Fig. 5. BMP signaling interferes with a functional midline barrier. Ventral views of stained embryos at HH stage 7 (A) or HH stage 8 (B,E-H). (C,D) Transverse sections through the embryos shown (A,B). Plane of sectioning is indicated in the individual panels. Chicken embryos are shown that were implanted with BMP2-expressing cells (A,B,E,G) or control cells (F,H) adjacent to the midline on the left side and stained for Nodal (A), Nodal and Lefty (B), Lefty (E,F), or Shh (G,H). Red arrowheads indicate ectopic expression (A,B) or loss-of expression (E-H). Asterisk marks the implanted cell aggregates.