DNA circles in tumor cells and other cells in the human body? Well, that’s what the guy in the lab coat said…
Human cells are not supposed to have extra bits of DNA floating around, so Mischel described the peculiar substance as extrachromosomal DNA, or ecDNA. He had a hunch that this was not simply some genetic debris and spent the better part of the next decade trying to figure out what that ecDNA was doing in cancer.
The answer turned out to be even weirder than he’d first imagined. Mischel, who is now at the Ludwig Institute for Cancer Research and the University of California San Diego, has since demonstrated that ecDNA carries cancer-promoting genes and that its circular shape fuels aggressive growth streaks and drug resistance. Just last year, he published a photo that clearly shows these circles next to X-shaped chromosomes in a cancer cell.
Today, Mischel is at the center of a small field devoted to studying the circles; it is populated by scientists who, like Mischel, stumbled upon the oddity in the course of their own research…
Some scientists, including Regenberg, are finding DNA circles in seemingly normal cells, although there’s much debate about their importance. These circles are often too small to contain a full gene, whereas ecDNA in cancer is large enough to carry multiple genes tied to tumor growth.
There’s even growing evidence that many organisms use DNA circles as a general strategy to steel themselves against things that should normally kill them. Yeast, the protozoan parasite Leishmania, and weeds all use DNA circles to resist toxic molecules, drugs, and herbicides, respectively, notes Jonathan Houseley, a Babraham Institute geneticist who studies ecDNA in yeast. “Circular DNA keeps popping up whenever we see resistance occurring.”
Ryan Cross, “The curious DNA circles that make treating cancer so hard” at C&EN
Our physics color commentator Rob Sheldon comments,
As you know, bacteria can exchange antibiotic resistance using little circles of DNA called “plasmids”. The plasmid not only carries the anti-biotic resistance gene, but also genes for making little bridges for transferring the plasmid from one bacterium to another. This little toolkit looks designed for horizontal gene transport (HGT), but there wasn’t anything similar to it for eukaryotes.
Then came this article. And apparently humans (a rather sophisticated eukaryote) have circular DNA as well, it just was overlooked for 30 years. And these circular DNA have cancer genes and promoters forming a toolkit, just like bacteria. And the toolkit can be “reintegrated” back into the chromosomal DNA, erupting when necessary.
And that means…
It is a transmissible vector for HGT. In humans. Certified virus-free. And 40% of cancer tumors have this toolkit. Cancer might even be contagious (as it is in Tasmanian devils).
In my mind, this is the death knell for Common Descent.
It should certainly give lectern splinterers headaches.
Rob Sheldon is the author of Genesis: The Long Ascent and The Long Ascent, Volume II