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A ‘Parasite’ Jumping Gene Turns Out To Be Critical For Embryo’s Survival

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Experts have long considered the "jumping gene" or "transposons" as either parasitic element or useless genetic material despite comprising practically half of the humans' DNA.

Before anyone else becomes an actual human being, they needed to pass the critical stage of being a two-celled embryo. A new study now finds that a type of the so-called jumping gene, which scientists have always set aside as a trash item in the human DNA, is integral to that early stages of embryonic development.

The Paradox

About 50 percent of the human's DNA is made up of the transposons. The problem with this jumping gene is that it inserts itself virtually everywhere in the human DNA by copying or replicating themselves. They act like a virus, and most of the times they can cause a mutation to cells that later on develop into cancer.

The most common type of the jumping gene is the "LINE1." It comprises 17 percent of the human's DNA.

For LINE1 to replicate, it first produces an RNA version of itself. An enzyme will then transform this RNA back into DNA as soon as it reaches a place in the genome. At this stage, the replication process could have possibly damaged the mutated DNA. Later on, this mutation in LINE1 can lead to cancer or more specific genetic disorders such as hemophilia.

This is how dangerous LINE1 works. However, as risky as this gene sounds, LINE1 actually moves around generously during the early embryonic development.

While cells will normally restrain LINE1, as it does to all transposons, the early embryonic cells actually allow them to roam free. Hence, embryonic stem cells and early embryos are found to have high levels of LINE1.

For Miguel Ramalho-Santos, the senior author for the study and an associate professor at the University of California San Francisco, the pleasant response of embryonic cells to LINE1 seemed to be paradoxical.

"Given the standard view of transposons, these early embryos were really playing with fire. It just didn't make any sense," said Ramalho-Santos.

Solving The Paradox

Ramalho-Santos, together with Michelle Percharde, a Ph.D. from the university, decided to solve this paradox both thinking that LINE1 may actually be beneficial to the embryonic cells rather than being parasitic.

For their study, published in the journal Cell on June 21, the researchers designed small molecules that can reduce the amount of LINE1 in cells by 80 to 90 percent. They applied this method and constrained LINE1 in mouse embryonic stem cells. The experiment showed that removal of LINE1 RNA dramatically reduced the cell's ability to replenish themselves.

The experiment also showed that when LINE1 RNA was constrained and insufficient, the mouse embryos also failed to successfully pass through the two-cell stage. If the embryo failed to progress way pass the two-cell stage, then an offspring will not develop at all. This process holds true as well for human's embryonic development.

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