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New definition of a human embryo proposed amid rapid scientific advances

When someone says the word embryo, what do you think of? Probably that picture you’ve seen a thousand times on a thousand different news articles: a translucent orb swelling with cytoplasm being prodded by a microinjection needle under the light of a microscope. The mainstreaming of IVF, or in vitro fertilization, has familiarized new generations of people with what the earliest stages of human development entails. But earlier this summer, when scientists revealed they’re now able to create blobs of stem cells in the lab that self-organize into the same sorts of structures embryos themselves build during those first few weeks, it blasted wide open whatever ideas of the embryo we used to have.…

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Featured

 Are human embryo models a cause for hope or alarm?

A recent breakthrough in the race to create ‘synthetic’ embryos has sparked criticism. But the findings could be valuable in understanding miscarriages and genetic disorders

 New Human Embryo Models Spark Needless Controversy

Recent news of complex embryo models revived debates over stem cells and human cloning. But biology says there’s nothing to worry about.

Articles of Interest

First Human Embryos 'Edited' in U.S.—Get the Facts

What if you could remove a potentially fatal gene mutation from your child’s DNA before the baby is even born? In an advance that's as likely to raise eyebrows as it is to save lives, scientists just took a big step toward making that possible. For the first time, researchers in the United States have used gene editing in human embryos. As they describe today in the journal Nature, the team used “genetic scissors” called CRISPR-Cas9 to target and remove a mutation associated with hypertrophic cardiomyopathy, a common inherited heart disease, in 42 embryos.

Game-Changer: The First Synthetic Human Embryos Now Exist

But they immediately raise serious ethical questions.

Human embryogenesis

Embryogenesis, the first eight weeks of development after fertilization, is an incredibly complicated process. It’s amazing that in eight weeks we’re transforming from a single cell to an organism with a multi-level body plan. The circulatory, excretory, and neurologic systems all begin to develop during this stage. Luckily, like with many complex biological concepts, fertilization can be broken down into smaller, simpler ideas. The big idea of embryogenesis is going from a single cell to a ball of cells to a set of tubes.

Limits for human embryo research have been changed: this calls for public debate

For 40 years, research into early human development has been guided by the principle that after 14 days, an embryo should not be used for research and must be destroyed. This rule has been part of the law of more than 12 countries. But new guidelines released by the International Society for Stem Cell Research have removed this rule. This makes it possible to conduct research on human embryos that are at more advanced stages of development. Now, countries must revise their laws, policies and guidelines to reflect this change. But first, public debate is crucial to determine the limits of what sort of research should be allowed.

Re-defining the human embryo: A legal perspective on the creation of embryos in research

Scientific advances in reproductive biology have made impressive achievements that seemed impossible thirty years ago (Villalba et al, 2023). The creation of embryos through techniques such as somatic cell nuclear transfer (SCNT) in the 1990s was only the first step in a great chain of milestones.

Researchers are Now Editing Genomes of Human Embryos

Researchers are finding ever more powerful ways to use the genome editing tool CRISPR. In the latest, a UK group used the technology to remove a critical gene needed for human development in order to learn more about the earliest steps of how embryos form.

Scientists Create First Cloned Human Embryo

The process that created Dolly the sheep in 1996 has now been proven successful in humans.

Scientists Create Living Entities In The Lab That Closely Resemble Human Embryos

For decades, science has been trying to unlock the mysteries of how a single cell becomes a fully formed human being and what goes wrong to cause genetic diseases, miscarriages and infertility. Now, scientists have created living entities in their labs that resemble human embryos; the results of two new experiments are the most complete such "model embryos" developed to date.

Scientists Debut Lab Models of Human Embryos

Four teams have coaxed human stem cells to organize themselves into embryo-like forms. The advance could shed light on fertility.

Scientists grow whole model of human embryo, without sperm or egg

The Weizmann Institute team say their "embryo model", made using stem cells, looks like a textbook example of a real 14-day-old embryo. It even released hormones that turned a pregnancy test positive in the lab. The ambition for embryo models is to provide an ethical way of understanding the earliest moments of our lives. The first weeks after a sperm fertilises an egg is a period of dramatic change - from a collection of indistinct cells to something that eventually becomes recognisable on a baby scan.

Studying Life

Because of medical and ethical challenges, there’s much we don’t know about the first few weeks of human embryo development, says biologist Jacob Hanna of Israel’s Weizmann Institute of Science. Hanna’s team used naive stem cells treated with chemicals to nudge them into becoming four types of cells found in early embryos. One percent of the treated stem cells spontaneously formed a structure similar to a human fetus, which researchers allowed to grow for 14 days. While distinctly not human, the model is close enough to give researchers potential insights into fertility, miscarriage, and more, for the first time.

Synthetic human embryos let researchers study early development while sidestepping ethical and logistical hurdles

However, advances in genetic engineering and molecular and cellular biology have catalyzed the emergence of synthetic embryology, a subfield dedicated to replicating and studying embryonic development in a petri dish using human stem cells. By offering new tools to explore the enigmatic earliest stages of human development, synthetic embryology can help researchers overcome the challenges of using real human embryos.

What is a human embryo? A new piece in the bioethics puzzle

The controversy surrounding the human embryo is a long-standing one. Thirty years ago, there was already an intense debate over moral and legal status of the human embryo and its moral, legal, and political implications. This controversy is still very much alive. In fact, the emergence of modern technologies in the recent years has made the debate even more complicated. Today, we not only debate how to treat the human embryo, but we are also faced with a renewed discussion about what the embryo is. The issue cannot be addressed from a purely scientific point of view since it includes elements that go far beyond biology.

‘Human Embryo’ – A Biological Definition

There has been a consensus within the scientific literature that a human embryo is an entity in its earliest stages of development that is less than eight weeks gestation (Geller, 2003; Moore and Persaud, 2003; Jones, 1997). After eight weeks it is then considered to be a foetus. However, there is a difference of opinion as to which points of biological development should be covered by the term ‘embryo’.

Resources

The Multi-Dimensional Human Embryo

The Multi-Dimensional Human Embryo is a collaboration funded by the National Institute of Child Health and Human Development (NICHD) to produce and make available over the internet a three-dimensional image reference of the human embryo based on magnetic resonance imaging. The collection of images is intended to serve students, researchers, clinicians, and the general public interested in studying and teaching human development.

The Virtual Human Embryo

This $3.2 million, 11-year initiative engaged a team led by Dr. Raymond F. Gasser—one of the leading embryologists of the last half century. His team created thousands of restored, digitized, and labeled serial sections from the world's largest collection of preserved human embryos. They used these serial sections to create animations, fly-throughs, and 3-D reconstructions.