USC scientists uncover secrets of feather...( f noggin for instance they found that...)

f noggin, for instance, they found that the rachis began to split into several small, thin rachides, and the barbs increased in number. When they increased the expression of BMP4, with which noggin interacts antagonistically, they found that the feather's rachis became gigantic and its barbs merged and were reduced in numbers. In this way, they were able to essentially manipulate the number and size of the feather's barbs and rachides.

Finally, when they suppressed Shh, they found a residual webby membrane between the normally separated barbs. "The cells there were supposed to go through apoptosis, or cell death," says Chuong, "in order to create the space between the barbs. But when we took away the sonic hedgehog signal, cell death no longer occurred. It is a similar process to that which occurs in the web of duck feet."

What can these new findings on the morphogenesis of feathers tell us about their evolution? "These results suggest that the barbs form first and later fuse to form a rachis, much like downy feathers are formed before flight feathers when a chicken grows up. Under the general rule of ontogeny repeating phylogeny, downy feather made only of barbs probably appeared before the evolution of feathers with rachides and capable of flight," Chuong says. "However, pinning down the exact moment at which dinosaur scales become chicken feathers is non-realistic. Just like Rome, feathers are not made in one process. It took 50 million years for Nature to refine the process, to transform a scale into a flight machine. There were many, many intermediate stages.

"While Darwin's theory has explained the 'why' of evolution, much of the 'how' remains to be learned," Chuong adds. "Evo-Devo research promises a new level of understanding."

These findings also have medical applications, notes Chuong. "With this study, we learned more about how nature guides epithelial stem cells to form different organs. For example, BMP, Shh and noggin
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Contact: Jon Weiner
jonweine@usc.edu
323-442-2830
University of Southern California
30-Oct-2002

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