Figure 2

Nuclear density patterns and movements in living Histone2A-GFP embryos. (a,b) Cylindrical projections of average nuclear density maps derived from portions of 22 living embryos expressing Histone2A-GFP. Density maps for this set of embryos are shown at the start of stage 5 (a) and at the end of stage 5 (b). The axis and isodensity contours are labeled as in Figure 1. The density patterns seen are remarkably similar to those derived from fixed material (Figure 1). (c) Orthographic projections of the average distance and direction of nuclear movement in two dimensions for n = 1 embryo in the dorsal orientation, n = 8 embryos in the lateral orientation, and n = 4 embryos in the ventral orientation. These arrows represent a local average movement within each embryo calculated from time-lapse series as well as an averaging over the various embryos in similar orientations. As expected from the changes in nuclear densities, a net flow of nuclei from the poles towards the mid-dorsal region was observed.