*This content was produced by experts from the Weizmann Institute of Sciences, one of the world’s most important centers for multidisciplinary basic research in the field of natural and exact sciences, located in the city of Rehovot, Israel.
There was a time when we were nothing more than a mass of densely packed stem cells. Over time, this mass elongated, sprouting limbs on both sides, buttocks on the back, a stomach on the front, and a head on top.
The process by which embryonic stem cells give rise to different organs, rescuing us from an amorphous destiny, it happens thanks to the morphogensmolecules that are made at specific times and places within the embryo and dispersed to dictate the location and shape of our organs. Varying concentrations of morphogens serve as a map that guides stem cells toward their destination.
Morphogen concentration maps are key for all technologies aimed at make organoidsthe miniature, lab-made versions of living organs that have taken the world of developmental biology by storm in the past decade.
But until now, most researchers have been producing organoids using uniform concentrations of morphogens in Petri dishes, which limited them to growing small sections of an organ in each dish, rather than generating a single one. miniature version of the complete organ.
Now, however, researchers from the University of Michiganwhich were led by Professor Jianping Fu and Dr. Xufeng Xue, together with a team from Weizmann Institute of Science and of the University of Pennsylvania have created a miniature version of the entire central nervous system embryonic, from the brain to the lower part of the spinal cord, using a microfluidic chip which mimics the dispersal of morphogens during embryonic development.
The new chip will allow researchers to ask completely new questions, both about the development of a healthy embryo as about diseases and tissue damage, according to the professor Orly Reinerfrom the Weizmann Department of Molecular Genetics, a participant in the study. He has been studying for more than 30 years diseases that affect the developing brain and began growing organoids in his laboratory a decade ago.
“In previous studies, organoids had already been exposed to varying concentrations of morphogens, but in those studies only small sections of the central nervous system were generated, for example, only the spinal cord or the forebrain, but not both,” he explains.
The microfluidic chip allows researchers to pour morphogensfrom almost any direction and at any time they wish, in deposits containing the organoids.
In the center of the chip are narrow, adhesive surfaces 4 millimeters long, like the central nervous system of a one-month-old embryo. Stem cells are embedded along these surfaces, which are then covered with a gel that simulates the extracellular environment, allowing them to develop into three-dimensional tissue.
In a short period of time, the cells spontaneously organize into a hollow tube. After three days, through a reservoir at one end of the chip, the researchers begin adding morphogens, which slowly diffuse throughout the tissue.
The researchers soon saw that the stem cells on the chip matured and became a variety of different cell types embryonic central nervous system.
The side of the chip with the highest concentration of morphogens gave rise to cells that developed at the end of the spinal cord, followed by cells destined for the middle part of the spinal cord, the hindbrain, the midbrain, and, at the far end. distant, the forebrain.
“When we characterized the new organoids, we saw perfect order along the entire length of the central nervous system, as it appears in the early embryonic stage”says Reiner.
Once the longitudinal tube of the central nervous system was created, researchers faced another challenge: emulating the development of the embryo’s forebrain along the ventrodorsal axis.
Two types of important cells that are essential for the functioning of the adult brain are normally generated in the forebrain: excitatory neuronswhich stimulate neuronal activation, and inhibitory neuronswhich block said activation.
“Until now, we had to grow each of these cell types in a different dish by exposing two organoids to different concentrations of morphogens and then try to join them together,” explains Reiner.
But the new microfluidic chip allowed the researchers to distribute the concentrations of morphogens in such a way that the two types of neurons were generated in the same tissue.
To do this, they first created the longitudinal tube, as described above, and on the seventh day they poured the morphogens near the forebrain, but away from the spinal cord.
In a short time, the cells that would later become inhibitory appeared inside the tubewhile those destined to become excitatory cells appeared on the outside of the tube, exactly as occurs during embryonic development.
The researchers they used color-coded proteins to reveal the identity of the cells in the organoids they produced. In four organoids that simulate the central nervous system of the embryo, magenta marks proteins associated with the development of the forebrain and midbrain, green, the hindbrain, and red, the center of the spinal cord.
The researchers point out that your chip does not emulate the early stages of development of the central nervous system. “In reality, we are skipping the early stages and taking the stem cells to the typical development stage of a four week embryo”says Reiner.
Still, within days a three-dimensional tissue formed that bore a striking resemblance to the embryo’s central nervous system, both in terms of the cells it contained and the order in which they appeared. This allowed the team to study, for example, genes involved in the differentiation of cell populations in the spinal cord, a process that was not previously understood.
The chip is already helping researchers better understand issues related to the development of the human nervous system. Reiner’s team, for example, has integrated the technology into their work and is using the chip to study how genetic diseases affect the longitudinal development of parts of the brain. They hope more researchers will use the technology to expand our understanding of a wide range of diseases that damage the nervous system.
Also participating in the study were Dr. Yung Su Kim, Dr. Norio Kobayashi, Dr. Yue Liu, Dr. Jason R. Spence, Dr. Robin Zhexuan Yan, Dr. Yu-Hwai Tsai, Shiyu Sun and Yi Zheng of the University of Michigan; Dr. Rami Yair Tshuva and Alfredo-Isaac Ponce-Arias of the Weizmann Department of Molecular Genetics; Prof. Hongjun Song, Prof. Guo-Li Ming and Dr. Richard O’Laughlin from the University of Pennsylvania; and Prof. Azim Surani and Dr. Frederick CK Wong from the University of Cambridge.
