Invasion of genomic parasites triggered modern mammalian pregnancy

Genetic parasites invaded the mammalian genome more than 100 million years ago and dramatically changed the way mammals reproduce -- transforming the uterus in the ancestors of humans and other mammals from the production of eggs to a nurturing home for developing young, a new Yale University study has found.

The findings published online Sept. 25 in the journal Nature Genetics describe in unprecedented detail the that allowed mammals to carry their developing young within the safety of the womb rather than laying them in nests or carrying them around in pouches.

"In the last two decades there have been dramatic changes in our understanding of how evolution works," said Gunter Wagner, the Alison Richard Professor of Ecology and (EEB) and senior author of the paper. "We used to believe that changes only took place through small mutations in our DNA that accumulated over time. But in this case we found a huge cut-and-paste operation that altered wide areas of the genome to create large-scale morphological change."

The Yale team studying the of pregnancy looked at cells found in the uterus associated with placental development. They compared the genetic make-up of these cells in — marsupials that give birth two weeks after conception — to armadillos and humans, distantly related mammals with highly developed placentas that nurture developing fetuses for nine months.

They found more than 1500 genes that were expressed in the uterus solely in the placental . Intriguingly, note the researchers, the expression of these genes in the uterus is coordinated by transposons — essentially selfish pieces of genetic material that replicate within the host genome and used to be called junk DNA.

"Transposons grow like parasites that have invaded the body, multiplying and taking up space in the genome," said Vincent J. Lynch, research scientist in EEB and lead author of the paper.

But they also activate or repress genes related to pregnancy, he said.

"These transposons are not genes that underwent small changes over long periods of time and eventually grew into their new role during pregnancy," Lynch said. "They are more like prefabricated regulatory units that install themselves into a host , which then recycles them to carry out entirely new functions like facilitating maternal-fetal communication" Lynch said.

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Sep 25, 2011
Sounds plausible, I always wondered how evolution would let a species evolve where giving birth was such a huge mortal risk to the maternal parent. I mean birthing mothers had a huge mortality rate due to infection and this was only remedied with modern antibiotics.

Sep 25, 2011
OK, where does the complex information come from for the transposon to be able to do something as sophisticated as this?

Sep 25, 2011
you know, sometimes i wonder if evidence of extra terrestrial enhancement isnt just staring us in the face.

Sep 26, 2011
OK, where does the complex information come from for the transposon to be able to do something as sophisticated as this?

You're asking the wrong question. What you should be asking is "how do these complex transposons arise?"

Of course the answer, as always, is "evolution". We've known about it for quite a long time now, I'm surprised you weren't taught about it in school. I'd recommend taking a look at wikipedia, as they have some very detailed articles on this process and how it works.

It's actually one of those "amazingly obvious" things that you get in science, where it hides right under your nose, but as soon as you see it once, you see it everywhere. Trust me, you'll love it.

Sep 26, 2011
A bit too much sensationalizing, a bit too few explanations. In the article, not in the research.

The article is rather misleading in title and content when compared to the research as well.

Sep 26, 2011
This's deeply shocking stuff.

Stuff we're told's junk somehow transforms a body's few day egg building structures into an environment where shell-less life can be sustained AND developed for months on end.

That's a bit like finding out the rust making your car fall to bits somehow's turned it into technology capable of growing to term a week old human foetus over nine months.

The reason it's referred to as "selfish" or "parasite-like" is because it's assumed it's something like a bank robber holding DNA hostage to keep itself alive: yet how many bank robbers - or parasites of any kind - know how to rearrange the 'bank' so it can keep alive the week old foetus the teller's just aborted.

Even now, if we tried to genetically manipulate chicken DNA to make them internally sustain and build chicks into young hens all we'd succeed in doing is make them abort.

So how's that even remotely possible for 'junk'?

And people guffawed at the 'science' in John Carpenter's The Thing...

Sep 26, 2011
alanborky: Remember that this 'junk DNA' has newer been junk. It was at some point named as junk, because at that time there was no knowledge what it was for. Now when we know more about genomics, it has proven that there are meaningful uses for this DNA stuff.

Sep 26, 2011
Wonder if we could eventually get animals that lay eggs to give birth instead or vice versa.

"Why would would you want to do that?" you ask? Why not?

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