A recent study shows that a one-day-old early human embryo consists of two seemingly identical cells, but in fact, one of the cells contributes more to the body's organs and tissues. This finding may help improve the success rate of in vitro fertilization (IVF) procedures.
The study, published in the journal Cell, reveals that the first division of the fertilized egg causes subsequent cells to tend toward different fates, thereby laying the foundation for development into a complex fetus. Developmental biologist Ali Brivanlou of Rockefeller University in New York City called the study "a major step forward" and said that as the research progresses, its clinical significance will become more apparent.
The Origin of Asymmetry
For a long time, researchers believed that when mammalian fertilized eggs had fewer than 16 cells, all cells were identical and did not begin to differentiate until later stages of development. After all, a fertilized egg that splits into two separate embryos after a few cell divisions can still form identical twins.
However, in 2001, developmental biologist Magdalena Zernicka-Goetz of the California Institute of Technology pointed out in a paper that the first two cells of a mouse embryo are actually different. One cell mainly forms the fetus, while the descendants of the other cell mainly form the yolk sac.
A Long-Term Study
Zernicka-Goetz had long wondered whether the same phenomenon exists in humans. She obtained 54 fertilized eggs that had not yet completed their first division from an IVF clinic. The researchers allowed these fertilized eggs to divide in the laboratory and labeled one of the embryonic mother cells with a fluorescent protein, thereby tracking the development of the descendants of each cell.
After four to five days of culture, these embryos began to form different structures. Analysis showed that most of the cells in the structures forming the fetus came from the faster-dividing embryonic mother cell, while the descendants of the slower-dividing cell mainly transformed into the yolk sac.
Brivanlou was astonished by this degree of asymmetry but considered it logical, because the human body ultimately becomes extremely complex. "The deeper we delve, the more we realize that life is composed of successive symmetry breakings," he said.
The Cause of Asymmetric Development
It is still unclear what causes this asymmetry. In mice, the location where the sperm enters the egg affects how the egg divides, and Zernicka-Goetz believes that other factors, such as the structure of chromosomes in the egg, may also influence this balance.
Understanding which cells are more likely to form the fetus may enable IVF clinics to better screen embryos to find those most likely to result in a successful pregnancy. "If we can understand the vulnerabilities of this period, some miscarriages could be avoided," she said. Although it is difficult to predict how this early asymmetry affects the later human body, the impact could be very long-lasting.
Author LinkedIVF TeamPublished 2024-05-15
This article used AI assistance; LinkedIVF has not recorded an editorial review for this item. It is not medical advice.
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News | Scientific Breakthrough: Human Embryos Form the Body Through Asymmetric Cell Division
A recent study shows that a one-day-old early human embryo consists of two seemingly identical cells, but in fact, one of the cells contributes more to the body's organs and tissues. This finding may help improve the success rate of in vitro fertilization (IVF) procedures.
The study, published in the journal Cell, reveals that the first division of the fertilized egg causes subsequent cells to tend toward different fates, thereby laying the foundation for development into a complex fetus. Developmental biologist Ali Brivanlou of Rockefeller University in New York City called the study "a major step forward" and said that as the research progresses, its clinical significance will become more apparent.
The Origin of Asymmetry
For a long time, researchers believed that when mammalian fertilized eggs had fewer than 16 cells, all cells were identical and did not begin to differentiate until later stages of development. After all, a fertilized egg that splits into two separate embryos after a few cell divisions can still form identical twins.
However, in 2001, developmental biologist Magdalena Zernicka-Goetz of the California Institute of Technology pointed out in a paper that the first two cells of a mouse embryo are actually different. One cell mainly forms the fetus, while the descendants of the other cell mainly form the yolk sac.
A Long-Term Study
Zernicka-Goetz had long wondered whether the same phenomenon exists in humans. She obtained 54 fertilized eggs that had not yet completed their first division from an IVF clinic. The researchers allowed these fertilized eggs to divide in the laboratory and labeled one of the embryonic mother cells with a fluorescent protein, thereby tracking the development of the descendants of each cell.
After four to five days of culture, these embryos began to form different structures. Analysis showed that most of the cells in the structures forming the fetus came from the faster-dividing embryonic mother cell, while the descendants of the slower-dividing cell mainly transformed into the yolk sac.
Brivanlou was astonished by this degree of asymmetry but considered it logical, because the human body ultimately becomes extremely complex. "The deeper we delve, the more we realize that life is composed of successive symmetry breakings," he said.
The Cause of Asymmetric Development
It is still unclear what causes this asymmetry. In mice, the location where the sperm enters the egg affects how the egg divides, and Zernicka-Goetz believes that other factors, such as the structure of chromosomes in the egg, may also influence this balance.
Understanding which cells are more likely to form the fetus may enable IVF clinics to better screen embryos to find those most likely to result in a successful pregnancy. "If we can understand the vulnerabilities of this period, some miscarriages could be avoided," she said. Although it is difficult to predict how this early asymmetry affects the later human body, the impact could be very long-lasting.