13/ ⚙️ Mechanistically, AEBP2-L contains a mammalian-specific, disordered N-terminal region with acidic tracts that we find inhibit PRC2 binding to chromatin. Mutations that neutralize this region relieve inhibition and boost H3K27 methyltransferase activity:

12/ Interestingly, across mouse & human tissues, AEBP2-L is the predominant isoform from early embryogenesis, and broadly expressed.

Strikingly, the AEBP2-S isoform, which most labs study, is barely expressed beyond very early development!! 🤯

11/ We next wished to explore PRC2 integrity in the absence of AEBP2 isoforms with @michielvermeulen.bsky.social. We found that while loss of either isoform reduced JARID2 incorporation, JARID2 can associate with PRC2.2 with either isoform or even without both

10/ Indeed, loss of AEBP2-S KO impaired repression of 398 genes normally silenced by PRC2 during differentiation, whereas loss of AEBP2-L did not cause any defect

7/ AEBP2-L acts like a Trithorax group protein! 😲 We found that loss of AEBP2-L, but not AEBP2-S, increases ⬆️ PRC2 binding and H3K27me3 deposition on PcG target genes, mirroring the effect of losing both isoforms

6/ Next, to avoid any potential overexpression issues, we used CRISPR 🧬✂️ to KO either the short, the long or both isoforms in mouse ESCs:

5/ We then confirmed in cells that ectopically expressed AEBP2-L does not binds PcG target genes as well as AEBP2-S. Curiously, ectopic overexpression of AEBP2-L, but not AEBP2-S, reduced overall SUZ12 (PRC2) binding ⬇️⬆️

4/ 🔍We focused on AEBP2, a PRC2 accessory subunit with two isoforms: AEBP2-S (short) and AEBP2-L (long).

Strikingly, we found AEBP2-L inhibits DNA binding by PRC2, whereas AEBP2-S promotes it:

3/ PRC2 is a chromatin repressor complex essential for development and deregulated in disease. While several accessory proteins enhance PRC2, no endogenous inhibitor in somatic cells had been identified — until now! ⚡️

1/ 🚀 AEBP2 isn’t what we thought.

You were told that AEBP2 promotes PRC2 activity on chromatin.

We found the opposite: the most prevalent AEBP2 isoform inhibits PRC2 activity.

👉 surl.li/cgwqcq

A thread 🧵