November 12, 2004
La Jolla, CA – A Salk Institute research team has discovered how nature controls the degree of binocular vision in mammals, work that could have crucial implications for human stem-cell medicine.
Binocular vision is possible because some nerve cells (neurons) from the retina grow into the same side of the brain during embryonic development while others cross over into the opposite side of the brain. A research group at the Salk, led by Dr. Dennis O’Leary, has now discovered that the proportion of neurons that cross over is determined by a single regulatory protein called Islet-2. The startling results were published in the journal Cell today.
Binocular vision is essential to all predatory animals, including humans, because it provides us with depth perception. Prey animals, such as many birds, have sideways-projecting eyes and virtually no binocular vision.
O’Leary’s group determined that Islet-2, a protein that turns on or off other genes that control the connections between nerve cells, has a very specific role in controlling the degree of binocular vision. It suppresses two key chemical signals called Zic2 and EphB1 that ensure retinal neurons grow ipsilaterally, that is, into the same side of the brain. In genetically engineered mice without the gene for Islet-2, Zic2 and EphB1 are able to exert their effects unchallenged and a greater percentage of retinal cells connect to the same side of the brain.
Thus, using this ‘genetic reostat’ nature appears to be able to ‘dial up or down’ the degree of binocular vision required in the developing animal simply by controlling the amount of Islet-2 produced by the retina.
Dr. O’Leary’s fascinating discovery may have crucial implications for stem-cell medicine for repairing damaged nerves. “If you’re going to use stem cells for therapy,” O’Leary said, “you need to know what genes are involved in determining and restricting their fate.”
The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. Jonas Salk, M.D., founded the institute in 1960 with a gift of land from the City of San Diego and the financial support of the March of Dimes.