Researchers have found that a protein critical to the embryonic development of limbs also plays a role in determining how the mammalian neocortex, the outer layer of the brain, is formed. "We knew that signaling proteins associated with patterning other parts of the body [were] found in the embryo cortex, but we did not have an easy way to find out what they were doing there," neurobiologist Elizabeth Grove of the University of Chicago says. "There has been some speculation that cortical patterning depended on completely unique mechanisms."

The brains uppermost layer is carefully laid out, with specific areas dedicated to controlling the movement of body parts and receiving sensations from eyes, ears and skin. How this pattern becomes established during development is poorly understood. Now Grove and a colleague, reporting in todays Science, have found that Fibroblast Growth Factor 8 (FGF8), whose absence prevents limbs from growing normally, acts as a signal telling the neocortex which way is front.

When the FGF8 gene was injected into or removed from the front part of the brains of embryonic mice, structures toward the front became elongated or foreshortened, respectively. And when FGF8 was injected into the rear of the brain, a second set of whisker barrelsgroups of cells found toward the front of the brain that monitor whats happening to the whiskersshowed up toward the back.

This result may shed light on the mechanisms behind the evolution of the brain, which often involves tacking new areas onto the cortex. "We have had no idea how evolution achieved this kind of change," Grove notes. "So it is exciting to find that you can add a new area by modifying signaling by a single protein."