Expression of segment polarity genes in embryos. (a) Ventral view of an embryo from the BE stock (including both BE and WT embryos) at 12% DT; en is expressed in the posterior compartment of each segment, which shows that the establishment of its expression is not affected. (b) Ventral view of a WT and a BE embryo at 15% DT; En protein is also detected in some anterior cells of the segments (arrow) in BE embryos. (c) At 25% DT, BE embryos appear shorter than WT, with En present in the anterior and posterior cells of each segment (arrows indicate segment borders). (d) Lateral view of a WT and a BE embryo at 40% DT. Arrows point to posterior cells of the second abdominal segment, expressing en. In BE embryos, En is also detected in anterior cells of each segment (arrowhead). (e) wg expression in embryos at 25% DT (arrows indicate segment borders). In WT, wg mRNA is detected in a single stripe per segment, while an extra wg stripe is present in each segment in a BE embryo. Segment borders allow a clear assessment of the relative position of en and wg expression stripes. Anterior is to the right; scale bar, 100 μm. Mutant embryos from Spr or Fr stocks show identical patterns of en and wg expression.