Fig. 1.

Torso RTK signaling restricts expression of multiple Dorsal targets at the embryonic termini. (A-T) Lateral view of stage 5 wild-type (A-E), DSor (F-J), tor^Y9 (K-O) and wntD (P-T) mutant embryos, immunostained for Sna (A,F,K,P), Vnd (B,G,L,Q) and Brk (C,H,M,R), or hybridized using digoxigenin-labeled RNA probes for sog (D,I,N,S) and wntD (E,J,O,T). Torso-dependent activity limits the expression of Dl targets at the poles. (A-D) Expression of four Dl targets, Sna, Vnd, Brk and sog, is confined to the trunk region and is excluded from the termini. (F-I) In DSor mutant embryos, where Torso signaling is blocked, expression of these Dl targets expands into terminal regions. (K-N) In tor^Y9 embryos, where Torso is overactive, expression of these Dl targets retracts towards more central locations. (E,J,O) Torso signaling regulates wntD expression. Expression of wntD, normally observed in ventro-terminal positions (E), is lost in DSor mutants (J) and expands in tor^Y9 embryos throughout the ventral region (O). (P-T) The Dl targets Sna, Vnd, Brk, sog and wntD are ectopically expressed at the poles of wntD mutants, where Dl is nuclear owing to the lack of functional WntD (see Fig. 2). Embryos are oriented with anterior to the left and dorsal side upwards. Arrows point to the posterior pole.