Fig. 6. Exogenous BMP alters normal gene expression in the midline. (A) A PBS-bead in the left LPM does not perturb normal Lefty1 expression. BMP application, either to the left (B) or right (C) of the LPM represses Lefty1 (delimited by the red arrows). (D,E) Transverse sections through the embryo shown in B at the indicated levels. (F) A PBS-soaked bead in the left LPM does not perturb normal Bra expression. Treatment with BMP either to the left (G) or right (H) dramatically decreases Bra expression in the region facing the bead (delimited by the red arrows). (I,J) Transverse sections through the embryo shown in H at the levels indicated. (K) A PBS-soaked bead in the left LPM does not perturb normal Shh expression. (L,M) Loss of Shh expression in the midline (area between the red arrows) after BMP treatment either to the left (L) or to the right (M). The beads of the embryos in (G,L) were dislodged during hybridization. Red asterisks indicate the bead positions.