Yoshiki Sasai of the RIKEN Center for Developmental Biology (CBD) in Kobe, Japan, has grown the precursor of a human eye in the lab.
The structure, called an optic cup, is 550 micrometres in diameter and contains multiple layers of retinal cells including photoreceptors.
The achievement has raised hopes that doctors may one day be able to repair damaged eyes in the clinic.
But for researchers at the annual meeting of the International Society for Stem Cell Research in Japan where Sasai presented the findings this week, the most exciting thing is that the optic cup developed its structure without guidance from Sasai and his team.
The human eye is a complex structure - but the cues to build it come from inside the growing cells.
Until recently, stem-cell biologists had been able to grow embryonic stem-cells only into two-dimensional sheets.
But over the past 4years, Sasai
has used mouse embryonic stem cells to grow well-organized, 3D cerebral-cortex, pituitary-gland and optic-cup tissue.
latest result marks the first time that anyone has managed a similar feat using human cells.
In Sasai's experiment, retinal precursor cells spontaneously formed a ball of epithelial tissue cells and then bulged outwards to form a bubble called an eye vesicle.
That pliable structure then folded back on itself to form a pouch, creating the optic cup with an outer wall (the retinal epithelium) and an inner wall comprising layers of retinal cells including photoreceptors, bipolar cells and ganglion cells.
"This resolves a long debate," says Sasai
, over whether the development of the optic cup is driven by internal or external cues. last month, a group in London showed that a transplant of stem-cell derived photo-receptors could rescue vision in mice.
But the transplant involved only rods, not cones, and would leave the recipient seeing fuzzy images.
organically layered structure offers hope that integrated photoreceptor tissue could one day be transplanted.
The developmental process could also be adapted to treat a particular disease, & stocks of tissue could be created for transplant & frozen.
emphasizes that the cells in the optic cup are "pure", unlike those in two-dimensional aggregates, which may still contain embryonic stem cells.
This reduces concerns that transplants of such cells might develop cancerous growths or fragments of unrelated tissues.
M Takahashi, has already started transferring sheets of the retina from such optic cups into mice.
plans to do the same with monkeys by the end of the year.