Sonic hedgehog, a gene that plays a crucial rule in the positioning and growth of limbs, fingers and toes, has been confirmed in an unexpected place in the embryos of developing mice the layer of cells that creates the skin.
Named for a video game character, Sonic hedgehog describes both a gene and the protein it produces in the body. Its study is important to increase understanding of human birth defects.
It was thought to be exclusively present in the cell layer that builds bone and muscle, called the mesoderm. But University of Florida Genetics Institute researchers have discovered that Sonic hedgehog is also at work in mice limb buds in what is known as the ectoderm, the cell layer that gives rise to the skin in vertebrates.
Finding Sonic hedgehog in this layer of cells is loosely akin to discovering that yeast has crept from the batter to the frosting, where it has the surprising effect of limiting how much the cake will rise. More literally, instead of causing appendages to grow in mice, Sonic hedgehog seems to act as a failsafe mechanism to prevent additional digits.
"Sonic hedgehog protein determines how your limbs form, and why your pinky is at the bottom of your hand and your thumb is at the top," said Brian D. Harfe, Ph.D., an associate professor of molecular genetics and microbiology at the UF College of Medicine. "But what's been previously published is only part of the picture. We determined that Sonic hedgehog signaling is required in the ectoderm to have normal digit formation. Get rid of it, and an extra digit forms."
In this case, when scientists disrupted Sonic hedgehog signaling in a small region of the limb buds of embryonic mice, an additional digit began to arise in what would be the mouse paw.
The discovery, to appear online in this week's Proceedings of the National Academy of Sciences, suggests that Sonic hedgehog's role in the growth of appendages is far more complex than o
|Contact: John Pastor|
University of Florida