Figure 1.

Dpp-dependent regulation of zen expression. Cross sections of embryos hybridized with zen antisense RNA probes. Dorsal is up. (A–D) Wild type, (E,F) dpp^hr4/dpp^hr4, (G,H) dpp^hr27/dpp^hr27, (I,J) dpp^H94/dpp^H94, (K,L) sogYS06/Y. (A) Embryo in early to mid-cellularization showing the broad dorsal-on/ventral-off zen pattern. (B) Embryo in mid-cellularization undergoing zen refinement. (C) Embryo in mid- to late cellularization showing the refined zen pattern restricted to the presumptive amnioserosa. (D) Embryo undergoing gastrulation with continued strong zen expression. Remaining embryos on the left are in mid- to late cellularization and can be compared with (C), and those on the right are beginning gastrulation and can be compared with (D). Note the decrease in the level of zen transcripts during mid- to late cellularization with decreasing dpp activity, and the loss of expression by gastrulation. Although a reduction in the level of transcripts was observed in dpp^hr27 embryos, the ventral limit of zen expression did not change significantly. In the absence of sog, zen expression is maintained to gastrulation, but there is no refinement.