Fig. 1. Measurement of cortex thickness using magnetic beads.
(A) Bright-field (left) and fluorescence (right) images of a dendritic cell expressing LifeAct-GFP (green) and stained with Hoechst (blue), with internalized magnetic beads aligned by a magnetic field. The cortex is pinched between bead 1 (inside the cell) and 2 (outside). Scale bar, 5 μm. (B) TEM of the cortex of a cell pinched between two magnetic beads. Scale bars, 2 μm (black, top) and 500 nm (white, bottom). (C) Distances between bead surfaces for pinching in control cells (blue, n = 67 cells, N = 10 independent experiments), pair of beads observed outside (gray, n = 69, N = 2) and inside (green, n = 20, N = 13), and pinching in cells treated with 500 nM LatA (purple, n = 26, N = 5). Each point is the median of a 5- to 15-min measurement at 1.25 Hz on a single cell. (D) Average force-indentation curves for bare beads (black, nc = 49 compressions, n = 16 bead pairs), serum-coated beads outside of cells (beige, nc = 143, n = 11), beads pinching the cortex of control cells (blue, nc = 234, n = 20 cells, N = 5), and 500 nM LatA–treated cells (LatA, purple, nc = 85, n = 7, N = 1), obtained from increasing the magnetic field from 5 mT (70 pN) to 50 mT (~1000 pN) in 1 s and decreasing it back.