Nav: Home

Researchers Solve A Puzzle In Eye Development

January 27, 1997

St. Louis, Jan. 27, 1997 -- Researchers at Washington University School of Medicine in St. Louis have solved a centuries-old puzzle: Do both our eyes develop from a single precursor or does each eye develop from a separate structure?

"This question arose long ago because some infants are born with a single, Cyclops-like eye," says Yi Rao, Ph.D., assistant professor of anatomy and neurobiology. "Our work shows that the embryo has a single eye field that normally separates into two. If this fails to happen, cyclopia occurs."

The findings are published in the Feb. 1 issue of Development. Rao's graduate student, Hua-shun Li, is lead author. Jane Y. Wu, Ph.D., assistant professor of pediatrics and molecular biology & pharmacology, is a collaborator.

Most cyclopic humans die before or shortly after birth, but their existence in reality as well as myth sparked a debate about whether two normal eyes fuse or a single eye fails to split into two. "It was not until the beginning of this century that embryologists began to subject this problem to experimental tests," Rao says.

Rao realized he could explore eye development after he discovered a gene he named ET, which is expressed early in embryonic development. The gene produces a protein belonging to a new family of transcription factors called T domain proteins, which bind to other genes and turn them on. "Most likely ET controls eye formation," Rao says.

This molecular marker made it possible to locate the part of the embryo that develops eyes. By tracking the gene's product, the researchers were able to see the eye field of frogs change from a band into two spots over the course of a few hours.

The researchers obtained the same result when they repeated the study with another gene, Pax-6, which is known to regulate eye development in vertebrates and invertebrates.

They also asked why two eye spots form. "We found that an inhibitory signal shuts off ET expression in the middle of the eye field," Rao says.

The signal came from the prechordal mesoderm, which lies beneath the center of the eye field. When the researchers removed this tissue, the eye field formed, but it did not divide into two, so the resulting tadpole was cyclopic. Similar experiments showed that the same mechanism operates in chick embryos.

Two recent discoveries suggest the mesodermal signal could be made by a gene called sonic hedgehog, which is expressed in prechordal mesoderm and is known to regulate nervous system development. In 1996, collaborators in Bethesda and Baltimore found that mice without this gene develop cyclopia. The same year, researchers in Toronto, St. Louis and Philadelphia identified a mutation in the sonic hedgehog gene as the cause of a birth defect called holoprosencephaly, in which the forebrain fails to cleave into two hemispheres. This condition occurs in 1 in 250 miscarried fetuses and 1 in 16,000 live births. Cyclopia accompanies severe holoprosencephaly.

The work with humans and mice and the current study with frogs and chicks suggest that the interaction between the eye field and sonic hedgehog may be a general phenomenon. "We think it may apply to all vertebrates," says Rao.
-end-
Images of the frog embryo are available.

Li H, Tierney C, Wen L, Wu JY, Rao Y. A single morphogenetic field gives rise to two retina primordia under the influence of the prechordal plate. Development. 1997;124(3); 603-615.

Washington University School of Medicine

Related Eye Articles:

Antibody-based eye drops show promise for treating dry eye disease
Researchers have identified the presence of a specific type of antibody, called anti-citrullinated protein autoantibodies, or ACPAs, in human tear fluid.
Left eye? Right eye? American robins have preference when looking at decoy eggs
Just as humans are usually left- or right-handed, other species sometimes prefer one appendage, or eye, over the other.
The algae's third eye
Scientists at the Universities of W├╝rzburg and Bielefeld in Germany have discovered an unusual new light sensor in green algae.
Making an eye for you
Kyoto University scientists utilize simulations and laboratory experiments to find that cells sense the mechanical forces to form the primordial eye, the optic cup.
A trained eye
UCSB researchers show that category learning can be influenced by where an object is in our field of vision.
Decrease in eye injuries to children
Eye injuries that sent children to emergency departments in the United States decreased from 2006 to 2014, and most eye injuries posed low risk for vision loss.
Increased electrical activity in eye may relieve short-term dry eye pain
A boost of electrical activity in the eye's mucous membranes may lead to new treatments for the painful condition known as dry eye.
An eye toward regeneration
UNLV scientist Kelly Tseng, Ph.D. and her team have found that frog embryos can fully regrow their eyes after injuries, a breakthrough that may lead one day to the ability to orchestrate tissue regeneration in humans.
Art is in the eye of the beholder
A researcher from James Cook University in Australia has found that a person's mental state affects how they look at art.
In the eye of the medulloblastoma
Can genes normally expressed only in the eye be activated in brain tumors?
More Eye News and Eye Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.