Fig. 11: Rate of EVL edge straightening correlates negatively with the strength of the bond angle constraint as applied to leading edge bond transformations.

a–f Change in several metrics over the course of epiboly with variation in the strength (λ) of the bond angle constraint applied to the transformation of leading edge bonds. (For bonds internal to the EVL, λ is not modified.) The plot for each λ value represents median values of multiple replicates, and the associated 5–95 percentile range, plotted against epiboly progress (the leading edge position over time). Without cell division in b, d (gray box), N = 32 replicates per treatment; with cell division in a, c, e, f, N = 56 replicates per treatment. Vertical lines in a, c, e, f mark the cessation of cell division at 55% epiboly (polar angle ϕ ≅ 0.53π). Legend in b applies to all six plots. Straightness index, with cell division (a) and without cell division (b). The rate of increase of SI over the course of epiboly correlates negatively with λ. (The initial decrease in SI that occurs in most of the treatments in (a) likely is partly due to cell division at the margin, but not entirely: the same decrease occurs when cell division is disabled (b), though only at higher values of λ.) Margin cell count, with cell division (c) and without cell division (d). The model allows cells both to enter and to leave the margin; the change in cell count over time is therefore the net change. Note that despite differences in the time course of margin cell population decrease, all treatments result in a similar net loss of ~60 margin cells by the end of epiboly. The initial net increase in margin cell count that occurs in most of the treatments in (c) is due entirely to cell division during early epiboly, since no such increase occurs when cell division is omitted from the model (d). e Cumulative margin cell rearrangement events. The total number of events correlates negatively with λ. f Tension along the leading edge. The rate of increase in tension correlates negatively with λ. g Selected time points in a single simulation run with λ = 10. Straightening is delayed until much later in epiboly. See also Supplementary Movie 15. Vegetal pole is located at the bottom in lateral view (63% epiboly) and marked by a white dot otherwise (96%, 99%).