Figure 4.

Disrupting CCT eliminates differential blastoderm migration and eliminates axis realignment. (A) An asymmetric embryo grown in reduced, 62.5 μM Ca²⁺ media. (i) The initial blastoderm mass defines the AV axis (red arrows). (ii) The location of blastopore closure and eventual AP axis (blue arrows) coincide with the initial AV axis (red arrows). (iii) The migration pattern of the blastoderm shows nearly uniform migration (red parallel lines) over the course of epiboly. Consequently, migration of the center of the blastoderm margin (magenta transverse line) lies very near the AV axis (dashed black line; cf. Fig. 1C). (B) (i and ii) Quantification of the CCT force which is equivalent to the slope of the linear fit. The slope of the linear fit is statistically equivalent to 0 when CCT is disrupted by lowering Ca²⁺ to 62.5 μM (i; E2(−), −4 ± 5 nm s⁻¹, R² – 0.005, p-value = 0.82) or by introducing 13.8 μM blebbistatin (ii; Bleb, 3 ± 5 nm s⁻¹, R² – 0.003, p-value = 0.56). (iii) F_CCT/c_Drag is statistically significantly lower (^∗∗∗p < 0.001) in embryos grown in E2(−) media or with introduced blebbistatin compared to embryos grown in E2(+) media. Error bars represent the standard deviation of the slope of the fit as described in Fig. 3C. (iv) Overall rates of epiboly in E2(+), E2(−), and E2 with 13.8 μM blebbistatin. The overall rate of epiboly in E2(−) is statistically equivalent to that observed in E2(+), whereas introduction of blebbistatin severely delays epiboly. The rates of epiboly reflect the mean ± SD of the average rate of epiboly over multiple embryos (16 for E2(+), 15 for E2(−), and 11 for Bleb). (See also Fig. S6, Movies S4 and S5, and Table S1 for more detailed fit parameters.)