Thursday, September 28, 2006

More Syncytia Sweetness

Syncytia formation is a fun technique I use in the lab to see if the viruses Ive made are infectious. But theyre important in vivo too— you wouldn’t be alive without retroviruses and their syncytia trick.

During embryological development, your first cells made a viral protein. No, you cant use ‘early embryological viral infection’ as an excuse for why youre so messed up. A functional viral env gene is in all of our genomes, and its still there right now. But this endogenous retrovirus is only actively transcribed and translated in embryos—Its env is expressed on the surface of embryo cells, and they use the syncytia trick to build you a placenta! When experimenters used siRNA ** to knock down this endogenous retrovirus, the embryo freaks out and wont make a placenta!

Its not exactly *ethical* to try this on a real baby—so the same group that found this ERV looked in mice to see if they could find something similar. They did! Another group found an ERV with the same function in sheep! The sheep guys went so far as to knockdown the expression of the sheep embryo ERV in actual embryos in a mommy sheep… and the embryos died. So that pretty much clenches the fact we need this endogenous retrovirus to survive.

Okay, so that makes sense. All mammals need placentas, I bet this retrovirus helped us ‘kingdomate.’ Not quite—this gets weirder. So far we know humans, mice, and sheep have ERVs that perform the same function… but all of them are different! Syncytin-1 and Syncytin-2 in humans are different from Syncytin-A and Syncytin-B in mice, which are different from enJSRV in sheep! Each of these species independently acquired a retrovirus that became endogenous and performs the same function! Kinda like how ‘eyes’ all perform similar functions, but eyes independently evolved at least 40-60 times! Or how bats and birds and insects have wings, but they all evolved them a different way! Convergent evolution!!

We don’t have the whole story on the origin of these ERVs, or whether there was a common mammalian embryo ERV that got replaced by ‘better’ embryo ERVs in each species over the course of time… I love it when we find tips of icebergs!






**(Instead of finding out what a gene does by irreversibly screwing it up and seeing what happens to the cell, siRNA lets you just make the gene shut up for a minute, you can see what happens when the gene isn’t translated. When the siRNA gets degraded, the gene gets expressed again and you can watch what happens then.)

Human paper

Mouse paper

Sheep paper

2 comments:

charles said...

Convergent evolution looks suspiciously like tautologous dogma. Felids, nimravids, and marsupial thymacosmilids (all cat lines) have each produced sabertooth cats independently. Haem and myoglobin have very similar tertiary and quaternary sturctures but very different primary sequences and codes. At least three different ERVs, different gene sets, different promoters and different placental structures (http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.cellbio.24.110707.175418 (requires subscription))- is improbable neo-Darwinist selection really crafting these parallels or is this just paradigm blinker?

My post is partly a test to your filters, SA, and partly enquiry.

ERV said...

If this is Charles Jackson:
1-- This blog has been closed for about a year now. High-five on observational skills there, Chet.
2-- You honestly expect me to allow you to post on *my* blog, while you censor comments at YouTube? Pussy. Pathetic little pussy.
3-- wtf does this comment have to do with the OP? Really? This is the post you randomly choose to comment on? The one that has absolutely nothing to do with ERVs? Not 'Creationist Claims About ERVs' prominently listed in my side-bar? LOL!

You are more than welcome to post at New ERV, if your delicate ego can handle it.

If this isnt Charles Jackson, please disregard #2, but #1 and #3 are still applicable.