Cell Mechanics of Cell Division

Simultaneous tracking of the position of the spindle poles and cortical myosin distribution. (a) Software for particle tracking was used to locate the position of the spindle poles. (b) Graph of the horizontal displacement of the spindle poles. Time t=0 is the onset of anaphase B at which time the spindle poles start to move away from one another. (c) Vertical displacement of spindle poles. Periodic oscillatory behavior was observed at times -1000 through -500 sec.  (d) Active contours that adapt to the cell boundary were used to monitor the intensity of MRLC along the cell’s cortex. (e) Kymograph of myosin concentration as a function of angle and time (bright = higher intensity). Myosin starts to assemble in a contractile ring corresponding to two bight bands during anaphase. The image shows the same cell as in (b) and (c). The dark regions are blebs that develop during cytokinesis as the cortex of the cell weakens along the flanking regions.

Fluorescence microscopy and DIC images showing the effect of mechanical perturbations of Hela cells expressing MRLC-GFP. The images show a cell proceeding through anaphase and cytokinesis. A bead is attached to cell’s membrane. (a) and (b) show a cell prior without external force. (c) and (d) show the effect of an oscillatory force on the bead: the pole moved towards the bead. In (e) and (f) no external force applied and the pole returns to a symmetric position. In (g) and (h), i.e. during cytokinesis an external force has no observable effect.