Sign up for CNN’s Wonder Theory science newsletter and embark on an extraordinary journey through the universe. Delve into the latest news on captivating discoveries, remarkable scientific advancements, and more. CNN continues to ponder one of the greatest enigmas in the realm of science: the intricate process of human cell division and reproduction, which results in the creation of a human body comprising over 30 trillion cells that are invisible to the naked eye.
From the moment a sperm unites with an egg, the development of a human embryo involves a series of complex and elusive procedures. While significant knowledge about embryo development has been obtained from animal studies, such as mice, rabbits, chickens, and frogs, research involving human embryos remains heavily regulated and restricted in most countries. However, the information gathered from animal studies only provides limited insights. The enigma of human embryo development, particularly during the crucial initial month, remains largely unsolved.
Jacob Hanna, a professor of stem cell biology and embryology at the Weizmann Institute of Science in Israel, explains, “The drama lies in the first month, while the remaining eight months of pregnancy primarily involve substantial growth. However, that first month remains a mysterious black box.” The ability to peer into this black box would unlock a world of biomedical possibilities, enabling scientists to demystify a previously obscure phase of embryo development. This knowledge would ultimately contribute to a better understanding of issues such as miscarriages, congenital birth defects, and the side effects of medications taken during pregnancy.
Some researchers believe they may have found a revolutionary method to observe embryo development without relying on eggs or sperm. Through the utilization of stem cell advancements, labs worldwide have created structures resembling embryos. These clumps of cells, smaller than a grain of rice, represent the very earliest stages of human development, before organ formation takes place. They lack a beating heart and a brain. The most advanced models, unveiled by an Israeli team led by Jacob Hanna, comprise all the cell types necessary for an embryo’s development, including the placenta, yolk sac, and chorionic sac. These structures were allowed to develop for eight days, representing a developmental stage equivalent to day 14 of a human embryo in the womb. This stage is crucial as natural embryos acquire the internal structures required for subsequent development of organ progenitors.
Hanna’s team achieved these breakthroughs without using fertilized eggs. Instead, they utilized pluripotent stem cells, derived from adult human skin cells, which possess the potential to transform into various cell types and are widely employed in biomedical research. Consequently, they reprogrammed these cells into a “naïve state” resembling day seven of a natural human embryo. The researchers divided these “naïve” cells into three groups: one group remained unaltered to become the embryo, and the two other groups were subtly manipulated with certain chemicals to induce the development of the tissues necessary for sustaining the embryo.
Although the synthetic human embryo models were initially just clumps of cells, they began to exhibit discernible structure by day four. The structures developed by Hanna’s team, at the equivalent stage of day seven, consisted of approximately 120 cells and measured 0.01 millimeters across. By day 14, they contained roughly 2,500 cells and measured 0.5 millimeters. Hanna and his team maintain that these models faithfully mimic the process through which an early embryo acquires the structures integral to its transformation into a fetus. The organization of these structures corresponds to images found in embryology atlases from the 1960s. Additionally, when secretions from the cells were applied to a commercial pregnancy test, it yielded a positive result.
However, it is essential to note that only 1% of the aggregated cells developed into an embryo-like structure. To maximize the potential of these models as a scientific tool, a significantly higher percentage would be required. Achieving this higher percentage is possible but would likely require several more years of research and development. Peter Rugg-Gunn, a group leader and head of public engagement at the Babraham Institute, expressed optimism about the knowledge that can be gained from these stem cell-based embryo models, pointing out that the current models suffer from low efficiency.
Presently, none of the embryo models have been cultured beyond the equivalent of 14 days, primarily due to the challenges associated with sustaining these structures. The 14-day milestone serves as an important ethical boundary and coincides with the conclusion of permitted lab research on cultured human embryos. This limit was established to address public concerns surrounding test tube babies before in vitro fertilization achieved widespread acceptance, as well as fears regarding the ethical treatment of human embryos. Adopted by numerous countries, the 14-day rule is now internationally recognized as an ethical safeguard.
However, stem cell-based embryo models are not subject to the 14-day limit. The International Society for Stem Cell Research has declared that these models should not be classified as embryos but has stipulated that research involving these models requires ethical oversight. In the future, it might be possible to extend the study of human development beyond the 14-day timeframe using these models, as has already been accomplished with mouse embryo models. Jacob Hanna envisions the potential to explore human embryo development up to 40 days. Nevertheless, Hanna reassures that fears about scientists attempting to replace pregnancy or gestation with these embryo models are unfounded, asserting that such notions belong to the realm of science fiction.
The current embryo models remain rudimentary and exhibit distinct scientific differences from human embryos. They lack the ability to develop into fetuses. Furthermore, guidelines provided by the International Society for Stem Cell Research explicitly prohibit the transfer of any stem cell-based embryo models to a human or animal uterus. Robin Lovell-Badge, a professor and head of the Laboratory of Stem Cell Biology and Developmental Genetics at the Francis Crick Institute in London, emphasizes that these models are not embryos and highlights the importance of forbidding any attempts to implant these structures into a human or animal uterus.
In conclusion, sign up for CNN’s Wonder Theory science newsletter to receive captivating updates on the universe’s wonders. Although the mysteries surrounding human embryo development persist, advances in stem cell research and the creation of embryo-like structures offer immense hope. While challenges remain, these models have the potential to revolutionize scientific understanding in various areas. Respecting established ethical guidelines and conducting research under ethical oversight is paramount to ensure the responsible and beneficial use of these models.
