Mitotic Spindle Assembly and Chromosome Segregation Susan L Kline-Smith, Claire E Walczak  Molecular Cell  Volume 15, Issue 3, Pages 317-327 (August 2004) DOI: 10.1016/j.molcel.2004.07.012 Copyright © 2004 Cell Press Terms and Conditions

Figure 1 Microtubule Structure and Dynamics (A) General MT structure is illustrated here with α-tubulin in orange and β-tubulin in blue. A single protofilament within the polymer lattice is outlined. (B) MTs switch between stages of polymerization and depolymerization, a behavior central to dynamic instability. Although dynamic instability can occur at both ends of the MT, only one end is shown for simplicity. GDP bound tubulin is in orange, and GTP bound tubulin, which generates the GTP cap, is in purple. Molecular Cell 2004 15, 317-327DOI: (10.1016/j.molcel.2004.07.012) Copyright © 2004 Cell Press Terms and Conditions

Figure 2 Mitotic Spindle Components This cartoon shows the basic components of the mitotic spindle in somatic cells. MTs are shown in gray, centrosomes in green, kinetochores in red, and chromosomes in blue. Positions of MT minus (−) ends versus plus (+) ends are indicated. Molecular Cell 2004 15, 317-327DOI: (10.1016/j.molcel.2004.07.012) Copyright © 2004 Cell Press Terms and Conditions

Figure 3 Global Trends in Microtubule Dynamics during Interphase and Mitosis During mitosis, large shifts in global MT dynamics take place to allow for spindle assembly. Here we have illustrated the general trends for global changes in MT properties that have been measured thus far in somatic cells. IØ, interphase; P, prophase; NEB, nuclear envelope breakdown; PM, prometaphase; M, metaphase. (A) MT plus end growth rate increases at prophase and appears to be constantly elevated during mitosis (indicated by red line). (B) Increased growth rates and decreased lengths of MTs facing away from the nucleus in prophase suggest a small increase in MT turnover in early prophase, while a dramatic increase in MT turnover occurs at NEB (indicated by green line). (C) Bulk MT polymer levels abruptly decrease at NEB during mitosis, although metaphase spindles contain MT polymer levels similar to interphase MT arrays (indicated by black line). The increase in turnover (green) and decrease in MT polymer (black) at NEB correlate to increased catastrophe and decreased rescue frequencies of astral MTs at this time. Molecular Cell 2004 15, 317-327DOI: (10.1016/j.molcel.2004.07.012) Copyright © 2004 Cell Press Terms and Conditions

Figure 4 Microtubule Flux This illustration depicts a single MT that extends from the spindle pole (left) to the kinetochore (right) in a mitotic spindle. The group of dark blue tubulin dimers represents a single “speckle,” which can be used as a fiduciary marker to measure dynamics within the spindle MT polymer. The speckle can be tracked over time to determine the rate of flux. Molecular Cell 2004 15, 317-327DOI: (10.1016/j.molcel.2004.07.012) Copyright © 2004 Cell Press Terms and Conditions

Figure 5 Microtubule Dynamics and Chromosome Movement Two mechanisms of K fiber dynamics exist to move chromosomes. Positions of major force production are indicated by large black arrows, while positions of minor force production are indicated by small gray arrows. (A) In somatic cells, MT plus end depolymerization at kinetochores (Pac-Man activity) provides most of the force for movement during congression and segregation, although flux does contribute to some extent. (B) Embryonic systems use flux-associated minus end depolymerization at poles (Moving Walkway Activity) to segregate chromosomes, although kinetochores may occasionally exhibit Pac-Man activity. Molecular Cell 2004 15, 317-327DOI: (10.1016/j.molcel.2004.07.012) Copyright © 2004 Cell Press Terms and Conditions