Novel Tissue Mechanics-Guided Cellular Flows Enable the Evolution of Feather Follicles

The study investigates the role of cellular flows and tissue mechanics in avian skin development, specifically focusing on feather follicle evolution. It reveals that novel cellular flows initiate chemo-mechanical circuits that guide the morphological transitions necessary for feather bud formation. Initially, stiff dermal condensates protrude from a softened epithelial sheet, activating YAP and causing the epithelial sheet to fold and form a stiff cylindrical wall that invaginates into the skin. This process is crucial for forming tightly packed dermal papillae. The study contrasts this with scale development, where a rigid epithelial sheet restricts dermal cell flows, preventing further topological transformations. A topological transformation model was developed to illustrate how these processes enable the evolution of feather follicles.