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Clarity in Vision


Researchers peer into the eye to understand how the lens forms from a collection of progenitor cells into a structure unlike any other in the body.
normal lense and lens lacking N-cad

Normal lens development, showing properly stretched cells (left), lens cells lacking N-cadherin become bunched. Image credit: Sue Menko Laboratory, Thomas Jefferson University

The lens of the eye: clear as crystal but made out of layers and layers of cells stretched thin to create a completely transparent lentil-shaped ellipse that sits just behind the pupil. It is a feat of cellular reorganization. How do the cells of a growing embryo create such a complex and unusual form?

Researchers investigating this process at Thomas Jefferson University have found that one anchoring protein is essential for helping the cells hold onto the back of the lens while another anchoring protein stretches the other end toward translucency. Their results were published in the journal Developmental Biology.

The mammalian lens does the job of projecting images of the world onto the cells on the retina along the inside back wall of the eyeball, which then sends those images to the brain for interpretation. During embryonic development the cells that become the lens migrate and stretch, while the organelles that might cloud the picture are taken out of the way. Senior author Sue Menko, PhD, Professor in the Department of Pathology, Anatomy and Cell Biology, together with first author and MD/PhD student Caitlin Logan and colleagues, performed a series of experiments to demonstrate that a cell-to-cell adhesion protein called N-cadherin was responsible for giving these developing cells both an anchor and motile force that drives their stretch.

N-cadherin is a member of a large family of anchoring proteins, best known for its role in cell-to-cell connection in the brain, the heart, as well as its role in cancer. When Dr. Menko and colleagues deleted the N-cadherin protein at a particular moment in lens development, the cells held together but weren’t able to stretch properly. Since lens fiber cells make up the bulk of the lens mass, this defect results in the creation of a tissue that would be unable to provide focus.

The researchers also tested whether a different member of the cadherin family (E-cadherin) could act as a stand-in. “For a while, E-cadherin seems to work. But as the lens developed further E-cadherin wasn’t able to perform all of the functions of N-cadherin,” said Dr. Menko.

Now that they have a better sense of the cellular and molecular interactions that drive normal lens formation, Dr. Menko and her colleagues are looking at how these processes are altered during eye disease and injury. 

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Edyta Zielinska