Sci Am, Wired, ScienceNow, Ph.Inquirer: Ebola, Marburg, other viruses are built into us. Sort of, for millions of years.
In the Public Library of Science (PLoS) Pathogens this week researchers from the Institute for Advanced Study in New Jersey and Philadelphia’s Fox Chase Cancer Center report finding a slew of viral, RNA-based genome sequences in a long list of vertebrates. That includes people. Among the most common are snippets put into our ancestors millions of years ago by relatives of today’s dangerous Ebola and Marburg viruses.
What’s important is that these are not leftovers from retroviruses that naturally insert DNA copies of their genes into hosts’s genomes, thus indirectly hijacking cells’ ribosomes to manufacture more viruses. These are genes from viruses that send messages directly to that machinery. Exctly how these viruses got partly encoded into vertebrate genomes is, researchers say, a matter for speculation. The paper triggered wide pickup, particularly in specialty press devoted to the more arcane discoveries in science, but also some in more general media. The paper, and the news articles I’ve seen, still leave me puzzled in some respects, which I’ll get to.
Stories:
- Wired News – Brandom Keim: Genome Surprise: Guinea Pigs Have Ebola! ;
- AAAS ScienceNow – Jennifer Couzin-Frankel: Deadly Viruses Have Been Part of Us for Millions of Years ;
- Scientific American – Katherine Harmon: Genes from Ebola Virus Family Found in Human Genome ;
- Science Friday – Ira Flatow (with an author of the study): The Virus in Your Genes ;
- Philadelphia Inquirer – Tom Avril: Study of virus fossils offer clues to surviving infections ;
My Confusion: These stories cover much that is easily understood and significant, such as that these insertions and their persistence for 40 million years may mean they endow hosts with resistance to associated diseases. And, the sheer weirdness of it is news. But…what exactly seems to have happened? All the stories I saw say the insertions may have occurred as long as, again and as the press release says, 40 million years ago. How they can tell that, I don’t know, but it has something to do with mutation rates and comparisons between closely related species. Still, is it supposed that these viruses all, separately, got into vertebrate lines as distantly related as bats, humans, squirrels, mice, guinea pigs, shrews, and others within that span? It seems from here that the wonder is not that it happened so long ago, but that it was so recent in evolutionary time. Yet these viral scraps are so near-ubiquitous. Common ancestors to all these vertebrates go much farther back than 40 million years. Plus, why the fuss over the viral clan including Marburg and Ebola? Some stories say humans carry Ebola’s ancient baggage (Avril’s at the Inquirer, by the way, says explicitly we don’t have those – but do from another type of virus). They belong to this larger family of viruses that did much of the infiltrating, but is there reason to think it was actual Ebola etc. doing it? And if it only happened in the last 40 million years, was there a big burst of viral invasions so many hundreds of millions after viruses and vertebrates arose? Am I missing something obvious to all the other writers who actually reported this story?
I get why it’s interesting. Such as, that the fossil viral genomes in vertebrates may be a better clue to viral evolution than the genes of today, rapidly-adapting viral descendants. But the prehistoric narrative eludes me. Maybe Ira Flatow asked about this on his Science Friday show today, too late on the air for me to listen to it.And the paper itself is very long – so haven’t had time to wade through it.
- Charlie Petit
Grist for the Mill:
PLoS Pathogens Paper ; Fox Chase Cancer Center (Phila) Press Release ;
Pic source ;
- Charlie Petit
