The diffusion of ER membrane proteins is anisotropic in the A-P axis. (A) Confocal images of the FLIP experiments showing a representative embryo (left) of GFP::SP12 photobleached in the anterior or the posterior domain (orange circles). The fluorescence loss in both directions is parallel until anisotropy onset (asterisks) at a time point preceding NEBD. Also see Videos 3 and 4. (B) Graphs of the kinetics of fluorescence loss for the combined data of GFP::SP12 embryos with the alignment to the time point of anisotropy onset. Three time points before the anisotropy onset are shown. Asterisks show the anisotropy onset. n_anterior = 15; n_posterior = 26. (C) Confocal images of the FLIP experiments showing a representative embryo of RAMP4::YFP photobleached in the anterior or the posterior domain. Also see Videos 5 and 6. (A and C) Graphs show the kinetics of fluorescence loss over time for the corresponding embryos. Gray bars indicate the prebleached first images; black bars indicate repeated bleaching in the remainder of the indicated cell cycle. The black arrowheads indicate NEBD; the white arrowheads indicate cytokinesis; gray shaded areas show the period of isotropic diffusion; asterisks show the anisotropy onset. Bars, 10 µm. (D) Graphs of the kinetics of fluorescence loss for the combined data of RAMP4::YFP embryos with the alignment to the time point of anisotropy onset. Graphs are as described in B. n_anterior = 25; n_posterior = 20. Mean ± SD.