New study busts long-held myths about human embryo development

A new study from Caltech, published in the December 3 issue of the journal Cell, revealed a specialized asymmetry between the two cells of fertilized human beings in their earliest stages of development, disproving the previous assumption that the cells of embryos only serve specific roles later in development.

Key Takeaways:

• A new study published in the journal Cell has revealed that the first two cells in an embryo are significantly different from one another. Previously, they were believed to be the same.

• Using mouse embryos to study the first moments of life after fertilization, researchers found that asymmetries exist between the two cells (blastomeres) of the two-cell embryo.

• It was previously thought that sperm only provided genetic material, but the study revealed that the entry point of the sperm determines which of the two cells will lead to the formation of the embryo's body. The other will make up the placenta.

• After studying the two-cell mouse embryos, researchers moved their research to two-cell human embryos and had similar findings.

The Details:

Using mouse embryos composed of just two cells right after their first cellular division, researchers in Biology and Biological Engineering professor Magdalena Zernicka-Goetz's lab were able to find that the two cells differ from each other significantly.

"It was previously assumed that all of the cells of a developing embryo are identical, at least prior to the stage when the embryo consists of 16 or more cells," reported Pasadena Now. "But the new study shows that differences, or asymmetries, exist even in both cells of a two-cell-stage embryo. These differences enable the specialization of the cells—in this case, leading to the formation of the body and the placenta. At this stage, the cells of the embryo are called blastomeres" (emphasis added).

The study notes, "... mammalian development has long been thought to begin with equivalent blastomeres. However, emerging evidence challenges this."

In addition, the study found that the location at which the sperm enters the egg is a major factor in determining which blastomere will play which role. It has long been thought that sperm simply provides genetic material; however, this study found that where the sperm enters sends a vital signal to the embryo.

"Importantly, the research reveals that the cell that retains the site of sperm entry after division will ultimately make up the majority of the developing body, while the other largely contributes to the placenta," reported the Pasadena News.

Zoom In:

According to the study, "Moreover, splitting 2-cell embryos into monozygotic 'half embryos' reveals that while one blastomere can generate a viable embryo, the other typically cannot."

In addition, researchers found 349 proteins distributed asymmetrically between the two cells, "implicating fertilization as a symmetry-breaking event."

In one cell, certain proteins were overproduced; in the other, they were deficient. Each of the proteins is important to the process of building and degrading other proteins because the number of proteins supplied by the mother declines, and they are replaced by proteins created by the embryo.

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What's Happening:

Tragically, the researchers took those findings and used them to conduct research on human embryos.

The study said, "Due to the scarcity of human embryos, our sample size was necessarily smaller than in mice...." It continued, "[W]e found that sister blastomeres from human 2-cell embryos reliably segregated into two distinct clusters" and "correlation analysis showed that the two human clusters aligned closely with the mouse alpha and beta profiles..."

In comparing results between two-cell mouse embryos and two-cell human embryos, researchers found that "although the core biological processes are conserved, species-specific regulatory differences exist for individual proteins."

The Bottom Line:

Embryos are unique persons, and are each individual human beings at the moment of fertilization — the start of their existence — who will continue to grow and change from embryo to fetus to infant to toddler and so on.

Rather than respect their intrinsic value and their dignity, human beings were experimented on in this study and died as a result of it. Furthermore, the researchers hope it will lead to constructing new ways to determine the viability of embryos created through in vitro fertilization (IVF), potentially leading to further destruction of human lives by expanding embryonic testing in IVF labs.