Dynein prevents erroneous kinetochore-microtubule attachments in mitosis

<p>Equal distribution of the genetic material during cell division relies on efficient congression of chromosomes to the metaphase plate. Prior to their alignment, the Dynein motor recruited to kinetochores transports a fraction of laterally-attached chromosomes along microtubules toward the spindle poles. By doing that, Dynein not only contributes to chromosome movements, but also prevents premature stabilization of end-on kinetochore-microtubule attachments. This is achieved by 2 parallel mechanisms: 1) Dynein-mediated poleward movement of chromosomes counteracts opposite polar-ejection forces (PEFs) on chromosome arms by the microtubule plus-end-directed motors chromokinesins. Otherwise, they could stabilize erroneous syntelic kinetochore-microtubule attachments and lead to the random ejection of chromosomes away from the spindle poles; and 2) By transporting chromosomes to the spindle poles, Dynein brings the former to the zone of highest Aurora A kinase activity, further destabilizing kinetochore-microtubule attachments. Thus, Dynein plays an important role in keeping chromosome segregation error-free by preventing premature stabilization of kinetochore-microtubule attachments near the spindle poles.</p

Aurora B activity is normal in cHL small and large cells.

<p>A-F. Immunofluorescence images of small mononucleated cells (A-E) and large cell undergoing mitosis (F). A. Cell in prometaphase with Aurora B kinase properly localized at centromeres and phospho-Ser10-histone H3 on chromatin. B. One cell in telophase (left) and one cell in the last stages of cytokinesis (right). Aurora B localizes properly in the central spindle or in the thin intercellular bridge that connects the two sister cells, respectively. As expected, signal for phospho-Ser10-histone H3 is only observed in the cell on the left where nuclear envelope has not reformed yet. C. Cell in prometaphase with most of the chromosomes aligned at the metaphase plate and one mono-oriented chromosome on the spindle pole with the unattached kinetochore showing prominent accumulation of auto-phosphorylated Aurora B (white arrow). Asterisk indicates a spindle pole that is unspecifically labeled by the P-T232-Aurora B antibody. D. Cell in the last stages of cytokinesis with chromatin present in the intercellular bridge (white arrowhead). Auto-phosphorylated Aurora B accumulates on the intercellular bridge revealing that Aurora B has been properly activated at a time when abscission is taking place. E. Cell in telophase with chromatin bridges staining positive for phospho-Ser10-histone H3. F. Large cell with a double metaphase plate showing auto-phosphorylated Aurora B and therefore active kinase on centromeres. Asterisks are the spindle poles. Size bar is 5 μm.</p

Binucleated RS cells form by failure of abscission.

<p>Time lapse video imaging of KMH2 cells undergoing cell division. Shown are selected DIC still images. Time is in hours:minutes:seconds. Time zero is anaphase in A,B,D,E and timepoint after nuclear envelope breakdown in C. <b>A.</b> 88% of the cells divide successfully giving rise to two daughter cells. <b>B.</b> 3.2% of the cells seem to complete cell division but maintain an intercellular bridge connecting the two cells (white arrow) that later broadens up leading to the formation of binucleated cells. <b>C.</b> 8% of cells undergo apoptotic death during mitosis. <b>D.</b> < 1% of sister cells appear to fuse but actually remain separate, as the cells round up separately for the following mitosis. <b>E.</b> Small mononucleated cell undergoing cell division and failing cytokinesis after completing furrow ingression. The two daughter cells are still connected by the midbody (white arrows), when the furrow regresses. Black arrow points at chromosomal bridges during anaphase. Size bar is 10 μm.</p