Study hints how scaly dinosaur legs could
get birdlike feathers
Date: March 15, 2016
Source: University of Utah
Scientists identified two genes that make
some pigeon breeds develop feathered feet known as muffs, while others have
scaled feet. The same or similar genes might explain scaled feet in chickens
and other birds, and provide insight into how some dinosaurs got feathers
before they evolved into birds.
The study found that in pigeons with
feathers on their hindlimbs or feet, a hindlimb-development gene named Pitx1 is
less active than normal, while a forelimb-development gene
named Tbx5 is active in the feet, where it normally is not.
In other words, "pigeons' fancy
feathered feet are partially wings," says biologist Mike Shapiro, senior
author of the study published today by the journal eLife.
In mutant pigeons with foot feathers,
"the hindlimb is clearly recognizable as a leg, but it has taken on more
forelimb characteristics," he says. "It's not a complete
transformation of a leg into a wing. Rather, components of the leg are more
winglike, including feathers and a larger leg bone."
Shapiro and colleagues found that
the Pitx1 and Tbx5 genes themselves are no different in
breeds with and without foot muffs. Instead, they learned that nongene
"regulatory sequences" of DNA near the genes act like switches to
turn down the activity of hindlimb gene Pitx1 and turn up activity of
forelimb gene Tbx5 in the embryos of pigeons with foot feathers.
"Our experiments show that these
switches work differently in birds with feathered feet relative to the ones
with normal, scaled feet," Shapiro says.
The two genes were previously known in
all vertebrate animals, and they are linked to limb and other defects in
people. The new study showed how they "provide a mechanism by which scaled
and feathered skin regions can be controlled," Shapiro says.
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