Overview Cell Structures Cell Migration Cell Division  

Probing Intracellular Force Gradient with Soft Polymers during Cytokinesis

Iwasaki and Wang, unpublished results

We have probed intracellular mechanical forces during cytokinesis by microinjecting non-crosslinked, high molecular weight, linear polyacrylamide (PAA) polymers into NRK epithelial cells. The polymers form tangled aggregates, which move and change shapes in response to the distribution of surrounding forces. A similar approach has been used to detect intracellular forces during cell migration.

Movement of PAA Probes into the Spindle Midzone and Severing during Cytokinesis.

PAA is injected into the equatorial region of a prometaphase NRK cell.  A large aggregate near the chromosomes is initially spherical in shape. However, following chromosomal segregation, it elongates perpendicular to the spindle axis and moves rapidly into the newly formed spindle midzone before the initiation of cortical ingression. The aggregate resumes a spherical shape and remains stationary in the midzone during anaphase, but becomes highly elongated during cytokinesis. It is eventually severed by the ingressing furrow, and dispersed into the two daughter cells as small aggregates. Interestingly, the PAA probe fails to show a dumbbell shape as expected for the bisection by a narrow constricting ring, but becomes highly elongated along the spindle axis, suggesting widespread lateral compressive forces. Total time of recording, 60 minutes.

Poleward Movement of PAA Aggregates from the Equatorial Region during Cytokinesis

Prometaphase NRK cells are injected with a mixture of PAA and rhodamine dextran near the equator but away from the chromosomes. The first cell shows the movement of a large PAA aggregate toward the polar region as the cell enters telophase.  The aggregate is elongated along the direction of migration, parallel to the spindle axis, suggesting a pressure differential along the axial direction. The second cell is injected near the spindle pole, where the PAA aggregare shows similar poleward movement and elongation along the spindle axis.  Total time of recording, 35 minutes and 50 minutes respectively.