Small blobs of human brain grown in a dish have been coaxed into forming rudimentary eyes, which respond to light by sending signals to the rest of the brain tissue.
The pairs of eye-like structures create tissues similar to those in real eyes, including a round lens, which normally focuses an image, and a retina, the patch of tissue at the back of the eye that senses light. In a way, the brain tissue is 鈥渟eeing鈥� light, says at Heinrich Heine University Dusseldorf in Germany.
The development is helping his team understand inherited causes of eye disease, and in future may allow us to grow artificial retinas as transplants for people who are blind, says Gopalakrishnan.
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In the past few years, it has become possible to encourage stem cells 鈥� versatile cells similar to those found in embryos 鈥� to grow into spherical masses of brain tissue up to three millimetres wide, known as brain organoids.
Now the team has managed to get brain organoids to form optic cups, an early stage of eye formation, which normally begins when human embryos are about five weeks old. The researchers did this by adding retinoic acid, a vitamin A derivative involved in eye development in the embryo, 20 days into their development.
Two of the structures, each 0.2 millimetres wide, formed in about 65 per cent of 314 brain organoids that the team treated in this way. As well as a primitive lens and retina, other eye tissues seen include the cornea, a clear tissue that covers the front of the eye, and neurons that grew from the optic cup into the rest of the brain tissue.
It is unclear how similarly these tissues function to their full-grown counterparts, but when the organoids are exposed to light, electrical signals travel along the neural pathways, suggesting that some kind of visual information is being transmitted. It is significant that most of the brain organoids form a symmetrical pair of optic cups, rather than a random number of them, says Gopalakrishnan. 鈥淭he stem cells are smart enough they remember what they want to generate.鈥�
The team鈥檚 next step will be to try to keep the organoids alive for longer, as at the moment they start breaking apart after about 80 days in the dish, probably because they have no blood supply.
Cell Stem Cell
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