Fig. 1. BMPs positively regulates Nodal expression. (A) Normal pattern of Nodal expression in a stage 8 embryo. (B) Schematic drawing delineating the experiment of bead placement (red circle) into the stage 7-8 lateral plate mesoderm (LPM). Only the placement on the right is depicted, but for each experiment left and right placements were made. (C) A BMP2-soaked bead induces ectopic expression of Nodal in the right LPM. (D) Detail of ectopic right-side expression of Nodal in another embryo with the same treatment. (E,F) Transverse sections of the embryos shown in C,D, respectively, at the level indicated. (G) A BMP2-soaked bead in the left LPM expands the normal domain of Nodal expression. (H) BMP2 maintains Nodal expression, as indicated by the arrow, when the normal domain of expression has moved posteriorly. Treatment with BMP4 (I) and BMP7 (J) had the same effect as treatment with BMP2. (K,L) Repression of Nodal expression after the application of a BMP2-soaked bead (1 mg/ml, K; 0.1 mg/ml, L) at earlier stages (4-6 HH). (M,N) Shh expression is downregulated (arrows) by BMP2 (1 mg/ml, M; 0.1 mg/ml, N) application at earlier stages (4-6 HH). The red asterisk marks the position of the bead in the sections. The bead of the embryo in I was dislodged during hybridization.