Scientists Grew Stem Cell ‘Mini Brains’. Then, The Brains Sort-of Developed Eyes

Science Alert – by Michelle Starr

Mini brains grown in a lab from stem cells have spontaneously developed rudimentary eye structures, scientists report in a fascinating new paper.

On tiny, human-derived brain organoids grown in dishes, two bilaterally symmetrical optic cups were seen to grow, mirroring the development of eye structures in human embryos. This incredible result will help us to better understand the process of eye differentiation and development, as well as eye diseases.

“Our work highlights the remarkable ability of brain organoids to generate primitive sensory structures that are light sensitive and harbor cell types similar to those found in the body,” said neuroscientist Jay Gopalakrishnan of University Hospital Düsseldorf in Germany.

“These organoids can help to study brain-eye interactions during embryo development, model congenital retinal disorders, and generate patient-specific retinal cell types for personalized drug testing and transplantation therapies.”

Brain organoids are not true brains, as you might be thinking of them. They are small, three-dimensional structures grown from induced pluripotent stem cells – cells harvested from adult humans and reverse engineered into stem cells, that have the potential to grow into many different types of tissue.

In this case, these stem cells are coaxed to grow into blobs of brain tissue, without anything resembling thoughts, emotions, or consciousness. Such ‘mini brains’ are used for research purposes where using actual living brains would be impossible, or at the very least, ethically tricky – testing drug responses, for example, or observing cell development under certain adverse conditions.

This time, Gopalakrishnan and his colleagues were seeking to observe eye development.

In previous research, other scientists had used embryonic stem cells to grow optic cups, the structures that develop into almost the entire globe of the eye during embryonic development. And other research had developed optic cup-like structures from induced pluripotent stem cells.

Rather than grow these structures directly, Gopalakrishnan’s team wanted to see if they could be grown as an integrated part of brain organoids. This would add the benefit of seeing how the two types of tissue can grow together, rather than just growing optic structures in isolation.

“Eye development is a complex process, and understanding it could allow underpinning the molecular basis of early retinal diseases,” the researchers wrote in their paper.

“Thus, it is crucial to study optic vesicles that are the primordium of the eye whose proximal end is attached to the forebrain, essential for proper eye formation.”

Previous work in the development of organoids showed evidence of retinal cells, but these did not develop optic structures, so the team changed their protocols. They didn’t attempt to force the development of purely neural cells at the early stages of neural differentiation, and added retinol acetate to the culture medium as an aid to eye development.

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