Cultured in a dish, stem cells spontaneously assembled themselves into a complex structure resembling an eye – a retina, to be exact.
It could one day provide an endless supply of cells for ‘the next generation of generative medicine in retinal degeneration therapeutics,’ according to the authors.
- First, scientists led by Yoshiki Sasai at the RIKEN Center for Developmental Biology grew floating clusters of embryonic stem cells from mice in a carefully crafted culture medium. The dish included proteins, like “a bandage to the tissue,” Sasai says. “Without that, cells tend to fall apart.”
- Over 12 days, the cells eventually organized themselves into a 3-D, layered structure reminiscent of an optic cup (pictured) – which forms the inner and outer layers of the retina during normal development.
The optic cup is brandy-snifter-shaped organ that has two distinct cell layers. The outer layer – that nearest to the brain – is made up of pigmented retinal cells that provide nutrients and support the retina. The inner layer is the retina itself, and contains several types of light-sensitive neuron, ganglion cells that conduct light information to the brain, and supporting glial cells.
The ‘retina in a dish’ is by far and away the most complex biological tissue engineered yet.
What's so surprising about the self-directed organization of the stem cells is how the culture started as a patternless collection of cells that weren’t pushed or pressured to become any particular thing. The optic cup's formation depends on some intrinsic, self-organizing program directing the fate and position of cells.
Though the optic cups may look and develop like the real thing, there may be differences between what's synthetic and what happens normally. The team hasn’t shown if the optic cups can sense light or transmit impulses to the brain.
If the technique can be adapted to human retinas (which develop similarly to mouse ones) and proved safe for transplantation, it could offer an unlimited well of tissue to replace damaged retinas.
Retinitis pigmentosa and age-related macular degeneration are the most common causes of blindness in old age, and involve the gradual and normally irreversible destruction of retinal cells.
For now, retinas created from reprogrammed stem cells from patients with eye diseases could be used to screen drugs or test gene therapies.
The study was published today in Nature.
Image: optic cup in a test tube / M. Eiraku and Y. Sasai at RIKEN