Weird science fact of the day:
Girl birds only have a left ovary. The right one kinda develops, and then regresses. Left ovary is the only one that works. All birds.
What the hell?
What kind of evolutionary weirdness led to this absurdity?
I bet you guessed an ERV is involved
OVEX1, a novel chicken endogenous retrovirus with sex-specific and left-right asymmetrical expression in gonads.
For real, you all should download and read over this one. Its in obnoxious ‘pre-print’ format (ie almost unreadable format. figures, figure legends, and text about figure all on different pages– double spaced– it sucks), but I swear its worth it. This paper is wonderfully descriptive, refreshingly down-to-earth, and touches on just about everything you guys already ‘get’ about ERVs and evolution.
So heres the deal: birds have lopsided gonads. WTF. So there have got to be some gene expression differences between left/right gonad to tell the left to keep going, and right to shut down. So these folks played some RNA tricks to see what message RNA was being made in chicken gonads during development, left vs right (its easier to look for unknown RNA than it is to look for unknown proteins, which would actually be more relevant, but this is a good place to start).
So what was an interesting mRNA difference between left/right gonads? A previously ‘undiscovered’ ERV, Ovex1. Ovex1s closest relative in the real world? Another ERV in tuataras. Lizards. WTF LOL! RNA from Ovex1 could be found in both gonads initially, but it trails off in the right, and spikes in the left, along with follicular granulosa differentiation and development.
Ovex1 expression highlights striking desquamation process that leads to profound cortical remodeling associated with follicle morphogenesis.
Now, these researchers are not IDiots like Casey Luskin. They understand that sometimes, transcripts are just junk. So they make this important disclaimer:
To speculate further about the function of Ovex1 (and FET-1) in the ovary, it would be necessary first to establish whether the encoded proteins are actually translated…
… The future objective will be to determine if it (Ovex1) is only witness or if it is an actor.
Just because RNA is made, doesnt mean proteins are made. Sometimes RNA just happens. And cells have lots of tricks for shutting down unwanted RNA before they can make protein. All biologists know this, which kinda explains why Casey doesnt. But before you laugh too hard at Casey, remember that there are many scientists who would have left out these statements, instead choosing to declare that transcription of this ERV is why chickens have lopsided gonads.
So kudos to these folks!
But even though they readily admit that their detection of RNA from this ERV at this particular stage in development could be nothing, they dont think it is.
However, conservation of the ORFs suggests the existence of selection pressure acting to retain not only the RNA but also the encoded proteins.
Even though they found Ovex1 in chickens, they also find it in Zebra Finches, which, according to The TimeTree of Life, diverged from chickens about 100 million years ago.
These species diverged ~100 mya, and yet this ERV has ~83% sequence similarity between the two, and it is located on the same chromosome (#4), between the same two genes (CD8 and SMYD1).
They also found Ovex1 in turkeys and duckies and guinea fowl. If you make a phylogenetic tree with everyones Ovex1, and compare it to standard birdie phylogenies, they match up perfectly. lol.
And while the env genes have gone to hell (OMG JUNK DNA! JUUUNK DNAAAAAA!), parts of the gag gene are pretty damn well conserved between all these species. Like, 100% amino acid homology. Ya. As are parts of pol.
I think its funny that so many RNA fishing expedition papers– I dont believe their declarations until they show me some proteins and some basic gain-of-function/loss-of-function experiments. The folks on this paper didnt make any extravagant claims, but I believe them without protein data because, well, evolution kinda made their case for them. You dont keep an ERV around with 100% aa homology for over 100 million years just cause you like having eye candy around.
Ovex1 isnt the reason for lopsided bird ovaries, but theyre playing a role in it… Like winning a role in a John Waters movie…