Origin of Feathers: Feather Beta (ß) Keratins Are Expressed in Discrete Epidermal Cell Populations of Embryonic Scutate Scales
ROGER H. SAWYER,1 BRIAN A. SALVATORE,2 TA-TANISHA F. POTYLICKI,2 JEFFERY 0. FRENCH,3 TRAVIS C. GLENN 4,5 AND LOREN W. KNAPP3
1Department
of Biological Sciences, University of South Carolina, Columbia, South
Carolina 29208
2Department of Chemistry and Biochemistry, University of South
Carolina, Colitinb'a, South Carolina 29208
3Department of Biological Sciences, University of South
Carolina, Columbia, South Carolina 29208
4Savannah R'ver Ecology Laboratory, Aiken, South Carolina
29208
5Department of Biological Sciences, University of South
Carolina, Columbia, South Carolina 29208
ABSTRACT
The feathers of birds develop from embryonic epidermal
lineages that differentiate during outgrowth of the feather germ.
Independent cell populations also form an embryonic epidermis on scutate
scales, which consists of peridermal layers, a subperiderm, and an
alpha stratum. Using an antiserum (anti-FßK) developed to react
specifically with the beta (ß) keratins of feathers, we find
that the feather-type ß keratins are expressed in the subperiderm
cells of embryonic scutate scales, as well as the barb ridge lineages
of the feather. However, unlike the subperiderm of scales, which is
lost at hatching, the cells of barb ridges, in conjunction with adjacent
cell populations, give rise to the structural elements of the feather.
The observation that an embryonic epidermis, consisting of peridermal
and subperidermal layers, also characterizes alligator scales (Thompson,
2001. J Anat 198:265-282) suggests that the epidermal populations
of the scales and feathers of avian embryos are homologous with those
forming the embryonic epidermis of alligators. While the embryonic
epidermal populations of archosaurian scales are discarded at hatching,
those of the feather germ differentiate into the periderm, sheath,
barb ridges, axial plates, barbules, and marginal plates of the embryonic
feather filament. We propose that the development of the embryonic
feather filament provides a model for the evolution of the first protofeather.
Furthermore, we hypothesize that invagination of the epidermal lineages
of the feather filament, namely the barb ridges, initiated the formation
of the follicle, which then allowed continuous renewal of the feather
epidermal lineages, and the evolution of diverse feather forms.
SREL Reprint #2649
Sawyer, R. H., B. A. Salvatore, T. F. Potylicki, J. O. French, T. C. Glenn and L. W. Knapp. 2003. Origin of feathers: Feather beta (ß) keratins are expressed in discrete epidermal cell populations of embryonic scutate scales. Journal of Experimental Zoology 295B:12-24.
