Figure 7. Unique expression patterns of Shh in the basal forebrain of avian species.

(A) In the region of the anterior and (B) posterior part of the chick forebrain (labeled “a fb” and “p fb” respectively) Shh expression is restricted to the midline of the basal part of the neural tube. The prechordal mesoderm (pm) also expresses Shh. (C) In the mid-brain Shh is expressed in the chick floor plate (fp) and notochord (nc). (D) In the anterior region of the duck forebrain, the Shh expression is wider than in the chick and encompasses nearly the entire ventral portion of the brain. (E) Similarly, in the posterior region of the duck forebrain, the Shh domain extends more laterally than in the chick. (F) In the floorplate of the duck midbrain, the Shh domain remains wider than in the chick, but this is less dramatic compared to the changes in the forebrain. Scale bar = 100μm.