bims-micesi 2024-09-01 papers

Issue of 2024–09–01
six papers selected by
Valentina Piano, Uniklinik Köln

J Cell Biol. 2024 Nov 04. pii: e202401169. [Epub ahead of print]223(11):

Aurora B controls anaphase onset and error-free chromosome segregation in trypanosomes.

Daniel Ballmer, Hua Jane Lou, Midori Ishii, Benjamin E Turk, Bungo Akiyoshi.

Kinetochores form the interface between chromosomes and spindle microtubules and are thus under tight control by a complex regulatory circuitry. The Aurora B kinase plays a central role within this circuitry by destabilizing improper kinetochore-microtubule attachments and relaying the attachment status to the spindle assembly checkpoint. Intriguingly, Aurora B is conserved even in kinetoplastids, a group of early-branching eukaryotes which possess a unique set of kinetochore proteins. It remains unclear how their kinetochores are regulated to ensure faithful chromosome segregation. Here, we show in Trypanosoma brucei that Aurora B activity controls the metaphase-to-anaphase transition through phosphorylation of the divergent Bub1-like protein KKT14. Depletion of KKT14 overrides the metaphase arrest resulting from Aurora B inhibition, while expression of non-phosphorylatable KKT14 delays anaphase onset. Finally, we demonstrate that re-targeting Aurora B to the outer kinetochore suffices to promote mitotic exit but causes extensive chromosome missegregation in anaphase. Our results indicate that Aurora B and KKT14 are involved in an unconventional circuitry controlling cell cycle progression in trypanosomes.

DOI: https://doi.org/10.1083/jcb.202401169

Cells. 2024 Aug 22. pii: 1397. [Epub ahead of print]13(16):

Contribution of AurkA/TPX2 Overexpression to Chromosomal Imbalances and Cancer.

Federica Polverino, Anna Mastrangelo, Giulia Guarguaglini.

The AurkA serine/threonine kinase is a key regulator of cell division controlling mitotic entry, centrosome maturation, and chromosome segregation. The microtubule-associated protein TPX2 controls spindle assembly and is the main AurkA regulator, contributing to AurkA activation, localisation, and stabilisation. Since their identification, AurkA and TPX2 have been described as being overexpressed in cancer, with a significant correlation with highly proliferative and aneuploid tumours. Despite the frequent occurrence of AurkA/TPX2 co-overexpression in cancer, the investigation of their involvement in tumorigenesis and cancer therapy resistance mostly arises from studies focusing only on one at the time. Here, we review the existing literature and discuss the mitotic phenotypes described under conditions of AurkA, TPX2, or AurkA/TPX2 overexpression, to build a picture that may help clarify their oncogenic potential through the induction of chromosome instability. We highlight the relevance of the AurkA/TPX2 complex as an oncogenic unit, based on which we discuss recent strategies under development that aim at disrupting the complex as a promising therapeutic perspective.

Keywords: aneuploidy; centrosomes; chromosome instability; microtubules; mitosis

DOI: https://doi.org/10.3390/cells13161397

J Cell Biol. 2024 Nov 04. pii: e202403165. [Epub ahead of print]223(11):

Near millimolar concentration of nucleosomes in mitotic chromosomes from late prometaphase into anaphase.

Fernanda Cisneros-Soberanis, Eva L Simpson, Alison J Beckett, Nina Pucekova, Samuel Corless, Natalia Y Kochanova, Ian A Prior, Daniel G Booth, William C Earnshaw.

Chromosome compaction is a key feature of mitosis and critical for accurate chromosome segregation. However, a precise quantitative analysis of chromosome geometry during mitotic progression is lacking. Here, we use volume electron microscopy to map, with nanometer precision, chromosomes from prometaphase through telophase in human RPE1 cells. During prometaphase, chromosomes acquire a smoother surface, their arms shorten, and the primary centromeric constriction is formed. The chromatin is progressively compacted, ultimately reaching a remarkable nucleosome concentration of over 750 µM in late prometaphase that remains relatively constant during metaphase and early anaphase. Surprisingly, chromosomes then increase their volume in late anaphase prior to deposition of the nuclear envelope. The plateau of total chromosome volume from late prometaphase through early anaphase described here is consistent with proposals that the final stages of chromatin condensation in mitosis involve a limit density, such as might be expected for a process involving phase separation.

DOI: https://doi.org/10.1083/jcb.202403165

Proc Natl Acad Sci U S A. 2024 Sep 03. 121(36): e2403153121

Orientation-independent-DIC imaging reveals that a transient rise in depletion attraction contributes to mitotic chromosome condensation.

