The morphogenesis of feathers.
Feathers are highly ordered, hierarchical branched structures that confer birds with the ability of flight. Discoveries of fossilized dinosaurs in China bearing 'feather-like' structures have prompted interest in the origin and evolution of feathers. However, there is uncertainty about whether the irregularly branched integumentary fibres on dinosaurs such as Sinornithosaurus are truly feathers, and whether an integumentary appendage with a major central shaft and notched edges is a non-avian feather or a proto-feather. Here, we use a developmental approach to analyse molecular mechanisms in feather-branching morphogenesis. We have used the replication-competent avian sarcoma retrovirus to deliver exogenous genes to regenerating flight feather follicles of chickens. We show that the antagonistic balance between noggin and bone morphogenetic protein 4 (BMP4) has a critical role in feather branching, with BMP4 promoting rachis formation and barb fusion, and noggin enhancing rachis and barb branching. Furthermore, we show that sonic hedgehog (Shh) is essential for inducing apoptosis of the marginal plate epithelia, which results in spaces between barbs. Our analyses identify the molecular pathways underlying the topological transformation of feathers from cylindrical epithelia to the hierarchical branched structures, and provide insights on the possible developmental mechanisms in the evolution of feather forms.
Yu
Mingke
M
Department of Pathology, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, Los Angeles, California 90033, USA.
Wu
Ping
P
Widelitz
Randall B
RB
Chuong
Cheng-Ming
CM
D000818:Animals; D017209:Apoptosis; D001358:Avian Sarcoma Viruses / Q000235:genetics; D005075:Biological Evolution; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins; D002642:Chick Embryo / Q000196:embryology*; D004848:Epithelium / Q000033:anatomy & histology / Q000196:embryology; D005241:Feathers / Q000033:anatomy & histology / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins; D017403:In Situ Hybridization; D008954:Models, Biological; D009024:Morphogenesis; D010641:Phenotype; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta; D019076:Transgenes / Q000235:genetics; D000099176:Noggin Protein
D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D053823:Hedgehog Proteins; D011506:Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D000099176:Noggin Protein