In what is considered a global breakthrough, biologists have grown mouse embryo models in the laboratory without the need for fertilized eggs, embryos or even a mouse, using only stem cells and a special incubator.
This achievement, published in the journal Cell by a team led by researchers at the Weizmann Institute of Science in Israel, is a highly sophisticated model of what happens during the early development of mouse embryos, at the stage just after the implementation
This is a crucial stage: in humans, many pregnancies are lost around this stage, and we don’t really know why. Having models provides a way to better understand what can go wrong and possibly information about what we can do about it.
The smallest cluster
What is particularly interesting about the newly published model is its very complex structure; it not only mimics the cell specification and design of an early-stage body plan, including the precursors of the heart, blood, brain and other organs, but also “support” cells such as those found in the placenta and other tissues necessary to establish and maintain a pregnancy.
The early stages of pregnancy are difficult to study in most animals. Embryos are clusters of tiny, microscopic cells that are difficult to locate and observe inside the uterus.
But we do know that at this stage of development, things can go wrong; for example, environmental factors can influence and interfere with development, or cells do not receive the proper signals to fully form the spinal cord, as in spina bifida. Using models like this, we can begin to ask why.
However, while these models are a powerful research tool, it is important to understand that they are no embryos
They replicate only some aspects of development, but do not fully reproduce the cellular architecture and developmental potential of embryos derived after fertilization of eggs by sperm, so-called natural embryos.
The team behind this work points out that they were unable to develop these models beyond eight days, while a normal mouse pregnancy lasts 20 days.
Are ‘synthetic embryos’ of humans on the horizon?
The field of embryo modeling is advancing rapidly, with new advances emerging every year.
In 2021, several teams managed to get human pluripotent stem cells (cells that can become any other type of cell) to aggregate in a petri dish, mimicking the “blastocyst”. This is the earliest stage of embryonic development just before the complex process of implantation, when a mass of cells adheres to the wall of the uterus.
Researchers using these human embryo models, often called blastoids, have even been able to begin exploring implantation in a dish, but this process is much more difficult in humans than in mice.
Growing human embryo models of the same complexity as has now been achieved with a mouse model remains a distant proposition, but one we should still consider.
Importantly, we must be aware of how representative this model would be; a so-called synthetic embryo in a petri dish will have its limitations on what it can teach us about human development, and we need to be aware of that.
Read more: Researchers have grown ‘human embryos’ from skin cells. What does this mean and is it ethical?
No embryonic modeling can happen without a source of stem cells, so when it comes to thinking about the future use of this technology, it is vital to ask: where do these cells come from? Are they human embryonic stem cells (derived from a blastocyst) or are they induced pluripotent stem cells? The latter can be made in the laboratory from skin, or blood cells, for example, or even derived from frozen samples.
An important consideration is whether using cells for this particular type of research, trying to mimic an embryo in a dish, requires specific consent. We should think more about how this area of research will be governed, when it should be used and by whom.
However, it is important to recognize that there are international stem cell research laws and guidelines that provide a framework for regulating this area of research.
In Australia, research involving human stem cell embryo models would require a license, similar to that required for the use of natural human embryos under law in place since 2002. However, unlike other jurisdictions, Australian law also dictates how long investigators can grow. human embryo models, a restriction that some researchers would like to see changed.
Regardless of these or other changes in how and when human embryo research is conducted, there needs to be a larger community discourse on this issue before a decision is made.
There is a distinction between banning the use of this technology and technologies such as cloning in humans for reproductive use and allowing research with embryonic models to advance our understanding of human development and developmental disorders that we cannot answer for either other medium
Science is moving fast. While this stage is mostly about mice, now is the time to discuss what this means for humans and consider where and how we draw the line in the sand as the science evolves.
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