Figure 1: Feather vane shapes vary with differential BGZ topology and barb-rachis angles.

(a) Schematic drawing of feather before and after maturation. The barb-rachis angle is a combination of the helical growth angle (θ) during branching morphogenesis and the expansion angle (β) after maturation. (b) Comparing morphologies of two types of chicken remiges with different asymmetry levels and two types of body plumes with different vane widths before and after maturation. Feather epithelial cylinder (before maturation) was cut open at the rachis side and SHH in situ hybridization was used to highlight vanes. Boxes indicate the regions magnified on the right. Vane widths and barb-rachis angles are highlighted by bars and angle symbols, respectively. Scale bars, 500 μm. (c) Quantification of the ratio of different feather epithelial regions before maturation (n=4); vane widths, barb-rachis angles and barb lengths after maturation (n=30). Error bars denote s.d. **P<0.01. (d) Emarginated primary remiges demonstrate abrupt change of vane width. Feathers growing to a point ∼1 cm distal to the emarginated notch position were collected and compared with those ∼1 cm proximal to the notch. A significant shrinkage of the BGZ was observed in those proximal to the notch. Scale bars, 500 μm. (e) Comparisons of vane widths (n=10), barb-rachis angles (n=16) and barb lengths (n=16) at positions ∼1 cm distal and proximal to the notch in mature feathers. Error bars denote s.d. **P<0.01.