Shiori Iida, Satoru Ide, Sachiko Tamura, Masaki Sasai, Tomomi Tani, Tatsuhiko Goto, Michael Shribak, Kazuhiro Maeshima.

Genomic information must be faithfully transmitted into two daughter cells during mitosis. To ensure the transmission process, interphase chromatin is further condensed into mitotic chromosomes. Although protein factors like condensins and topoisomerase IIα are involved in the assembly of mitotic chromosomes, the physical bases of the condensation process remain unclear. Depletion attraction/macromolecular crowding, an effective attractive force that arises between large structures in crowded environments around chromosomes, may contribute to the condensation process. To approach this issue, we investigated the "chromosome milieu" during mitosis of living human cells using an orientation-independent-differential interference contrast module combined with a confocal laser scanning microscope, which is capable of precisely mapping optical path differences and estimating molecular densities. We found that the molecular density surrounding chromosomes increased with the progression from prophase to anaphase, concurring with chromosome condensation. However, the molecular density went down in telophase, when chromosome decondensation began. Changes in the molecular density around chromosomes by hypotonic or hypertonic treatment consistently altered the condensation levels of chromosomes. In vitro, native chromatin was converted into liquid droplets of chromatin in the presence of cations and a macromolecular crowder. Additional crowder made the chromatin droplets stiffer and more solid-like. These results suggest that a transient rise in depletion attraction, likely triggered by the relocation of macromolecules (proteins, RNAs, and others) via nuclear envelope breakdown and by a subsequent decrease in cell volumes, contributes to mitotic chromosome condensation, shedding light on a different aspect of the condensation mechanism in living human cells.

Keywords: OI-DIC; chromatin; depletion attraction; liquid droplets; mitotic chromosome condensation

DOI: https://doi.org/10.1073/pnas.2403153121

Appl Plant Sci. 2024 Jul-Aug;12(4):12(4): e11588

Unfurling an improved method for visualizing mitotic chromosomes in ferns.

Rosa Ramirez-Castillo, Claudio Palma-Rojas, Pedro Jara Seguel, Amanda L Grusz, Cristian Araya-Jaime.

Premise: Cytotaxonomy employs chromosome visualization to study organismal relationships and evolution. Despite the critical value of cytogenetic data, cytotypes are lacking for many plant groups. Here, we present an improved approach for visualizing mitotic chromosomes in ferns, a key lineage of land plants, using the dividing cells of unfurling croziers (fiddleheads).
Methods and Results: Our modified mitotic chromosome preparation incorporates a brief pectinase-cellulase pretreatment, as well as colchicine fixation and the Feulgen reaction to improve the staining and separation of mitotic chromosomes. To demonstrate this easy and efficient assessment, we determined the sporophytic (2n) chromosome number for three fern species: Cheilanthes mollis (2n = 60), Cheilanthes hypoleuca (2n = 120), and Nephrolepis cordifolia (2n = 82).
Conclusions: The new method presented here improves visualizations of mitotic chromosomes from the dividing nuclei of young fern croziers. Fiddleheads are widely accessible in nature and in living collections worldwide, and this modified approach increases their suitability for fern cytotaxonomic studies.

Keywords: Cheilanthes hypoleuca; Cheilanthes mollis; Cheilanthoideae; Nephrolepidaceae; Nephrolepis cordifolia; cytology; karyotype; whole‐genome duplication

DOI: https://doi.org/10.1002/aps3.11588

J Med Chem. 2024 Aug 27.

Selective Aurora A-TPX2 Interaction Inhibitors Have In Vivo Efficacy as Targeted Antimitotic Agents.

Aurora A kinase, a cell division regulator, is frequently overexpressed in various cancers, provoking genome instability and resistance to antimitotic chemotherapy. Localization and enzymatic activity of Aurora A are regulated by its interaction with the spindle assembly factor TPX2. We have used fragment-based, structure-guided lead discovery to develop small molecule inhibitors of the Aurora A-TPX2 protein-protein interaction (PPI). Our lead compound, CAM2602, inhibits Aurora A:TPX2 interaction, binding Aurora A with 19 nM affinity. CAM2602 exhibits oral bioavailability, causes pharmacodynamic biomarker modulation, and arrests the growth of tumor xenografts. CAM2602 acts by a novel mechanism compared to ATP-competitive inhibitors and is highly specific to Aurora A over Aurora B. Consistent with our finding that Aurora A overexpression drives taxane resistance, these inhibitors synergize with paclitaxel to suppress the outgrowth of pancreatic cancer cells. Our results provide a blueprint for targeting the Aurora A-TPX2 PPI for cancer therapy and suggest a promising clinical utility for this mode of action.

DOI: https://doi.org/10.1021/acs.jmedchem.4c01165