The ER in the C. elegans embryo is continuous. (A) Schematics illustrate the photobleached area (orange circles), the measurement regions in the A-P (blue squares) and perpendicular (red squares) directions, and their positions in percent egg length. The solid vertical lines represent the positions of the cleavage plane, determined by referring to the last frame of the video when the embryo has divided. The dotted vertical lines indicate the middle positions of the A-P axis of the embryo. (B) Confocal images of the FLIP experiments (left) and quantification (right) of a representative embryo for the GFP::KDEL photobleached in the anterior or the posterior domain. Gray bars indicate the prebleached first images; black bars indicate repeated bleaching in the remainder of the indicated cell cycle. The graphs for each embryo shown represent the kinetics of fluorescence loss for the corresponding embryo. The black arrowheads indicate NEBD; the white arrowheads indicate cytokinesis; gray shaded areas show the period of isotropic diffusion; asterisks show the anisotropy onset. Also see Videos 1 and 2. Bars, 10 µm. (C) Graphs of the kinetics of fluorescence loss of GFP::KDEL embryos with the alignment to the time point of anisotropy onset. Asterisks show the anisotropy onset. n_anterior = 15; n_posterior = 14. Mean ± SD.