Fig. 1

Cortical granules in the mouse egg. a Confocal cross-sections of z-projections of individual and merged channels of ovastacin^mCherry eggs (red) fixed and stained with LCA-FITC (green). Arrows, cortical granule free zone. Scale bar, 20 μm. b XZ projection of XY optical sections (0.2 μm) of zona-free ovastacin^mCherry eggs stimulated to exocytose cortical granules (red). Microvillar plasma membrane (green), actin (gray). Scale bar, 5 μm. c A XY optical section of transgenic eggs sampled every 5 s (×50). Enlarged views (right) at indicated time points. C1, a stationary cortical granule (red, arrow) and a cortical granule (red, arrowhead) captured and pulled by retracting F-actin (gray, dashed yellow line). Plasma membrane (green) accumulates in a reservoir (dashed white line). C2, a cortical granule (red, arrowhead) moving along an actin structure (gray, dashed yellow line) Scale bars, 5 μm (left), 2 μm (right). See corresponding Supplementary Movies 1,2. d Quantification of cortical granules in (+; n = 415) and not in (-; n = 734) contact with actin. **p < 0.01 by two-tailed Student’s t-test. Error bar = s.e.m. The experiment reflects 3 biologically independent replicates. e Zona-free ovastacin^mCherry eggs were fixed 15 min after stimulation with SrCl₂ and immunostained with phalloidin. iSIM projection of egg cortex with a magnified view (inset) showing single cortical granules (red, white arrows) juxtaposed with actin structures (gray). f Profile of dashed line in e (inset) indicating peaks in mCherry (CG, cortical granule) and phalloidin (actin) channels. g XZ projection spanning 8 μm. Volumes were acquired every 10 s at 0.2 μm steps for 5 min with iSIM. A representative iSIM image of an XZ projection of an egg with cortical granules (red) and the plasma membrane (green). Enlarged views at indicated time points corresponds to the white inset in the ovastacin^mCherry channel. A cortical granule (circle) approaches the plasma membrane (dashed green line). Scale bar, 5 μm. See corresponding Supplementary Movie 3. h First frame from iSIM time-lapse series in g with overlaid vesicle tracks in the cytoplasm (bottom) and cortex (top). Lines are colored to indicate time (lower left). i Histogram comparing distribution of cortical granules in the cytoplasm (n = 311) and cortex (n = 3710) during 5-min live-imaging period. Source data are provided as a Source Data file