From mouse stem cells, researchers from the University of Cambridge have
built model embryos with a brain, a heart that beats, and the building
blocks for every other organ in the body. It represents a fresh way to
recreate the beginnings of life.
The embryo model was created by the study team without the use of eggs or
sperm, under the direction of Professor Magdalena Zernicka-Goetz. Instead,
they made use of stem cells, which are the body's master cells and may
differentiate into practically any form of cell.
The researchers imitated natural processes in the lab by directing the
three varieties of stem cells that are present in early mammalian
development to the point where they begin interacting. By increasing the
expression of a certain set of genes and creating a special environment for
their interactions, the researchers were able to induce the stem cells to
"speak" to one another.
The stem cells self-organized into structures that developed through the
various phases of development until they had beating hearts and the brain's
structural components. They also contained the yolk sac, which provides
nutrition to the embryo during its early weeks of development. The
Cambridge-developed models, in contrast to earlier synthetic embryos,
progressed to the stage where the complete brain, including the anterior
region, began to form. In comparison to previous stem cell-derived models,
this represents a later stage of development.
The team believes that their findings might aid in the understanding of why
some embryos do not grow into healthy pregnancies while others do. The
outcomes might also be utilized to direct the production and repair of
artificial human organs for transplantation. The study was published on
August 25, 2022, in the magazine Nature. It is the outcome of more than ten
years of research that has steadily produced increasingly complicated
embryo-like structures.
According to Zernicka-Goetz, a professor in the Department of Physiology,
Development, and Neuroscience at Cambridge University who specializes in
mammalian development and stem cell biology, "our mouse embryo model not
only develops a brain but also a beating heart, all the components that go
on to make up the body." "How we've come this far is absolutely astounding.
Our community has long held this as a goal, and after ten years of hard
effort, we have finally achieved it.
A healthy development of a human embryo requires a "dialog" between the
tissues that will create the embryo and the tissues that will connect the
embryo to the mother. In the first week after fertilization, three distinct
stem cell types start to emerge; one of these will eventually develop into
the body's tissues, while the other two aid in the growth of the embryo. The
placenta, which links the fetus to the mother and supplies oxygen and
nourishment, will develop from one of these extraembryonic stem cell
varieties. The yolk sac is the second, where the embryo develops and
receives its initial nutrition.
When the three different stem cell types start communicating with one
another and giving instructions to the embryo on how to develop
appropriately, many pregnancies end prematurely.
The majority of women don't even recognize they are pregnant at this point,
according to Zernicka-Goetz, a professor of biology and biological
engineering at Caltech. "This stage of pregnancy serves as the building
block for all that comes after. It will fail, and the pregnancy won't
succeed.
Over the past ten years, the Cambridge research team of Professor
Zernicka-Goetz has been examining these first few weeks of pregnancy in an
effort to comprehend why some pregnancies end in failure and others in
success.
The stem cell embryo model is crucial, according to Zernicka-Goetz, since
it provides access to the growing structure at a stage that is often
inaccessible to humans due to the implantation of the small embryo into the
mother's womb. This accessibility enables us to modify genes in a model
experimental setting to comprehend their developmental roles.
The researchers assembled cultivated stem cells that represented each of
the three tissue types in the proper ratios and environments to encourage
their growth and communication with one another, finally self-assembling
into an embryo.
In order to guide the development of the embryo, extraembryonic cells
communicate with embryonic cells not just chemically but also
mechanistically, or by touch.
"This stage of human life is so enigmatic, so to be able to watch how it
develops in a laboratory — to have access to these specific stem cells, to
understand why so many pregnancies fail and how we might be able to prevent
that from happening — is pretty extraordinary," said Zernicka-Goetz. "We
examined the conversation that has to take place between the various stem
cell types at that time - we've showed how it happens and how it might go
awry."
The capacity to synthesize the full brain, especially the anterior portion,
which has been a primary aim in the creation of synthetic embryos,
represents a significant advancement in the field. Because this area of the
brain needs signals from one of the extraembryonic tissues to grow, this is
effective in Zernicka-technique. Goetz's From their 2018 and 2021 trials,
which employed the same component cells to grow into embryos at a somewhat
earlier stage, the scientists hypothesized that this may be happening. They
can now declare with certainty that their model is the first to indicate
growth of the anterior, and in fact the entire brain, by delaying
development by only one day.
According to Zernicka-Goetz, "this gives new opportunities to research the
mechanics of neurodevelopment in an experimental model." In reality, by
disrupting a gene previously known to be crucial for the development of the
neural tube, a forerunner to the nervous system, as well as the brain and
eyes, we provide the confirmation of this notion in the work. The synthetic
embryos exhibit the same recognized problems in brain development as an
animal with this mutation when this gene is absent. As a result, we may
start using this method on the many genes whose role in brain development is
unknown.
While the present study used mouse models, analogous human models are being
created by the researchers with the capacity to generate certain organ
types. This will help them understand the mechanisms behind critical
processes that would otherwise be hard to investigate in actual embryos. Up
to the 14th day of development, human embryos may only be researched in the
lab under current UK law.
The techniques used by Zernicka-team Goetz's might also be used to direct
the creation of synthetic organs for patients awaiting transplants if they
are later demonstrated to be effective with human stem cells.
"There are so many individuals waiting for organ transplants all across the
world," said Zernicka-Goetz. The possibility of using the information gained
from our research to develop accurate synthetic human organs to save lives
that are now being lost is what makes our work so thrilling. With our
current understanding of how adult organs are created, it should also be
able to modify and cure them. I never imagined we would get to this point,
but it took ten years of arduous labor from many of my team members. Your
dreams have come true, even if you never thought they would.
