Thanks Eric!

Thanks Jay!

Thanks a lot Josh!

Together, our data show that Rtl1 is an essential mRNA cleavage target of AGO2 and suggest that the repurposing of a retrotransposon-Argonaute regulatory interaction contributed to the retention of AGO catalytic competence in mammals

And finally, if we restore silencing of Rtl1 in mutant endothelial cells, we can essentially rescue all the endothelial phenotypes we documented!

It is also an imprinted gene, expressed only from the paternal allele. The maternal allele expresses instead a cluster of miRNAs that overlap Rtl1 in an antisense manner.

And you guessed it: we can find Rtl1 cleavage products for these miRNAs in RNA from wild-type but not catalytic mutant animals

Who is Rtl1? It turns out it is a domesticated retrotransposon known to regulate endothelial cell function - these are the cells that line our vessels

Turns out that one of the up-regulated genes, Rtl1, has 10 (!!!) perfect binding sites for well-expressed miRNAs! 😱

This extent of complementarity is well known to trigger RNA cleavage by AGO2

This is also pretty obvious in expression profiles from these animals, which show numerous genes up-regulated, which are largely involved vasculature development

It turns out, there a lot more wrong with these animals than just anemia (check out the paper for all the things we found!)

For one thing, these animals have extensive vascular defects characterized by enlarged and leaky vessels

So clearly there are other important cleavage targets in mammals.

We set out to find who they were!

These are so far the only cleavage targets in mammals whose dysregulation was shown to cause phenotypes in AGO2 catalytic dead mice - a very strong anemia

And yet.... these animals also die a few hours after birth! For unknown reasons!

we know from work in the Hannon and @lucksmith.bsky.social's labs that that AGO2 slicing is required for erythrocyte differentiation by promoting the maturation of 2 unusual miRNAs:

pubmed.ncbi.nlm.nih.gov/20424607/
pubmed.ncbi.nlm.nih.gov/29351846/

It is fair to say that we have been obsessed with mammalian Argonaute proteins in the lab, and particularly the ability of AGO2 to slice transcripts!

This activity is incredibly conserved, and yet we have a poor understanding of what it's regulatory functions are in mammals 🤔

Learn more about her work on piRNAs here: www.niddk.nih.gov/about-niddk/...

Our final speaker of the day is Astrid Haase, who will tell us about RNA-guided genome protection

Learn more about Katie’s work on miRNAs here: www.niddk.nih.gov/about-niddk/...

Next speaker is Katie McJunkin who will tell us about the developmentally timed decay of an essential miRNA family