At 02:52 PM 3/3/99 -0500, Ron Ornstein wrote:<<<<
This was the 4th of his commentaries on the Ostrom symposium, all of them quite welcome and accurate. There are only a couple of points that I would like to clarify
Alan Brush gave an outline of feather evolution......
Brush illustrated his talk with
>slides showing the a developmental process by which a feather develops from
>a hair follicle. This is easier to illustrate than to describe, ...
The correct version of this thought, is not that feathers developed from a hair follicle. The feather follicle gives rise to feathers. But both follicles are epidermal derivatives of a placode and share some characteristics. They differ in the family of keratin proteins that are expressed, and in their geometry. To my mind the similarities are only superficial. I'm sure this was a simple oversight on Ron's part
>In it is a truism that feathers are made of keratin. However, the story
>isn't that simple. The feathers of birds are made only of beta keratin, a
>protein unknown in mammals. The beta keratin in feathers is further
>distinguished from other beta keratins by a deletion.
Actually this is much more complex that it seems. Schwitzer presented a slide that illustrates feather keratin that was based on a diagram in my article in Avian Biology (vol 9, 1993). This point is that the family of feather keratins genes (which produced the main structural proteins in ALL kinds of feathers, beaks, scale and scutes)has undergone some evolution since their origin. The original gene was duplicated several times. Subsequently some members underwent a deletion. So the family contains 2 sets of genes, each of which is duplicated several times and exists in tandem repeats in the genome. The evidence for this comes from sequences work on both the proteins and the genes. We know precisely where the deletion occurred. Both the beta-pleated sheet and the Cys containing proteins of the proteins are conserved. This is functionally important. Anyway, the expresses genes exist in tandem arrays of 15-18 members. These can differ in AA sequence. The entire sets (one for contour feathers, another for down, another for scale, etc) are probably repeats 125-150 times throughout the genome. This arrangement, which is different from other epidermal appendages, is highly conserved and determines properties of the structures such as the nature of the filaments and structural molecular organization of the feathers themselves.
It does bring up a problem, one that was mentioned in the discussion. That is in order to use anti-sera to identify feathers, you need to have very pure antigens. With this relatively large number, it is not an easy task!
It is also important to consider from an evolutionary viewpoint that with the feather keratin genes excepted, the genes that determine the linear nature, ramification, growth and timing of feather exist widely in animals. The regulatory events that lead to feather productions are probably a consequence of common cell functions and cytodifferentation. What emerged from the combination of the feather keratins and follicle was a extremely adaptable system capable of producing great phenotypic variation. All excellent conditions of rapid evolutionary change
Alan H. BrushBrush@uconnvm.uconn.edu
92 High St.
Mystic, CT 06355