Figure 2: Identifying key molecular regulators of feather vane shapes.

(a) Scatter plots depicting the transcriptomic comparisons between lateral and medial primary remige pulp, dorsal and breast plume pulp, respectively. Among the differentially expressed genes we picked out crucial signalling molecules (red) for further characterization. The linear correlation coefficient (r) is very close to 1, indicating highly similar transcriptome profile between samples. (b) The highlighted genes are clustered in two groups, one associated with narrower vanes and the other associated with wider vanes (L and M are the lateral side and medial side of primary remige; D, dorsal plume; B, breast plume, respectively. Two biological replicates are shown). (c) Candidate genes highlighted by RNA-seq analysis demonstrated differential localization in the pulp of growing feathers with different vane shapes (arrows). KRT75 is highly expressed in the rachis epithelium and hence was used as a marker for position alignment between samples. Scale bars, 500 μm. (d) qPCR for CYP26B1 and CRABP1 in the pulp of primary remiges along the wing (lateral-to-medial: X, IX, VII, V, III, n=3 for each position) demonstrates gradually decreased CYP26B1 expression and increased CRABP1 expression. While dorsal plumes have more strikingly elevated CYP26B1 and downregulated CRABP1 expression compared with the breast plumes (n=3). Error bars denote s.d. **P<0.01, NS, not significant.