Chromosomal attachments set length and microtubule number in the Saccharomyces cerevisiae mitotic spindle.
Bottom Line: The length of the mitotic spindle varies among different cell types.A simple model for spindle length regulation requires balancing two forces: pulling, due to micro-tubules that attach to the chromosomes at their kinetochores, and pushing, due to interactions between microtubules that emanate from opposite spindle poles.Electron microscopy shows that manipulating kinetochore number alters the number of spindle microtubules: adding extra kinetochores increases the number of spindle microtubules, suggesting kinetochore-based regulation of microtubule number.
Affiliation: Molecular and Cellular Biology Department, Harvard University, Cambridge, MA 02138 FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138.Show MeSH
Mentions: Cells must regulate the size of their internal structures. Some, such as viral capsids, are determined by specific molecular interactions. In others, such as the muscle sarcomere, molecular rulers set the length. The mitotic spindle is a dynamic structure whose size exceeds that of any of its individual components, and its length is set by rules that govern its self-assembly. The spindle is a bipolar array of microtubules that segregates chromosomes (Bloom and Joglekar, 2010). Microtubules attach to chromosomes through kinetochores—protein complexes assembled on centromeric DNA (Westermann et al., 2007). In metaphase, bioriented sister chromatids attach to microtubules from opposite poles and are held together by cohesin rings (Figure 1A). Anaphase chromosome segregation occurs when cohesin is cleaved and sister chromatids are pulled to opposite poles (Tanaka, 2008). Spindle lengths vary from 2 μm in budding yeast (Winey et al., 1995; Straight et al., 1997) to 60 μm in single-celled Xenopus embryos (Wühr et al., 2008), but the spindle of each cell type has a characteristic length (Goshima and Scholey, 2010).
Affiliation: Molecular and Cellular Biology Department, Harvard University, Cambridge, MA 02138 FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138.