Human neural organoids, derived from pluripotent stem cells, enable the study of the highly regulated process of human brain development in vitro. In vivo, the process is shaped by strict time- and space-dependent morphogen gradients. Now, researchers have developed a method that leads to the development of a new cortex organoid that better represents the human brain.

The new brain organoids are composed of a single, self organized apical-out neuroepithelium, ENOs (expanded neuroepithelium organoids), unlike standard brain organoid protocols in which multiple and independent neuroepithelium units (rosettes) are formed.

Brain organoid
3D imaging of novel brain organoid viewed from different angles. The different colors represent different cell types present in the organoid. [Benedetta Artegiani, Delilah Hendriks, Anna Pagliaro]
Essential features of the cortex are more accurately captured in these new organoids and features like cell organization, stem cell expansion, and cell identity that more closely mimic the brain. These novel organoids may be used as a basis to model pediatric brain tumors.

This work is published in Nature Communications, in the paper, “Temporal morphogen gradient-driven neural induction shapes single 3 expanded neuroepithelium brain organoids with enhanced cortical identity.”

The new findings show that the newly generated cortex organoid more closely represents the human brain in multiple aspects: their shape, their architectural organization, and several properties of their cells.

“The current brain organoid models generally have several developmental structures acting like an ‘independent’ small developing brain, within one organoid,” noted Benedetta Artegiani, PhD, research group leader at the Máxima Center. “Researchers have tried for a long time to mitigate the formation of these multiple structures. To diminish variability, increase reproducibility, better recreate the brain’s different cellular identities, and ultimately to recapitulate brain development more closely. Now in this research, the new organoid model is composed of this self-organizing, single developing neuroepithelium.”

Brain organoids
Image of novel brain organoid model showing its characteristic convoluted shaped and extended neuroepithelium. The neurons present in the organoid are shown in different colors depending on their location within the tissue.
[Benedetta Artegiani, Delilah Hendriks, Anna Pagliaro]
“Cells in the brain are instructed to acquire their identity through molecules that act slowly in time, the so-called temporal gradients,” noted Delilah Hendriks, PhD, Oncode-researcher at the Hubrecht Institute and affiliated group leader at the Máxima Center. “This is exactly what we tried to mimic. To our surprise, it was enough to just provide one of the molecules (TGF-b) slowly step-by-step to generate brain organoids. This tiny change had an enormous impact and allowed us to generate organoids with a shape and an identity more similar to the human brain.”

More specifically, the authors wrote that they found that “a prolonged, decreasing gradient of TGF-β signaling is a determining factor in ENO formation and allows for an extended phase of neuroepithelium expansion.”

Pediatric brain tumors may derive from an unusual or mistaken developmental process and their study could benefit from these new models that better recapitulate early embryonic developmental mechanisms. The signaling molecule that the researchers used to make the organoids is often altered in childhood brain tumors, also suggesting that the onset of cancer in young children could be linked with changes in brain development. Now that the researchers understand that temporal gradients are of great importance to generate more accurate organoids, this study paves the way to develop brain organoids more and more similar to the developing human brain.

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