Concentrating on the mitotic spindle.
Bottom Line: In eukaryotes, the microtubule-based spindle drives chromosome segregation.In this issue, Schweizer et al. (2015; J.Their results add an important new feature to the models of how this structure assembles and is regulated.
Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 email@example.com.Show MeSH
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Mentions: The mitotic spindle is known to scale with cell size: smaller cells have smaller spindles (Levy and Heald, 2012). Spindle size scaling is prominent during development when repeated cell division without embryonic growth results in cells that can be several orders of magnitude smaller than that of the zygote. Recently, cytoplasm volume and tubulin concentration was shown to be an important factor in spindle size scaling; however, a curious exception to the size scaling rule is that there seems to be an upper limit to spindle size, resulting in stable spindle size when a threshold cell size is reached (Wühr et al., 2008; Good et al., 2013; Hazel et al., 2013). A spindle envelope would provide mechanisms to maintain increased local tubulin concentration independent of the absolute amount available in the cell. The net effect would be that spindle size scales in very large cells to the spindle envelope size rather than cell size in a manner analogous to chromosome size scaling to nuclear size independently of cell size (Fig. 1 A). Clearly this is a more complex problem and factors such as tubulin protein production and polymerization cofactors (such as the Tog family of proteins) clearly play an important role (Slep, 2009). However, spindle envelope–based molecular crowding could provide an elegant solution to a biochemical problem.
Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 firstname.lastname@example.org.