Feather Arrays Are Patterned by Interacting Signaling and Cell Density Waves

The study demonstrated that feather patterning in avian skin was governed by a coordinated system involving fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) signaling, along with mesenchymal cell movement, forming a reaction-diffusion-taxis system. This system was mechanochemical, with FGF20 playing a central role in cell aggregation and epidermal compression, enhancing FGF20 expression. Feather formation was driven by a wave of Ectodysplasin A (EDA) expression, which spread across a mesenchymal cell density gradient, facilitating pattern formation. In flightless birds like emus and ostriches, this patterning was disrupted, with ostriches forming feather primordia without a wave, similar to mammalian hair follicle formation, and emus lacking sufficient cells for initial tract formation. The research highlighted the importance of the EDA/EDAR pathway in ordered pattern formation in flighted birds.