Download Human `Mini-Brain`..... Cerebral Organoids produced in a laboratory!

Human 'Mini-Brain'.....
Cerebral Organoids produced in a laboratory!
Science 30 August 2013:
Vol. 341 no. 6149 pp. 946-947
DOI: 10.1126/science.341.6149.946
No bigger than apple seeds, the cell clusters are simply referred to as "cerebral
organoids." But that careful language in a paper in this week's issue
of Nature belies the excitement of many neuroscientists at what it reports: the
growth from human embryonic stem cells of semiorganized knots of neural tissue
that contain the rudiments of key parts of the human brain, including the hippo
campus and prefrontal cortex.
"I find it amazing," says Wieland Huttner, a neuroscientist at the Max Planck
Institute of Molecular Cell Biology and Genetics in Dresden, Germany, who was
not involved in the study. "It's not real brain—that's clear. But I'm positively
surprised that so many features are reproduced." Developmental geneticist
Madeline Lancaster and her colleagues, who grew the organoids in a Vienna
laboratory, have already shown that they can use the organoids to probe how
normal human brain development goes awry in a genetic brain disorder.
Left to their own devices in a lab dish, embryonic stem (ES) cells will differentiate
into a menagerie of tissues: beating heart cells, neurons, even hair and teeth. The
trick for scientists has been to harness that potential, coaxing the cells to grow
into the kinds of tissues they want to study or use for a therapy.
Developmental biologists know that neural tissue is a sort of default fate for
differentiating embryonic cells, and researchers have been able to grow a variety
of specific neural cell types from ES cells. But the level of cellular organization
seen in this latest brain-in-a-dish paper is a significant step forward, says
Magdalena Götz, who studies neurodevelopment at the Ludwig Maximilian
University of Munich in Germany.
Lancaster's work took place in the lab of Jürgen Knoblich, a developmental
geneticist at the Institute of Molecular Biotechnology of the Austrian Academy of
Science in Vienna. It exploits what Knoblich calls the "absolutely enormous selforganizing capacity of developing human cells. If you just leave them alone and
provide a medium that is supportive enough, they do things on their own." It also
builds on work by Yoshiki Sasai of the RIKEN Center for Developmental Biology
in Kobe, Japan. In 2008, he and his colleagues reported that mouse and human
ES cells in culture could spontaneously form cell layers that resemble the cortical
layers in the brain.
Lancaster, a postdoctoral researcher in Knoblich's lab, was trying to culture early
neural tissue to better understand how and when developing brain cells switch
from proliferation—making more of themselves—to differentiation—making more
mature cell types, which don't continue to divide. Lancaster started with
techniques developed by Sasai and others that shepherd dividing stem cells
toward a neural fate, but she was also intrigued, she says, by the "miniguts" that
another research team had grown in droplets of Matrigel, a gelatinous protein
mixture that can help cells grow in three dimensions. So she embedded clusters
of stem cell–derived neural cells in a droplet of the material (see diagram).
The Matrigel droplets freed the cell clusters to grow larger and develop more
complex structures, without any further coaxing. To increase the availability of
oxygen and other nutrients to the inner layers of the structures, Lancaster put the
Matrigel droplets into a slowly rotating bioreactor, which gently shakes them.
Within a few weeks, Lancaster says, she noticed darker pigmented patches on
some of the cell clusters. On closer inspection, she recognized the rudiments of
eye tissue, a sign that more complex structures might be forming. When she
described the data at a lab meeting, Knoblich says, "I was completely blown
away. I couldn't sleep that night."
When lab members looked inside some of the cerebral organoids, they found
structures that resemble the choroid plexus (the cavity in the brain that produces
cerebrospinal fluid), the cerebral cortex (the brain's outermost layer), and retinal
tissue. More detailed staining showed evidence that after 16 days of
development, the organoids had what resembles forebrain, midbrain, and
hindbrain regions. The team also found molecular markers for a variety of more
specialized regions—including the outer subventricular zone (OSVZ), a feature of
human, but not mouse, brains. Organoids grown from mouse ES cells did not
develop an OSVZ region.
The resemblance to a real brain only goes so far. The organoids do not have any
blood vessels, so cells at their core die. They reach their maximum size—about 3
millimeters in diameter—after 2 to 3 months, Lancaster says, and after 4 months
they don't develop any new cell types. However, the cell clusters can apparently
survive indefinitely in the bioreactor; the oldest ones have been in culture for
nearly a year, the researchers report.
The cerebral organoids may shed light on human brain diseases that are difficult
to study in mice or other animals. For example, the scientists used the structures
to study microcephaly, a neurodevelopmental disorder in which the head and
brain end up much smaller than normal. Rather than starting with ES cells, they
took cells from a person with a particular form of the disorder and
"reprogrammed" them into so-called induced pluripotent stem (iPS) cells. Mice
are a poor model for that form of microcephaly; the specific genetic mutation
responsible results in mice with brains that are only slightly smaller than normal.
In contrast, organoids derived from the patient's iPS cells were shrunken, and
Knoblich's team found a clue to why. Certain precursor cells were maturing
earlier than normal, bringing tissue growth to a halt prematurely.
The organoids are probably not yet useful for studying more complex
neurodevelopmental conditions such as autism or schizophrenia, because those
conditions involve more mature cells and complex cell connections. Lancaster
and Knoblich also note that each organoid develops distinctively, resulting in
significant differences in composition and structure that make it hard to do
controlled experiments.
The researchers are working on ways to grow more consistent organoids—and to
incorporate some sort of vascular system so that the cell clusters can grow
bigger and presumably develop further. They hope that additional teams will take
up and improve the method. Götz and others says they plan to do just that. "For
studying the cerebral cortex, this is the best model so far," she says. "People will
use it, and time will tell how useful it is."