A first look at the eye's stem cells.

Neither the mammalian eye nor the brain can repair itself. Still, the brain retains stem cells, precursors capable of proliferating into any of the organ's various cell types (SN: 11/7/98, p. 293). Researchers now find that the eyes of mice also harbor a population of stem cells, raising hope of treating blinding illnesses such as retinitis pigmentosa.

In animals whose eyes can regenerate, such as fish and frogs, stem cells reside in the ciliary margin, an area on the outer edge of the retina near the iris. Brenda K.L. Coles of the University of Toronto and her colleagues have now isolated candidate stem cells from a similar region in adult mice.

Like the cells that make up the retina's back layer, the putative stem cells are black. When grown in the laboratory, however, the cells give rise to both pigmented and unpigmented cells. The latter resemble the nerve cells that make up the retina's light-sensitive layer. These cells even make proteins characteristic of developing nerve cells.

To determine why mammalian eyes don't regenerate, Coles and her colleagues plan to study what inhibits growth of the newfound cells. They also will inject the cells into mouse eyes damaged by injury or disease to see if the transplants can perform repairs.