New embryonic cell type that self-destructs to protect the developing fetus discovered

A previously unknown type of cell that self-destructs within days after formation as part of a quality control procedure to protect the growing fetus has been found by researchers looking at gene activity data of the early human embryo. The discoveries shed light on what transpires during the earliest phases of life following fertilization, which may one day aid to enhance IVF or regenerative medicine therapies.

An international team of experts, including those from the University of Bath, found in a recent study that was published on June 20, 2023 in PLoS Biology, suggests that our initial development in the womb may be rather different from what we have previously imagined.

We all began as only one cell, the fertilized egg, even though mature humans are made up of billions of cells. This splits into two cells, which divide into four cells, which divide into eight cells, and so on. The cells eventually begin to specialize in their task. Some will be diverted to form the placenta while others will become the embryo, like trains diverted to various terminal stations.

embryonic cell that self-destructs

A fourth of the cells didn't fit the profile of any of the recognized cell categories (pre-embryo, pre-placenta, etc.), according to analysis of previously published data on gene activity of each individual cell from 5-day-old embryos.

Further research revealed that these cells possessed what are known as "Young transposable elements" or "jumping genes." These are renegade DNA components that may replicate and re-insert themselves into human DNA, frequently causing harm in the process.

The presence of the cells with proteins resulting from the jumping genes was established by staining of embryos by project colleagues in Spain.

A bit later along in time, the scientists discovered that their offspring experience both DNA damage and programmed cell death.

quality assurance procedure

The researchers hypothesize that this mechanism resembles a type of quality control, selecting cells in favor of the best.

Dr. Zsuzsanna Izsvák, co-senior author and an authority on mobile DNA at the Max Delbrück Center, stated: "Humans, like other species, engage in a never-ending cat-and-mouse game with these hazardous jumping genes.

"While we make every effort to inhibit these jumping genes, they remain active in some cells very early in development, perhaps because our genetic defenses cannot evolve quickly enough."

Professor Laurence Hurst, co-lead author and director of the Milner Centre for Evolution at the University of Bath, said: "The embryo is better off removing these cells and not allowing them to become part of the developing baby if a cell is damaged by the jumping genes or any other type of error such as having too few or too many chromosomes.

Natural selection is understood to favor certain organisms over others. The survival of the fittest appears to be taking place within embryos as well, although this time amongst almost identical cells. It appears that we have discovered a new weapon in our armory to combat these dangerous genetic components.

Professor Laurence Hurst, Milner Centre for Evolution at the University of Bath, is a co-lead author.

fighting new genetic threats with old genetic foes

Contrarily, the single-cell data revealed that the inner cell mass, or ICM, or the crucial cells that will develop into the embryo, do not include jumping genes but rather express a virus-like gene known as human endogenous virus H. This supports a developing pattern in which we deploy our old genetic foes to battle our new ones, which helps suppress the youthful jumping genes in the inner cell mass.

The authors contend that an overly sensitive quality control procedure might result in the death of the entire embryo. This may help to explain why some abnormalities that affect our ability to recognize harm to developing embryos are also linked to infertility.