Fig. 3. Dorsal-midline stripe of SMAD responses expands and intensifies during early gastrulation. (A-F) Confocal projections of wild-type (WT) embryos stained for Medea (A,C,E), or PMAD (B,D,F). (B-G) Dorsal views or slightly rotated. (A,H) Side views, or slightly rotated. (A,B) Strong nuclear SMAD accumulation was co-incident with initial cellular changes in the cephalic furrow. (C-F) Levels of nuclear staining for both antigens intensified during gastrulation and early germband extension, and the midline stripe widened. (E,F) Response levels dropped dramatically over 2-3 cells at the edges of the stripe. (G) Medea nuclear localization was lost in an embryo lacking WT Mad (M-Z-Mad), and induced globally in embryos expressing constitutively activated TKV under the control of nos>Gal4 (H). Note that somatic cells stain more intensely than posterior germ cell primordia, and that this embryo is at stage 5. Anterior is leftwards.