Supplementary Figure 6: Wnt11/Fz7-signalling within the blastoderm margin spatially restricts blastoderm fluidization.

a, Exemplary confocal images of deep cell-cell contacts (white arrowheads) during mitotic rounding for WT, slb and MZ fz7a/b marginal cells labelled by membrane-RFP pseudo-coloured in green, yellow and magenta, respectively. Nuclei are labelled by H2B-GFP (blue) and interstitial fluid by dextran (cyan). b, Deep cell-cell contact length normalized to cell diameter plotted for the following conditions: 9 min before metaphase (t_bm), at metaphase (t_m) and 9 min after metaphase (t_am) for cycles 11^th to 13^th for WT, slb and MZ fz7a/b marginal deep cells (WT n = 16 contacts; slb n = 12 contacts; MZ fz7a/b n = 15 contacts). Grey dashed lines indicate the metaphase time points for each cell cycle. Cyan shaded box shows the period of contact disassembly and orange shaded box the period of contact re-assembly. c, Bar plot of cell-cell contact length reduction for WT, slb and MZ fz7a/b marginal deep cells (cycle 11: WT n = 14 contacts; slb n = 10 contacts; MZ fz7a/b n = 14 contacts; cycle 12: WT centre n = 14 contacts; slb n = 7 contacts; MZ fz7a/b n = 7 contacts). Contact length reduction (D) is expressed as D = L_bm - L_m; where L_bm, contact length 9 min before metaphase and L_m, contact length at metaphase (data were normalized to L_bm for each cycle). d, Bar plot of cell-cell contact length change for the conditions in (c). Contact length change (R) is expressed as: R = L_am - L_bm; where L_am, contact length 9 min after metaphase and L_bm, contact length at 9 min before metaphase (data were normalized to L_bm for each cycle). e, Bright-field images of exemplary deep cell aspirations in the blastoderm margin of WT and MZ fz7a/b mutant embryos at the onset of doming. Black arrowheads indicate how far the cells have flown into the aspiration pipette. Bar plot on the right shows marginal blastoderm viscosity calculated from the aspiration experiments for WT and MZ fz7a/b mutant embryos at the onset of doming (WT, n = 11 embryos; MZ fz7a/b, n = 13 embryos). f, Exemplary single plane fluorescence/bright-field images of WT embryos containing transplanted WT central, WT marginal and MZ fz7a/b marginal cells in their blastoderm centre. Transplanted cells are fluorescently marked by H2B-GFP pseudo-coloured in red, green and magenta, respectively. g, Exemplary confocal images of donor and host deep cells within the blastoderm centre for the conditions shown in (f). Transplanted donor cells are marked by membrane-GFP (WT centre, red; WT margin, green; MZ fz7a/b margin, magenta), host cells by membrane-RFP (grey), nuclei by H2B-GFP (magenta) and interstitial fluid by dextran (blue). h, BYI displacement as a function of time during doming for the different conditions shown in (f) (WT centre to centre, n = 7 transplants; WT margin to centre, n = 4 transplants; MZ fz7a/b margin to centre, n = 5 transplants). i, Bar plot of the normalized cell-cell contact time in the conditions shown in (f) (WT central cells n = 100; WT marginal cells n = 360; MZ fz7a/b marginal cells n = 200). The onset of doming is indicated by grey dashed line. Images are representative of 3 embryos each (a), at least 5 transplants each (f, g), and 3 (b-e, h) or 5 (i) biological replicates (different embryos in b-d, i; independent embryo batches in e, h). Data are mean ± s.e.m; Kruskal-Wallis test (c, d, i); Two-tailed Mann-Whitney test (e). Scale bars: (a) 20 µm; (e, f) 100 µm; (g) 20 µm.