Watching kinetochores sweat

A simple way to get cleavage o partition cellular components into dividing daughter cells, the spindle apparatus induces the formation of a cleavage furrow, but results conflict about which specific components are required for this process. By physically dissecting the spindle apparatus in grasshopper spermato-cytes, Alsop and Zhang now show on page 383 that bundled microtubules are the only structural constituent of the spindle apparatus required for inducing cleavage. Previous work has pointed indirectly to asters, the central spindle, and chromosomal passenger proteins as essential inducers of the cleavage furrow. In the new study, the authors used micromanipulation to create pockets of cell membrane containing specific components of the spindle apparatus. As long as functional microtubules are present in these artificial cells, cleavage furrows are induced and ingress while the microtubules undergo reorganizations characteristic of metaphase, anaphase, and telophase. Alsop and Zhang stress that other components of the spindle apparatus undoubtedly influence furrow formation when they are present, but only microtubules are essential. The authors are now introducing various degrees of asymmetry in microtubule distribution in the artificial cells. The results suggest that shifting the zone where the plus-ends of spindle microtubules overlap redefines the location of the cleavage furrow. ᭿ T Microtubules (green) are sufficient to induce an ac-tin cleavage furrow (red). ven after decades of study, it is still unclear whether kinetochores or microtubules provide the motive force to pull chromosomes toward opposite poles during cell division. On page 377, Maddox et al. propose that each makes its own contribution. They find that a combination of kinetochore-generated force and poleward flux of the microtubules moves the chromosomes in Xenopus egg extracts. The authors are the first to distinguish kinetochore microtubules from other microtubules, using high-resolution fluorescent speckle microscopy and labeled kinetochore proteins. Their high-resolution view of kinetochore–microtubule interactions shows that kinetochores exist in either E Kinetochores switch from flux to pacman during mitosis. microtubule-polymerizing or-depolymerizing states. Their data help to explain why metaphase chromosomes Neural progenitors play favorites rogrammed cell death is essential for preventing hyper-proliferation during normal embryonic brain development and is also critical to the pathogenesis of several neurodegen-erative diseases. Using mouse embryonic stem cells to model neuronal differentiation, Bieberich et al. (page 469) now show that when neural progenitor cells divide, only one progeny cell survives due to asymmetric distribution of pro-and anti-apoptotic factors between daughter cells. In the developing mouse brain, apoptosis often correlates …