Asymmetry in the frequency and position of mitosis in the mouse embryo epiblast at gastrulation

A

Confocal imaging of a transverse section at PS level from an E6.5 embryo labelled for mitosis (Phh3, magenta) and F‐actin (Phalloidin, grey). The apical cell attachment of non‐apical Phh3‐positive cells is highlighted in the zoom. Arrowheads show non‐apical mitoses. Scale bar: 20 μm.

B

Zoom from confocal imaging of a section of E6.25 embryos showing mitoses (Phh3, magenta) occurring with a parallel (left) or a perpendicular (right) axis at the apical pole. Scale bar: 30 μm. Blue dotted lines show parallel axes of division (left), while yellow dotted line shows a perpendicular axis of division (right), relative to the epithelium.

C–E

Proportion of mitosis and non‐apical mitosis is stable through time at the PS: Graphs representing (C) Mitotic Index (Phh3 over DAPI) at the PS of E6.5, E6.75 and E7 embryos. (D) Proportion of non‐apical mitosis (non‐apical Phh3 over DAPI, in percentage), and (E) ratio of non‐apical mitosis (non‐apical Phh3 over total Phh3, normalized by the number of nuclei, in percentage). Data information: values are shown as Mean ± SEM. E6.5: n = 18 slices from six embryos, E6.75: n = 11 slices from five embryos, E7: n = 18 slices from four embryos. Normality was assessed using a Shapiro–Wilk test followed by either an ANOVA test (C) or a Kruskal–Wallis test (D, E). ns, non‐significant.

Figure EV3. Non‐apical division at the PS .