The cortex of the brain in a test tube
Researchers from the Max Planck Institute for Molecular Genetics have grown organoids of the human cerebral cortex with unprecedented accuracy and quality. To do this, they treated stem cells with a cocktail of three molecules for a short time at an early stage of their development. Over the following weeks, the cells formed cellular aggregates that anatomically mimic the architecture of the human cerebral cortex, including radial glial cells (oRG) – specialized stem cells that are necessary for the formation of cerebral hemispheres in humans and monkeys. This is the first time oRG cells have been successfully grown in a cell culture system.
Instructing brain Builders
The problem of creating brain organoids is to grow a pure culture of stem cells of the nervous system and force them to create multi-layered structures with the right types of cells.
Brain organoids can be grown from tissue samples, embryonic stem cells, or induced pluripotent stem cells – mature cells that have been reprogrammed to become stem cells. But the results were very contradictory from the point of view of the methodology, the source material and the heterogeneity of the obtained organoids.
Stem cells that build organoids must receive precise instructions to create a complex multi-layered structure of the brain. Finding the right instructions for the "builders" of the brain is a difficult task, different laboratories have tested many protocols and procedures with different results.
To find out which method is correct, it was necessary to standardize existing methods and develop a new protocol for creating organoids that best mimic the human cerebral cortex.
Like other groups before, the researchers used inhibitors – chemicals that "tell" the developing cell what not to turn into so that it eventually chooses the right path. They found that it is necessary to block the SMAD and WNT signaling pathways with three molecules in order to force them to turn into cortical cells. After a few weeks, the organoid is assembled by itself, without additional interventions.
A slice of an organoid with visible characteristic layers of the cerebral cortex. Blue staining indicates the presence of radial glial cells.
New protocol
The researchers used different cell lines and compared the approach in parallel, generating cortical organoids with unprecedented precision. One important achievement is that they were able to reproduce cellular diversity: while each organoid contained many different cell types, there were few differences between individual organoids. The researchers confirmed this by staining tissues and sequencing the RNA of individual cells. Organoids grown according to the new protocol demonstrated both the highest and the most stable level of cortical identity.
Some diseases associated with the development of the nervous system, such as microcephaly, have also been modeled in organoids. To do this, progenitor cells must maintain a balance between a sufficient degree of self-renewal, on the one hand, and the ability to differentiate, on the other.
Breakthrough in cell culture
Scientists have demonstrated that their organoids develop oRG cells, which are known to play a crucial role in brain development - they are responsible for the formation of brain hemispheres in primates. After 50 days of growth, the organoids are significantly enriched with this type of stem cells.
The obtained results provide a platform for further application in basic research, pharmacological trials and in the clinic. Article by D.Rosebrock et al. Enhanced cortical neural stem cell identity through short SMAD and WNT inhibition in human cerebral organoids facilitates the emergence of outer radial glial cells is published in the journal Nature Cell Biology.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru .