New 2nd Article in Experimental Zoology

[Markus Moser <m.moser@lrz.uni-muenchen.de>]

Dear all,

for those who want to see how a feather develops/evolves from a
scale-like integumentary structure, have a look at the Feather animation
Quicktime movies at 
http://fallon.anatomy.wisc.edu/feather.html

The source reference is

JOURNAL OF EXPERIMENTAL ZOOLOGY, 294 (2) :160?176 (15-08-2002)

RAPID COMMUNICATION

Shh-Bmp2 Signaling Module and the Evolutionary Origin and
Diversification of Feathers

MATTHEW P. HARRIS, JOHN F. FALLON & RICHARD O. PRUM

ABSTRACT 
To examine the role of development in the origin of evolutionary
novelties, we
investigated the developmental mechanisms involved in the formation of a
complex morphological
noveltyFbranched feathers. We demonstrate that the anterior-posterior
expression polarity of Sonic
hedgehog (Shh) and Bone morphogenetic protein 2 (Bmp2) in the primordia
of feathers, avian scales,
and alligator scales is conserved and phylogenetically primitive to
archosaurian integumentary
appendages. In feather development, derived patterns of Shh-Bmp2
signaling are associated with the
development of evolutionarily novel feather structures. Longitudinal
Shh-Bmp2 expression domains
in the marginal plate epithelium between barb ridges provide a
prepattern of the barbs and rachis.
Thus, control of Shh-Bmp2 signaling is a fundamental component of the
mechanism determining
feather form (i.e., plumulaceous vs. pennaceous structure). We show that
Shh signaling is necessary
for the formation and proper differentiation of a barb ridge and that it
is mediated by Bmp signaling.
BMP signaling is necessary and sufficient to negatively regulate Shh
expression within forming
feather germs and this epistatic relationship is conserved in scale
morphogenesis. Ectopic SHH and
BMP2 signaling leads to opposing effects on proliferation and
differentiation within the feather
germ, suggesting that the integrative signaling between Shh and Bmp2 is
a means to regulate
controlled growth and differentiation of forming skin appendages. We
conclude that Shh and Bmp
signaling is necessary for the formation of barb ridges in feathers and
that Shh and Bmp2 signaling
constitutes a functionally conserved developmental signaling module in
archosaur epidermal
appendage development. We propose a model in which branched feather form
evolved by repeated,
evolutionary re-utilization of a Shh-Bmp2 signaling module in new
developmental contexts.



Markus Moser
Bayerische Staatssammlung fuer Palaeontologie und Geologie
Richard-Wagner-Str. 10
80333 Muenchen
Germany