Chicken embryonic E16 scutate scale and feather samples

Feather evolution enabled feathered dinosaurs and early Mesozoic birds to venture into new ecological niches. Studying how feathers and scales are specified provides insight into how a new organ evolves. We use genome-wide analyses to identify feather-associated genes and test their feather-forming ability by expressing them in chicken and alligator scales. Intermediate morphotypes revealed five cardinal morphogenetic events: localized growth zone, follicle invagination, branching, feather keratin differentiation and dermal papilla formation. In contrast to molecules known to induce feathers on scales (retinoic acid, beta-catenin), we identify novel scale-feather converters (Sox2, Zic1, Grem1, Spry2, Sox18) which induce only one or several of the five regulatory modules. Some morphotypes resemble filamentous appendages found in feathered dinosaur fossils, while others demonstrate some characteristics of modern feathers. We propose that at least five morpho-regulatory modules were used to diversify ancient reptile scales. The regulatory combination and hierarchical integration led to extant feather forms. Scale samples treated with gene misexpression or retinoic acid were collected at E16. RNA-seq was performed to study the gene expression profiles of the treated samples, compared to the GFP control and normal feather samples. There are 2-3 replicates for each sample group.