Scientist Magdalena Zernicka-Goetz has produced a remarkable
discovery.
The result of a decade's worth of research is the development of synthetic
mouse embryos that grow in a test tube and build hearts and brains using
just embryonic stem cells.
Magda explains: The mechanism of embryogenesis intrigues me. Every embryo
goes through the same process: from one cell to many, they multiply,
interact, and organize into a structure that serves as the model for all
adult body parts. However, how can embryonic cells decide what to do with
their lives, where to go, and how to behave? How do they create the right
components at the right time and place?
The process of creating the initial "synthetic embryo" models was one we
completed piece by piece. When we started, we were aware that embryonic stem
cells could be cultivated in the lab forever and that, when injected into an
embryo, they could be able to become any tissue in the adult creature. The
difficult part was directing them to grow into a full embryo. We employed
two types of extraembryonic tissue in addition to embryonic stem cells: one
kind produces the placenta, and the other is a pouch in which the embryo
grows. These tissues are crucial because they act as messengers, telling the
embryo when and where to grow each of its components.
Combining stem cells from each of these three different tissue types is
more difficult than it seems. We needed to find a setting where all three
different cell types could develop and interact. Additionally, we had to
determine the proper ratios of each cell type and add them in the proper
order. Once these fundamental concepts were established, the stem cells took
care of the rest. They self-organized to advance through a series of
developmental phases until they had beating hearts and the building blocks
for brains.
Our success was largely a result of thinking outside the box. Studies using
embryo models most often concentrate on embryonic stem cells without taking
into account the important role of extraembryonic cells. The appropriate
ratios of extraembryonic and embryonic stem cells were combined.
Extraembryonic cells communicate with embryonic cells through a variety of
methods, including chemical messages and mechanically "by touch." Our
research is assisting in the comprehension of these signaling events.
In order to understand the mechanics underlying critical events that would
otherwise be difficult to examine, we are creating a comparable model of the
human embryo. This is significant since the vast majority of human
pregnancies end in miscarriage at this point of development for unknown
reasons. Additionally, it will enable us to pinpoint the conditions
necessary for the formation of healthy human tissues into various
organs.
We've learned a lot about the processes by which the embryo creates itself
thanks to the new "synthetic embryo," which was created. We learned how
cells move between compartments as the multi-layered body plan emerges, how
the extraembryonic tissues direct embryonic stem cells along the proper
pathways to signal formation of the correct structures, and how this
appropriately sets the stage for neurulation — the process where tissue
folds to form the neural tube and, in turn, the brain and spinal cord.
When the small embryo implants into the mother's womb, a stage that is
often concealed from us, this model allows us access to the growing
structure. We are able to see the embryo's growth as it moves through that
stage since our model does not need to implant in order to grow. This
accessibility allows us to modify genes to understand their developmental
roles in a model experimental setting.
It is unquestionably true that perseverance and enthusiasm are necessary
for this kind of activity. In the communist-run Poland where I was raised,
travel was prohibited and unconventional thought was discouraged. Many of us
rebelled against the intense social pressure to fit in, which was there.
This has the benefit of inspiring a drive to think for oneself and to
persevere in the face of setbacks. That also affected how I became a
scientist.
I developed methods to analyze the "developmental black box" — the embryo's
development at the moment of implantation — when I founded my research group
in Cambridge. During my PhD, my advisors had discouraged me from pursuing it
because they thought it could be challenging to beam light inside this
"box." However, I was so intrigued by the topic of how the embryo
self-organizes that I persisted because we have made progress little by
little.
I would advise all aspiring scientists to follow their hearts. Study a
subject that interests you, and select a professor who can accommodate your
working style. Young scientists should be mentored in the lab, but they
should also be given room to express their uniqueness. According to my
observations, when women in science advance in their jobs, they face more
difficulties. It's crucial to have mentors who understand how to reconcile
science with ordinary life, including establishing a family, at later
stages.
I was shocked when an early screening revealed anomalies during my own
pregnancy. I awaited the amniocentesis, which collects fetal cells that had
gotten into the amniotic fluid since the sampling was of extraembryonic
cells. These were typical, which helped to calm my concerns. My research on
mosaic aneuploidy, a condition in which chromosomally normal cells coexist
with cells with the incorrect number of chromosomes, was sparked by this
event. Amazingly, we discovered that by removing these defective cells, the
regular, healthy cells were able to fill their place. We're still attempting
to figure out why and how this system doesn't work in the tissues that form
the placenta.
Science is difficult, labor-intensive, and consumes the majority of your
waking hours. I unwind by watching movies. I watch a lot of documentaries,
art films, and international films in Polish, French, and Danish. But I
watch dramas when I want to lose myself in a different story. I just become
a convert to gardening, where I can support the growth of other living
forms!
Being able to see the beginnings of a new life up close and personal is an
amazing sensation and a privilege. It's similar like finding a brand-new
planet that we were unaware even existed.
Reference: “Synthetic embryos complete gastrulation to neurulation and
organogenesis” by Gianluca Amadei, Charlotte E. Handford, Chengxiang Qiu,
Joachim De Jonghe, Hannah Greenfeld, Martin Tran, Beth K. Martin,
Dong-Yuan Chen, Alejandro Aguilera-Castrejon, Jacob H. Hanna, Michael
Elowitz, Florian Hollfelder, Jay Shendure, David M. Glover and Magdalena
Zernicka-Goetz, 25 August 2022, Nature.
