Sbf and Rab35 are required to remodel the apical surface during constriction. (A) Scanning EM images of control, Sbf shRNA, and Rab35 shRNA embryos during ventral furrow formation. Embryos are oriented with anterior left and posterior right. (B) Number of bleb-like structures (minimum 0.16 µm and maximum 1.6 µm in size) in a 45 µm² area imaged by scanning EM. (C) TEM images of the apical surface in control, Sbf shRNA, and Rab35 shRNA embryos. “A” and “B” markings indicate apical and basal portions of the cell, respectively. (D) Quantification of the convolution metric (the measured surface area divided by the linear length) in TEM images. Scale bar in C represents 400 nm. Statistical significance was calculated using a Mann–Whitney U test. *, P < 0.05; **, P < 0.005; ***, P < 0.0005.