Mitosis

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Mitosis
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Microtubules and Motors MT polymer ratchets and
motor proteins.
F 1-50pN
F 1-10pN
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Microtubule Polymer Dynamics
Teadmilling/Flux. (Margolis and Wilson, 1978
Mitchison, 1989).
Dynamic Instability. (Mitchison and Kirschner,
1984).
vg , vs, fres, fcat
dn/dt KonC - Koff
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1953 Shinya Inoue uses polarizing light
microscopy
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Dynamic Equilibrium (Inoue, 1967). Poleward
Flux (Forer, 1965).
Steady state fibers polymerize at
equator depolymerize at poles.
Polymerize/push depolymerize/pull.
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The Spindle Machine Drosophila spindle MTs
display poleward flux AND dynamic instability.
t1/2 5s (versus Ptk t1/2 400s).

• How do microtubules and motors drive mitotic
  motility.
• How are smooth, accurate movements produced if
  the microtubule tracks are constantly growing and
  shrinking.

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E.M. analysis by McIntosh et al, 1969-80 Sliding
Filaments
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Polarity of MTs in the Spindle Interzone.
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Force Generation by Spindle Fibers.
Nicklas, 1983 1 nN stall force.
Ostegren, 1951 Force balance.

• Antagonistic poleward forces.
• Force proportional to distance
• from pole.
• Forces balance at metaphase.
• Poleward forces drive anaphase A

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(No Transcript)
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Mechanism of Anaphase A and B
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Model for Anaphase B

• Kinesin-5-dependent ipMT sliding pushes poles
  apart
• Poleward Flux is an on-off Switch

(Brust-Mascher et al, 2004, PNAS,101, 15938
Cheerambathur et al, 2007, JCB, 177, 995)
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Anaphase B Model Equations
1. dS/dt 2 (vsliding - vdep) 2. dL/dt 2
(vpoly - vsliding) 3. µ(dS/dt) / 2 kNLFm(1
- vsliding / Vm)
(Gul Civelekoglu-Scholey)
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Model Results
Conclude Anaphase B kinesin-5 motors drive
ipMT sliding and flux on/off switch
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MT Flux, Sliding and Pacman
sliding KLP61F flux KLP10A
Metaphase
sliding KLP61F flux KLP10A pacman KLP59C
Dynein
Anaphase A
sliding KLP61F flux turned off
Anaphase B
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Mechanism of Anaphase A
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Mechanism of Anaphase A.
Kinetochore motility - Pacman versus poleward
flux.
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Coupled kinesin-13 dependent flux-pacman model
for anaphase A. (Rogers et al, 2004, Nature
427, 364.)
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Cytokinesis in Animal Cells.