Choice between 1- and 2-furrow cytokinesis in Caenorhabditis elegans embryos with tripolar spindles

Excessive centrosomes often lead to multipolar spindles, and thus probably to multipolar mitosis and aneuploidy. In Caenorhabditis elegans, ∼70% of the paternal emb-27APC6 mutant embryonic cells contained more than two centrosomes and formed multipolar spindles. However, only ~30% of the cells with tripolar spindles formed two cytokinetic furrows. The rest formed one furrow, similar to normal cells. To investigate the mechanism via which cells avoid forming two cytokinetic furrows even with a tripolar spindle, we conducted live-cell imaging in emb-27APC6 mutant cells. We observed that the chromatids were aligned on only two of the three sides of the tripolar spindle, and the angle of the tripolar spindle relative to the long axis of the cell correlated with the number of cytokinetic furrows. Our numerical modeling showed that the combination of cell shape, cortical pulling forces, and heterogeneity of centrosome size determines whether cells with a tripolar spindle form one or two cytokinetic furrows.

Multi-Omics of Aurora Inhibition Induced Polyploidy Reveals Mechanisms of Disease Relapse in MYC/BCL2-Addicted High Grade B-Cell Lymphoma

Key Points MYC mediated upregulation of TPX2, KPNA2 and RanGAP1 dysregulate the spindle assembly checkpoint in drug-induced polyploid cells. Drug-induced polyploid cells re-enter cell cycle via multipolar mitosis, fission or budding, a mechanism of disease relapse. Abstract Double-hit (DH) or double-expresser (DE) diffuse large B-cell lymphomas (DLBCL) are high-grade B-cell lymphomas that are mostly incurable with standard chemo-immunotherapy due to treatment resistance. The generation of drug-induced aneuploid/polyploid (DIAP) cells is a common effect of anti-DLBCL therapies (e.g. vincristine, doxorubicin). DIAP cells are thought to be responsible for treatment resistance, as they are capable of re-entering the cell cycle during off-therapy periods. Previously (DOI: 10.1158/1535-7163.MCT-17-0089) we demonstrated that combination of alisertib plus ibrutinib plus rituximab can partially abrogate DIAP cells and induce cell death. Here, we provide evidence that DIAP cells can re-enter the cell cycle and escape apoptosis during anti-DLBCL treatment. We also discuss MYC/BCL2 mediated molecular mechanisms that underlie treatment resistance. We isolated aneuploid/polyploid populations (2n-similar, 4n and 8n) of DH/DE-DLBCL cells after treatment with the aurora kinase (AK) inhibitor alisertib. Time-lapse microscopy of single polyploid cells (8n) revealed that following drug removal, these cells divide and proliferate by reductive cell divisions, including multipolar mitosis, meiosis-like nuclear fission and budding. Genomic, proteomic, and kinomic profiling of DIAP cells demonstrated up-regulation DNA damage, DNA replication and immune evasion pathways. In addition, the immune-kinome, AKT/MTorc1/2, and ERK/MAPK pathway are over-represented in 8n cells. Further, MYC-mediates dysregulation of the spindle assembly checkpoints by over-expression of RanGAP1, TPX2 and KPNA2. Multiple mechanisms contribute to DIAP which are amenable to novel therapeutic intervention(s) in MYC/BCL2-addicted high-grade B-cell lymphomas. Disclosures No relevant conflicts of interest to declare.

Choice between 1- and 2-furrow cytokinesis in Caenorhabditis elegans embryos with tripolar spindles

Excess numbers of centrosomes often lead to multipolar spindles, and thus probably to multipolar mitosis and aneuploidy. In Caenorhabditis elegans, approximately 70% of the paternal emb-27APC6 mutant embryonic cells contained more than 2 centrosomes and formed multipolar spindles. However, only 30% of the cells with tripolar spindles formed 2 cytokinetic furrows. The rest formed 1 furrow, like normal cells. To investigate the mechanism how the cells avoided to form 2 cytokinetic furrows even with a tripolar spindle, we conducted live-cell imaging in emb-27APC6 mutant cells. We found that the chromatids were aligned only on 2 of the 3 sides of the tripolar spindle, and the angle of the tripolar spindle relative to the long axis of the cell correlated with the number of cytokinetic furrow. Our numerical modeling showed that the combination of cell shape, cortical pulling forces, and heterogeneity of centrosome size determines whether cells with tripolar spindle form 1 or 2 cytokinetic furrows.

1,2:3,4-Diepoxybutane Induces Multipolar Mitosis in Cultured Human Lymphocytes

1,3-Butadiene, a colorless gas regularly used in the production of plastics, thermoplastic resins, and styrene-butadiene rubber, poses an increased leukemia mortality risk to workers in this field. 1,3-Butadiene is also produced by incomplete combustion of motor fuels or by tobacco smoking. It is absorbed principally through the respiratory system and metabolized by several enzymes rendering 1,2:3,4-diepoxybutane (DEB), which has the highest genotoxic potency of all metabolites of 1,3-butadiene. DEB is considered a carcinogen mainly due to its high potential as clastogen, which induces structural chromosome aberrations such as sister chromatid exchanges, chromosomal breaks, and micronuclei. Due to its clastogenic effect, DEB is one of the most used agents for diagnostic studies of Fanconi anemia, a recessively inherited disease related to mutations affecting several genes involved in a common DNA repair pathway. When performing Fanconi anemia diagnostic tests in our laboratory, we have observed occasional multipolar mitosis (MM) in lymphocyte cultures exposed to 0.1 μg/ml of DEB and harvested in the absence of any mitotic spindle inhibitor. Although previous studies reported an aneugenic effect (i.e. it induces aneuploidy) of DEB, no mechanism was suggested to explain such observations. Therefore, the aim of this study was to investigate whether exposure to 0.1 μg/ml of DEB is significantly associated with the occurrence of MM. We blindly assessed the frequency of MM in lymphocyte cultures from 10 nonsmoking healthy individuals. Two series of 3 cultures were performed from each sample under different conditions: A, without DEB; B, with 0.1 μg/ml of DEB, and C, with 25 μM of mitomycin C as positive control. Cultures exposed to DEB showed higher frequencies of MM (23 of 2,000 cells) than did the unexposed ones (3 of 2,000 cells).