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RE: Feather Symmetry from Asymmetry Through Wnt3a Gradient

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Jaime A. Headden
>   Yue Y.-c., Jiang T.-x., R. B. Widelitz, and Chuong C.-m. 2006.
>    Wnt3a gradient converts radial to bilateral feather symmetry
>    via topological arrangement of epithelia. _Proceedings of the
>    National Academy of Sciences, Philadelphia_ 103(4):951-955.
> Abstract:
>   "The evolution of bilaterally symmetric feathers is a
>    fundamental process leading toward flight. One major unsolved
>    mystery is how the feathers of a single bird can form radially
>    symmetric downy feathers and bilaterally symmetric flight
>    feathers. In developing downy feather follicles, barb ridges
>    are organized parallel to the long axis of the feather
>    follicle. In developing flight-feather follicles, the barb
>    ridges are organized helically toward the anterior region,
>    leading to the fusion and creation of a rachis. Here we
>    discover an anterior--posterior molecular gradient of wingless
>    int (Wnt3)a in flight but not downy feathers. Global inhibition
>    of the Wnt gradient transforms bilaterally symmetric feathers
>    into radially symmetric feathers. Production of an ectopic
>    local Wnt3a gradient reoriented barb ridges toward the source
>    and created an ectopic rachis. We further show that the
>    orientation of the Wnt3a gradient is dictated by the dermal
>    papilla (DP). Swapping DPs between wing covert and breast downy
>    feathers demonstrates that both feather symmetry and molecular
>    gradients are in accord with the origin of the DP. Thus the
>    fates of feather epidermal cells are not predetermined through
>    some molecular codes but can be modulated. Together, our data
>    suggest feathers are shaped by a DP -> Wnt gradient -> helical
>    barb ridge organization -> creation of rachis -> bilateral
>    symmetry sequence. We speculate diverse feather forms can be
>    achieved by adjusting the orientation and slope of molecular
>    gradients, which then shape the topological arrangements of
>    feather epithelia, thus linking molecular activities to organ
>    forms and novel functions."

Clearly this cannot be correct. After all, the BANDits have shown us that 
feathers actually evolved from flat plate-like scales that
became subdivided. Amazing that these EvoDevo workers can change feathers into 
collagen fibres. :-]

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796