Fig. 6

Trophectoderm folding orchestrates the final step the blastocyst to egg cylinder transformation. a Stills from a time lapse movie of Lifeact-GFP blastocyst. ExE tissue (red) folding (white arrows) through apical constriction is followed by spreading (yellow arrows) of the visceral endoderm (VE) (yellow outline) and formation of egg cylinder. Stills without coloured overlay are presented in Supplementary Fig. 10a. b Quantification of ExE apical cell surface area, VE apical cell surface area and VE length through time during blastocyst to egg cylinder transformation from three individual embryos shown in Supplementary Movie 8. Cyan boxes indicate the developmental period, during which ExE cell’s apical constriction precedes VE spreading. VE tissue spreading during egg cylinder formation is owing to cell-shape changes as quantified in Fig. 5b. c Quantification of polar TE/ExE apical cell surface area relative to PE/VE position. d Quantification of PE/VE cell aspect ratio relative to PE/VE position. e Quantification of PE/VE cell aspect ratio relative to polar TE/ExE apical cell surface area. f Quantification of polar TE/ExE cell aspect ratio relative to PE/VE cell aspect ratio. For c–f, Pearson correlation test was used, ****p < 0.0001. g Rose diagram for quantification of long cell axis orientation in distal and proximal VE at the early egg cylinder stage. Kolmogorov–Smirnov test: ****p < 0.0001. Distal VE: n = 153 cells, Proximal VE: n = 75 cells. h Representative examples of control and Y27632 (ROCK inhibitor)-treated embryos. Embryos were recovered at E4.75 and cultured ex vivo for 12 hours. In the absence of actomyosin contractility (Y27632) egg cylinder formation fails due to defective ExE folding (Supplementary Movie 10). i Quantification of blastocyst to egg cylinder transformation efficiency in control, and Y27632 treated embryos. χ² test; ****P < 0.0001. For h and i n = 16 control and 29 Y27632-treated embryos. j Model of blastocyst to egg cylinder transformation as a result of TE morphogenesis. Source data are provided as a Source Data file. Scale bars = 20 µm