FIGURE 4. The role of Shh in barb formation.

a, Normal feather whole-mount in situ hybridization of Shh and BMP2. b, Shh inhibition by RCAS–antisense Shh or cyclopamine produces fused vanes. c, Diagram showing changes in b. Barbs are red and barbules are green. d, Cross-sections (stained with haematoxylin and eosin) show barb ridge segments that fail to separate, varying from more severe (bottom left quarter of cross-section) to less severe (top right segment). e, Greater magnification of boxed section in d. f, g, Apoptosis in late-differentiated barb ridges in normal and Shh-suppressed follicles. bp, barbule plate; fs, feather sheath; mp, marginal plate; pe, pulp epithelium. Scale bar, 100 m.