Fig. 5. Dorsal partitions into nucleus-associated cytoplasmic domains in Drosophila. (A) Photobleaching of the cytoplasm preferentially reduces nuclear Dorsal levels in one nearby nucleus. FLIP of the common cytoplasm results in the preferential reduction of nuclear fluorescence in one associated nucleus, suggesting compartmentalization of the syncitial cytoplasm. Bleach box is shown in red. (B) A dorsal surface view, showing high cytoplasmic levels of Dorsal adhering to nuclear-associated domains. (C) A side confocal view, showing dorsal nuclear domains. (D) A drawing of the domains. (E) A FRAP of both nucleus and cytoplasm on the ventral side at the beginning of mitosis that preferentially bleaches one cytoplasmic domain. Rapid recovery in the 25 and 37.5 second panels shows that Dorsal within the domain can exchange with a mobile pool from elsewhere within the embryo. (F) A false color image of an FLIP of peripheral and deep cytoplasm on the dorsal side (bleach box in white), indicating that Dorsal is partially constrained in its mobility near the plasma membrane surface but is more freely diffusing in the lower, deep cytoplasm. Relative linear intensities are indicated by the color bar at the bottom left. (G) Dorsal is partially constrained in its diffusion to the part of the cytoplasm between the nucleus and the plasma membrane. A 5 second FRAP of nucleus (bleach box in red) transiently reduces fluorescence preferentially in the blue zone. In subsequent images (data not shown), cytoplasmic fluorescence is recovered with delayed kinetics by flow from the deep cytoplasm.