Fig. 3. Noggin interferes with Nodal and Pitx2 expression. (A) A Noggin-bead that has almost completely abolished Nodal expression in the LPM. (B) Another example in which Noggin had a partial effect on Nodal expression. (C) When the Noggin bead is applied at stage 7-8 HH, the effect is minimal. (D,E) Blocking of BMP signaling by Noggin in the right LPM, either by using recombinant protein (D) or an aggregate of Noggin-expressing cells (E), has no effect on Nodal expression. The insert in E shows the high level of Noggin expression by the cellular aggregate. (F) Applying Noggin to the left LPM before activation of Pitx2 expression prevents its normal expression. (G,H) Noggin applied after Pitx2 activation of expression represses Pitx2 expression around the bead (G) or in a more ample domain (H), as marked by the arrows. (I) A PBS-loaded bead has no effect on Pitx2 expression. (J) Noggin does not modify Pitx2 expression when applied on the right.