Organoids, so called because they look like miniature organ blobs, are three-dimensional cultures of multiple cell types that mimic the makeup of an organ. Growing these structures helps scientists study various organs in the laboratory setting without using a living animal. Recently, researchers in Germany have successfully grown a new type of organoid that combines two organs: a brain and an eye-like structure.

To grow an organoid, stem cells, which have the potential to become any type of cell, are directed to become specific cell types. This is achieved by adding chemical signals in a sequence that mimics how those specific cell types, like brain cells, develop from stem cells in an embryo. Scientists previously noticed that dark, pigmented regions sometimes appear in brain organoids. This is an early sign of development of the retina, the light-sensitive part of the eye, in embryos. Dr. Elke Gabriel and colleagues added retinol acetate, a molecule that is essential for eye development, to brain organoids. They then observed that many brain organoids developed two symmetric structures that looked like early retinas. Next, the researchers determined that these eye structures contain many of the same cell types as developing eyes. The brain region of the organoid even responds when the eye structures are exposed to light, which indicates that the eye and brain structures are communicating with each other.

An organoid that combines two organ systems together, like the brain and the retina, is exciting because scientists can use it to study the interaction of those two organs in a dish. Even though organoids are not perfect models of actual organs, they allow scientists to learn more about the development, biology, and pathology of a complex organ. Organoids can even grow from cells donated by patients and could someday be used to determine personalized drug treatments or to grow tissues for transplantation.

This study was led by Dr. Elke Gabriel, now a post-doctoral fellow at the Institute of Human Genetics and Anthropology at the Heinrich Heine Universität in Germany. Corresponding author Dr. Jay Gopalakrishnan is a Professor and group leader of the Laboratory for Centrosome and Cytoskeleton Biology at the Heinrich Heine Universität in Germany. 

Managing Correspondent: Gemma Johnson

Press Articles: “A look at ‘eyes on the brain organoids’ Cell Stem Cell paper,” The Niche, “Scientists Grew a Brain-Like Blob With Primitive Eyes,” Gizmodo, “Brain organoids develop optic cups that respond to light,” ScienceDaily

Original Journal Article: “Human brain organoids assemble functionally integrated bilateral optic vesicles,” Cell Stem Cell

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