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Re: Feathers from Scales

[Reposting - re: administrativa]

In article <199610110023.TAA12653@juliet.ucs.indiana.edu>, guy leahy
<n9435712@henson.cc.wwu.edu> writes

>       The following ref brings some interesting data to the "where did 
>feathers come from" debate.
>       Zou, H., & Niswander, L. (1996).  Requirement for BMP signaling
>       in interdigital apoptosis and scale formation.
>        Science, V. 272, pp. 738-741.
>       The authors were able to experimentally manipulate the leg scales
>on chickens so that they were transformed into feathers, fully consistent
>with the idea that feathers are modified scales.

There is an alternative, and more probable, explanation than to assume
that the scales were converted to feathers in this experiment. It is now
known that in embryonic birds the same cells produce either scale or
feather, feather being the default one. Scale production requires
additional signalling which can be blocked by retinoic acid.  Zou et al
stopped apoptosis in chicken embryo by blocking signal transduction.
They were looking at the structure of the digits and used a very specific
agent which blocks apoptosis only in the interdigital cells (they actually
produced chicken embryos with webbed foot). All chicken embryo cells
carry the same genes, but the expression of individual genes is
controlled by several different mechanisms, including signal
transduction. It appears that the agent Zou et al used blocked the scale
producing  signal to various degrees thus allowing production of
feathers in place of one type of scale.

May I add - this explanation neither supports nor refutes the theory that
feathers are modified scales.

Gautam Majumdar                 gautam@majumdar.demon.co.uk