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Nature
2002[Nov]; 420
(6913
): 308-12
PMID12442169
show ga
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.
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