Supplemental Material

This article contains the following supporting material:

• Movie 1 - Prefurrow contractility in a compressed sea urchin eggs.
  L. pictus eggs were fertilized, stripped of their fertilization envelopes, and flattened under fluorocarbon oil just before nuclear envelope breakdown. In this sequence, the cell begins to drift out of the frame during furrowing. The red circle denotes the margins of the cells at the beginning of the video sequence. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 1A-D.

• Movie 2 - Blebbistatin blocks prefurrow contractility.
  L. pictus eggs were incubated in the presence of 50 μM blebbistatin prior to flattening under fluorocarbon oil. The red circle denotes the margins of the cells at the beginning of the video sequence. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 1E-H.

• Movie 3 - The global rise in cortical contractility initiates at the metaphase-anaphase transition.
  L. pictus eggs were injected with fluorescent histone and allowed to divide before flattening. Note the ingression of the cell margins occurs just prior to the onset of chromosome segregation. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 2.

• Movie 4 - Anaphase and cytokinesis in a spherical sea urchin imaged with polarization optics.
  The left panel depicts a L. pictus egg undergoing the first mitotic division as observed with a LC-polscope. Each frame in the image stack was converted to color surface projections shown in the right panel, illustrating the loss of spindle birefringence relative to edge birefringence as the cell undergoes anaphase and furrow formation. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 4.

• Movie 5 - The global rise in cortical contractility precedes the shift in spindle birefringence.
  L. pictus eggs were flattened under fluorocarbon oil just before nuclear envelope breakdown, and followed through metaphase and anaphase with a LC-polscope. Each frame in the image stack was converted to color surface projections shown in the right panel, illustrating the loss of spindle birefringence following the ingression of the cell margins. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 5.

• Movie 6 - Changes in cortical contractility in a control egg.
  L. pictus eggs cultured in the presence of 0.1% DMSO were flattened under fluorocarbon oil just before nuclear envelope breakdown, and followed through metaphase and furrow initiation with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 6A.

• Movie 7 - Changes in cortical contractility in a nocodazole egg.
  L. pictus eggs cultured in the presence of 50 μM nocodazole were flattened under fluorocarbon oil just before nuclear envelope breakdown, and followed through metaphase and furrow initiation with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 6B.

• Movie 8 - Changes in cortical contractility in an egg containing supernumerary asters.
  L. pictus eggs were treated with hypertonic seawater after fertilization, and then cultured in normal CAFSW up until just before NEB, at which time they were flattened and followed through mitosis with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 6C.

• Movie 9 - Changes in cortical contractility in an egg injected with Rho-GDI.
  L. pictus eggs were injected with 3 mg/ml Rho-GDI until before NEB, at which time they were flattened and followed through mitosis with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 7A.

• Movie 10 - Changes in cortical contractility in an egg treated with the ROCK inhibitor H-1152.
  L. pictus eggs were incubated in 1 μM H-1552 shortly before NEB, at which time they were flattened and followed through mitosis with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 7B.

• Movie 11 - Changes in cortical contractility in an egg injected with MLCK inhibitory peptide.
  L. pictus eggs were injected with 4 mg/ml MLCK inhibitory peptide shortly before NEB, at which time they were flattened and followed through mitosis with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 7C.

• Movie 12 - Changes in cortical contractility in an egg treated with the MLCK inhibitor ML-7.
  L. pictus eggs were incubated in 50 μM ML-7 shortly before NEB, at which time they were flattened and followed through mitosis with DIC optics. Frames were acquired every 30 seconds and played back at 10 frames/second. Video corresponds to Figure 7D.

• Movie 13 - Precocious mobilization of calcium during metaphase induces a cortical contractile response.
  L. pictus eggs were injected with caged IP3 and Calcium green dextran prior to flattening and imaging with DIC (left) and wide-field fluorescence (right) microscopy. IP₃ was uncaged with a single pulse of UV light shortly after nuclear envelope breakdown. Images were acquired every 10 seconds, and played back at 10 frames/second. Video corresponds to Figure 8.