Contribution of cell-specific mechanisms to rosette formation. (A) Dynamics of F-actin (lifeact) localization during endoderm internalization. (Top left) Three-dimensional (3D) projection still images, ventral views; arrows indicate the direction of covering. (Bottom left) The x-z projection along the dashed white line (frame at 5 minutes). Note that actin-rich structures on Ea were part of the covering cells (outlined with thin dashed lines). (B) Ventral views onto Ea/Ep; arrows indicate a filopodium that established a lateral contact (dashed line) between neighboring extensions, followed by sealing. (C) Blebbing in P4; arrows point to blebs formed at the anterior side. The boxed area (5 seconds) is shown enlarged on the bottom of the frame as a two-dimensional (2D) confocal image to illustrate separation of plasma membrane and cortex. (D) Blebbing led to anterior translocation. A blebbing event during late stages of Ep covering is shown, with 2D confocal side views, initial anterior position of P4, maximal position after blebbing, and final position after repair of the cortex. (E) Correlation of cross-sectional bleb area and anterior translocation of P4 from three wild-type embryos. A linear regression is shown as a dashed line. (F) Cellular history of the P4 'actin brush' (representations as in (A)). White arrows mark the actin brush. Time is developmental time from fertilization.