 Oct 07. 21(10): e1011596
      Eukaryotic chromosome segregation relies on the assembly of a bipolar machinery based on microtubules (MTs), named the mitotic spindle. Formation of the mitotic spindle follows a force balance mechanism that ensures the proper capture and separation of sister chromatids. Many proteins have been involved in the establishment of this force balance, although kinesin 5 is well recognized as the major outward pushing force generator, since its inactivation results in monopolar, non-functional spindles. In order to find additional players in the force balance mechanism, we have performed a suppressor screen using a conditional allele of the fission yeast kinesin 5 ortholog Cut7. This screen identified that the lack of the PP6 phosphatase partially suppresses cut7 phenotypes, at least by defective translation of MT regulators, such as the minus end-directed kinesin Klp2, the MT stabilizer Alp7 and the MT bundler Ase1, impacting on the force balance mechanism. Additionally, our data show that the Elongator complex, a target activated by PP6 for efficient tRNA modification, also contributes to the force balance, albeit to a lesser extent. Importantly, this complex has recently been implicated in direct MT polymerization in metazoans, a role not shared by its fission yeast counterpart.
    DOI:  https://doi.org/10.1371/journal.pgen.1011596
  6. MicroPubl Biol. 2025 ;2025
      The nuclear envelope is composed of sheet-like ER that separates chromatin from tubulin during interphase. During oocyte maturation in C. elegans , a fenestrated envelope of sheet-like ER continues to envelope the meiotic spindle through metaphase I. ER is thus excluded from the nuclear/spindle volume during spindle assembly. To test the importance of this exclusion, we forced ER into the meiotic spindle by coupling kinesin motor domains to the ER. Forcing ER into the spindle interior caused a statistically significant increase in metaphase spindle width. Exclusion of ER from the spindle thus affects spindle geometry.
    DOI:  https://doi.org/10.17912/micropub.biology.001812
  7. MicroPubl Biol. 2025 ;2025
      The fission yeast kinesin-6 Klp9 localizes to the spindle midzone at anaphase to produce sliding forces to elongate the bipolar spindle. In the absence of Klp9 , anaphase spindle elongation is attenuated by half its normal rate. Klp9 functions as a microtubule plus end-directed tetrameric motor. Tetramerization is the key to its microtubule sliding function, as tetramerization allows Klp9 to bind antiparallel microtubules at the midzone. The amino acid sequence of Klp9 indicates two alpha-helical coiled-coils domains CC1 and CC2, important for protein-protein interactions. We seeked the potential oligomerization states of Klp9 via its coiled-coils using AlphaFold3. AlphaFold predicted that CC1 can form dimers and together with CC2 can form tetramers. The different oligomeric states enabled precise experimental verifications. We measured Klp9 motor GFP intensity and anaphase spindle elongation rate for the full-length Klp9 , Klp9-deletion (Klp9Δ), and truncated Klp9 containing no coiled-coils, or only CC1, or both CC1 and CC2. The results indicate that: 1) GFP intensity increases with increasing oligomeric state, and 2) attenuated anaphase spindle velocity is restored only in the Klp9 truncation containing both CC1 and CC2. The experimental data are consistent with prediction, indicating that CC1 contributes to Klp9 dimerization, and that CC1 and CC2 together contribute to Klp9 tetramerization.
    DOI:  https://doi.org/10.17912/micropub.biology.001829
  8. Protein Sci. 2025 Nov;34(11): e70329
      The mitotic arrest deficiency 2 (MAD2) exists in inactive and active forms under physiologic conditions. In its active conformation, MAD2 binds to the cell division cycle protein 20 (Cdc20) and prevents the separation of duplicated chromosomes. In the inactive conformation, the C-terminal region of MAD2 covers the binding motif for the Cdc20 target. Here, we investigated the MAD2 activation mechanism using structure-based models (SBMs) simulations, amino acid coevolution, and structural frustration analysis. MAD2 switches between active and inactive conformations while maintaining core stability. Simulations reveal an intermediate state during the transition consistent with recent time-resolved NMR experiments. Coevolution analysis captures native contacts for both states. These native contacts, present in both conformations, compete, driving transitions between different protein states. This competition leads to a frustrated energy landscape. Frustration analysis further shows that highly frustrated residues are present in both conformations, particularly in the fold-switching segments.
    Keywords:  co‐evolution analysis; energy landscape; folding funnel; fold‐switching proteins; frustration; structure‐based models
    DOI:  https://doi.org/10.1002/pro.70329
  9. J Microsc. 2025 Oct 11.
      Accurate detection of mitosis is crucial in automated cell analysis, yet many existing methods depend heavily on deep learning models or complex detection techniques, which can be computationally intensive and error-prone, particularly when segmentation is incomplete. This study presents a novel unsupervised method for mitosis detection, leveraging the geometric properties of the Cassini oval to reduce computational costs and enhance robustness. Our approach integrates a newly developed deep learning model, MaxSigNet, for initial cell segmentation. We subsequently employ the Cassini oval in its single-ring mode to detect mother cells in the initial frame and switch to double-ring mode in subsequent frames to identify daughter cells and confirm mitosis events. The success of this method hinges on the presence of equal non-zero foci values in the mother cell and distinct non-zero foci values in the daughter cells, which indicate accurate mitosis detection. The method was evaluated across six datasets from four different cell lines, achieving perfect F1, Recall and Precision scores on four datasets, with scores of 96% and 85% on the remaining two. Comparative analysis demonstrated that our method outperformed similar approaches in F1 and Recall metrics. Additionally, the method showed substantial robustness to incomplete segmentation, with only a 20% average drop in F1 scores when tested with older segmentation methods like K-means, Felzenszwalb and Watershed. The proposed method offers a significant advancement in mitosis detection by leveraging the Cassini oval's properties, providing a reliable and efficient solution for automated cell analysis systems. This approach promises to enhance the accuracy and efficiency of cellular behaviour studies, with potential applications in various biomedical research fields.
    Keywords:  Cassini oval; cell division; cell division detection; mitosis; mitosis detection
    DOI:  https://doi.org/10.1111/jmi.70041