I saw small clusters of cells. largely Like a human fetus. Made from stem cells without using eggs, sperm, or uterus, embryo model It has a yolk sac and protoplacenta, similar to the state that a real human fetus reaches after about 14 days of development. I also secreted hormones that showed a positive result on a drugstore pregnancy test.
In Jacob Hanna’s expert eyes, the model was not perfect, but more like a rough sketch. There was no chance of it growing into a real baby. But in 2022, when two students barge into his office and drag him into a microscope to show them clumps of cells, he opens the door for his team to understand a key stage in human development. I felt unlocked. Hanna, a professor at the Weizmann Institute of Science in Israel, also knew that this model raised some serious ethical questions.
You may remember images of embryo development from your high school biology textbook. In a predictable progression, the fertilized egg transforms into a mass of cells, then a bean-shaped mass, and finally something resembling a baby. But the truth is that the early stages of human development are still very immature. mystery. Early stage embryos are too small to be seen with ultrasound. By day 14, it is barely noticeable to the naked eye. It is difficult for them to survive that long outside the body. Who should do so is another question, but for decades scientific policy and regulation has set a limit on how long embryos can be grown in the lab at 14 days.
Embryonic models, or embryos created using stem cells, could offer a real alternative for studying some of the most difficult questions in human development. important details For example, about the causes of miscarriages and developmental disorders. In recent years, Hanna and other scientists have made remarkable progress in culturing pluripotent stem cells. imitate Structure and function of a real developing embryo. But even if researchers solve the technical problems, moral questions remain. When is a copy good enough to be considered the real thing? More importantly, when should a laboratory experiment be legally and ethically treated as human? Or?
surroundings Day 14 During embryonic development, an important stage of human growth called gastrulation begins. Cells begin to organize into layers that form the initial bud of the organ. primitive striped pattern Developmental precursor of the spine–appear. It is also at this point that the fetuses can no longer form twins. “You become an individual,” Jeremy Sugarman, a professor of bioethics and medicine at the Berman Institute for Bioethics at Johns Hopkins University, told me.
The primitive streak is the main rationale behind what is common. referred to As the “14 day rule”. many country The amount of time a human embryo can be kept alive in a Petri dish is limited to 14 days. When a UK committee recommended a 14-day restriction in the 1980sIn vitro fertilization, which requires keeping embryos alive until they are transferred or frozen around day 5 or 6, was still new. The Committee reasoned that 14 days is the last point at which an embryo can be definitively considered to be nothing more than a collection of cells, with no potential individual identity or individual rights. They reasoned that because the central nervous system is formed after a 14-day milestone, there is no possibility of feeling pain.
But with the recent rise of advanced embryo models, some groups are beginning to question the sanctity of the two-week mark. 2021, International Society for Stem Cell Research Relaxed 14-day guidelines, I’m saying Subject to ethical review and national regulations, the study may continue beyond 14 days. (The organization declined to set new limits.) British researchers published the results in July. A similar set of guidelines Especially for models. However, Australia’s Embryo Research Licensing Board recently decided to treat the more realistic model like the real thing, banning it from being developed for more than 14 days. Federal funding for human embryo research has been prohibited in the United States since 1996, but there are no federal laws regulating experiments using real or model embryos. “The first question is, are they embryos at all?” Hank Greeley, a Stanford University law professor and director of the Center for Law and Biological Sciences, told me. If you allow people to grow further, “Maybe they’ll grow a second head. We don’t know.” (Having a second head doesn’t necessarily disqualify people from being human. ) In the absence of an ethical agreement, Hannah works to develop the model until day 21, which corresponds to almost the end of gastrulation. So far, he said, he has managed to grow them to about 18 days old.
Researchers generally agree that: today’s The models show little danger of becoming walking, talking humans one day. Combining sperm and egg in the old-fashioned way no longer guarantees that a new life will emerge. Even for women in their 20s, approx. with a 25% chance Getting pregnant every month. Without the usual starting materials, it’s quite difficult to create embryos in the lab. Currently, only about 1% of embryo models actually resemble embryos, Hanna said. And because scientists don’t know much about what a 9-day-old embryo looks like inside the body, Greeley said they don’t really know if the model develops similarly. .
But in recent years, scientists have already achieved what seemed impossible not so long ago. Both Hanna and Magdalena Jelnicka Goetz, a developmental and stem cell biologist at the California Institute of Technology and the University of Cambridge, created A mouse model with a brain and a beating heart. Scientists and ethicists would be wise to consider what qualifies as a human before a human fetal model starts beating. The most important question, some ethicists argue, is not whether researchers can achieve a heartbeat in a petri dish, but whether they can achieve a heartbeat in a model embryo implanted in a human womb. “It’s no longer about how embryos are made or where they come from, but what they can do,” Insu Hyun, a bioethicist and director of life sciences at the Boston Museum of Science, told me. Ta. Under experiment published last yearseven-day-old model monkey embryos were successfully implanted into the uteruses of three female monkeys. Signs of pregnancy disappeared after about a week, but the papers are still there raised a ghostIt could be a human version of the experiment, or the promise of one.
Building more realistic embryo models can have tremendous benefits, starting with a basic understanding of how embryos grow. A century ago, scientists thousands of Organize the embryo samples 23 steps Covers the first eight weeks of development. These developmental snapshots, known as Carnegie stages, still form much of the basis of how early life is described in the scientific literature. The problem, Hanna said, is that “we don’t know what’s going to happen in between.” “To study development, we need living material. We need to watch it grow.” Until then recentlyscientists rarely kept embryos in the lab past day seven, leaving many questions about development beyond the first week. Most developmental disorders occur in: first semester About pregnancy. For example, cleft palate, a potentially debilitating birth defect, will develop at some point. before the 9th week Scientists still don’t understand why. This mystery may be solved by further developmental studies conducted in embryo models, Greeley said.
A deeper understanding of the early stages of life can provide insight far beyond developmental disorders. It could help clarify why some women miscarry frequently or are unable to conceive at all. Dr. Jelnicka-Goetz developed a model to study the amniotic cavity. She believes that if the amniotic cavity forms improperly, the pregnancy may fail. Embryo models could also help explain how and why prenatal development is affected by viruses, alcohol, and importantly, drugs. Pregnant people are generally excluded from clinical trials because of the potential risk to the fetus, which prevents them from receiving treatment for new chronic conditions. Hannah started company It aims, among other things, to test the safety of drugs in embryonic models. Hanna said she also envisions a more sci-fi future. The idea is to grow the embryo model to day 60, harvest the ovaries, and use the eggs for in vitro fertilization to treat infertility. Because stem cells can grow from skin cells, such a system eliminates the need for the more invasive aspects of IVF, which involves activating the ovaries with hormones and surgery to retrieve the resulting eggs, which can be triggered by old eggs. It has the potential to solve many infertility problems.
Surrealistic models of embryos may not be necessary to answer at least some of these questions. Arie Warmflush, a professor of biological sciences at Rice University, studies gastrulation, but the cells that form the placenta are not relevant to his research question, so his model omits them. he told me. “In some ways, the better the model is, the more we have to worry about it,” he says. Hyun said he was warning scientists against creating overly complex models to avoid provoking controversy, especially in a country already divided by ideas about how life began. But considering all the medical advances that can be achieved by studying realistic models, all the unknowns that are starting to look like we know, it’s hard to imagine anyone following his advice.
