Stem Cells Form Light-Sensitive 3-D Retinal Tissue

When we view a sunset or a soccer game, an intricate, orchestrated series of events takes place in our eyes. Light passes through the front part of each eye and is refracted and focused on the retina, a thin, delicate tissue at the back of our eyes. The retina contains many specialized cells, including photoreceptor cells, which convert light into electrical signals. These signals are then processed and sent to the brain. If the photoreceptor cells malfunction or die, vision loss and blindness can occur.

Researchers have previously shown that induced pluripotent stem (iPS) cells can grow into a type of retinal cell under certain cell culture conditions. These types of stem cells are adult cells that have been genetically reprogrammed to take on the characteristics of embryonic stem cells. They can grow indefinitely in the laboratory and can theoretically change, or differentiate, into all cell types found in the body.

Previous work showed that mouse and human embryonic stem cells can develop into a 3-D optic cup in culture that resembles the embryonic vertebrate eye. A team led by Drs. Xiufeng Zhong and M. Valeria Canto-Soler at Johns Hopkins University set out to determine to what extent iPS cells could be prompted to differentiate and acquire structural and functional features similar to a human retina. The work was funded in part by NIHs National Eye Institute (NEI) and National Heart, Lung, and Blood Institute (NHLBI).

The scientists grew human iPS cells in culture dishes in the lab. They reported online in Nature Communications that they were able to coax the cells to gradually take on the characteristics of retinal cells without adding many of the chemicals typically used to induce the cells to mature.

Over time, the iPS cells spontaneously formed cup-like 3-D structures in a sequence of events that mimicked what occurs during human development. The structures developed layers containing all the major cell types that are normally present in the retina, including photoreceptor cells.

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Stem Cells Form Light-Sensitive 3-D Retinal Tissue