The Brains Behind the Face

WASHINGTON, D.C.--Beauty ads claim that retinoic acid, better known as vitamin A, removes wrinkles from aging faces. But a new study suggests that it is even more important for very young faces. Retinoic acid helps direct the proper development of both the face and the forebrain, which governs higher thought and reasoning, scientists reported 18 February at the annual meeting of the American Association for the Advancement of Science, ScienceNOW's publisher. The study is the first to implicate a single genetic pathway in the development of both the forebrain and the face, and it may provide insights into some birth defects.

Although doctors have long observed a connection between facial and brain birth defects, researchers didn't think there was a genetic link. Because the brain provides a sort of scaffolding for the facial features, scientists assumed that if something went wrong in brain development, the face would simply lack structural support and become deformed. But the new research suggests that problems with one gene pathway may cause both kinds of defects, says developmental biologist Harold Slavkin of the National Institute of Dental and Craniofacial Research in Bethesda, Maryland.

That pathway involves sonic hedgehog, a versatile developmental gene that controls limb growth and patterning. Previous work by several groups had shown it is also important for early head development. But what controls the gene? In the limbs, retinoic acid will turn sonic hedgehog on and off. To find out if that happens in the face, a team led by developmental biologist Jill Helms of the University of California, San Francisco, applied a molecule that blocks the retinoic acid receptor to the head region of developing chicks. They found that the populations of cells destined to become face and forebrain began to die. The chicks never developed a forebrain, forehead, nose, or eyes and the animals soon died. However, if the researchers later applied extra retinoic acid, or extra doses of sonic hedgehog, the chicks developed nearly normal features.

Helms is "at the forefront" in the effort to sort out the earliest patterning of face and head, Slavkin says. The work may also have practical implications: Proper amounts of vitamin A during key stages of pregnancy might help prevent some birth defects, Helms notes.