Ancient virus may be protecting the human placenta | Hacker News Reader

Ancient virus may be protecting the human placenta

science.org

50 pointsVigier19 comments

This is not my field and my understanding of it is limited to high school science, but a picture being painted for me as a naive consumer of scientific news is that we're seeing evidence that viruses are playing a role in evolution. We get infected with things that alter our DNA, and sometimes those alterations give us advantages.

It leads me to wonder if there's a role mosquitos play in our ecosystem after all. It's long held that mosquitos serve no positive purpose in ecosystems and ought to be eradicated when possible. When confronting the affects of malaria, it's hard to argue against the idea, but it's certainly true that mosquitos are an effective virus delivery mechanism. If sometimes viruses play to our advantage, maybe there's more to the insect's role.

Or maybe I just need to read more.

> mosquitos serve no positive purpose in ecosystems and ought to be eradicated when possible

I've heard the same, but it really feels like a naïve take. We can't know for sure that they have no positive purpose in their ecosystems, and eradicating them is a one way street.

No idea where the belief came from, but it's a bit concerning how widely held it is.

This is, of course, the counterargument to eradication, which is what leads me to muse on it

As I've read it, it's always regarding the food chain. I've never seen a paper that said mosquitos were completely inconsequential, just that if they were completely removed, the food chain wouldn't be damaged.

Somewhat tangentially, a mosquito eradication effort increased the rates of Dengue hemorrhagic fever - the opposite of what was intended.

With Dengue, if the body is exposed to multiple strains within a short time period, there's no severe reaction.

However, if there's a delay, and the body gets to prepare, and then sees a slightly different Dengue virus, the shit hits the fan.

So the decreased number of mosquitos left a greater mean time between cross-strain exposure, which in turn increased the number of severe reactions.

That's not a argument against mosquito eradication, though; that's a argument against not finishing a mosquito eradication.

No, it's an argument against partial mosquito eradication - which is an intermediate step for complete eradication.

Is this what you're trying to cite?

If so.... the resurgence in populations is what caused the increase.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3516305/

I'm not sure, but my recollection of the article in question is quite specific - that when there was a delay between exposures across strains, the hemorrhagic fever did not result.

This article (The Autoimmune Mechanism in Dengue Hemorrhagic Fever) https://pubmed.ncbi.nlm.nih.gov/29686179/ is probably more relevant.

Why cross-strain exposure would prevent that auto-immune reaction, I have no idea - probably something to do with tiny little puzzle pieces that almost fit.

(And no real need for the condescension.)

Does anybody know if there is a less vague date than "millions of years ago" as to when this retrovirus started becoming apart of human DNA? Were we even humans at the moment?

I listened to a podcast on this and they said it allowed the placenta to evolve in the first place. That's what I remember. Anyone else?

I've read it in some pop sci book on genetics as well that without retroviruses we wouldn't have placental mammals, it's certainly convincing theory given how weirdly these cells need to behave.

If you can find the source for that I’d love to read about it

I read this theory in The Mom Gene but I'm not sure where it sourced from.

https://whyy.org/segments/the-placenta-went-viral-and-protom...

https://www.pbs.org/wgbh/nova/article/endogenous-retroviruse...

From the NOVA episode which gets to the human related part, (but that whyy article is on the protomammal rather than primate and thus may be of more interest to you).

> All was going as planned until McCoy’s bioinformatics specialist Steve Howes rushed into his lab in 1997 to show him the sequence of a gene they called syncytin, which their work showed was secreted by placenta tissue.

> Before McCoy could go public with his discovery, he needed to figure out exactly what syncytin did, a job he passed to bench scientist Sha Mi, who everyone called Misha. Misha’s experiments seemed to be going as planned until, a few months later, she, too, rushed into McCoy’s lab with findings of her own.

> Syncytin is produced only by certain cells in the placenta, and it directs the formation of the cellular boundary between the placenta and maternal tissue. Approximately one week after fertilization, the egg, now a hollow ball of cells called a blastocyst, implants itself into the uterus, stimulating the formation of the placenta, which provides the fetus with oxygen and nutrients while removing carbon dioxide and other wastes. It also serves as a barrier to prevent infection and keep maternal and fetal blood separate. (Mixing the two could cause a fatal autoimmune response.) The cells in the outer layer of the blastocyst form the outer layer of the placenta, and those in direct contact with the uterus are the only ones that made syncytin.

---

This then links to

Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis https://www.nature.com/articles/35001608

Retroviruses push the envelope for mammalian placentation https://www.pnas.org/doi/full/10.1073/pnas.1121365109

Also the wikipedia page on it: https://en.wikipedia.org/wiki/Syncytin-1 (and all the references that one finds in a science related wikipedia article)

primates aren't the only placental mammals though

> About 30 million years ago, a virus infected our primate ancestors and one of its genes got trapped in their genomes.

So at +/- 1 million, that's a range of 29-31 million, or three million years. That still seems imprecise, to be fair.

For any virologists out there, is this question similar to estimating the date of a Git commit? Or maybe it's similar to finding the nearest tag to a given commit, where a "tag" is some external reference point with a known date (like a fossil or ice core)?

Literally the first line of the article.

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