Every cell carries a set of instructions, its genes, that tell it how to operate. But among those instructions are mobile elements that can copy themselves and insert into new spots. One of them, LINE-1, makes up about 17% of our DNA. Scientists set out to test what happens if this element is forced to work too actively in healthy cells.
They took connective tissue cells and introduced a full-length LINE-1 into them. Three days later, they measured which genes had switched on, which proteins had appeared inside the cell, and what the cell had begun to release outward. It turned out that the activity of more than a thousand genes had changed: some became more active, others fell silent. The cell started dividing faster, while its defense system, which normally responds to viruses, quieted down instead.
Previously, scientists did not know whether LINE-1 activation was a cause of aging or merely a consequence. Now it is clear that this element can rewire the cell on its own, like a conductor who changes the orchestra's score. These findings will help study aging, inflammation, and cancer, and also to test drugs that block reverse transcriptase, the enzyme LINE-1 needs in order to copy itself.
LINE-1 accounts for about 17% of the human genome, but only a small fraction of copies are capable of moving. In the experiment, after transfection only 6–10% of HEK293T cells became GFP-positive, reflecting the rarity of successful retrotransposition.
In Greg Bear's novel "Blood Music," mobile genetic elements reshape human biology. Here L1 does something similar, but on the scale of a single cell, rewriting its programs without changing the DNA sequence.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.