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A #tweetorial from @RossLevineLab and colleagues on our new preprint online today at @biorxivpreprint from @sloan_kettering biorxiv.org/content/10.110…
1. The cohesin complex is comprised of structural proteins (Smc1a, Smc3, Rad21) bound to a Stag protein (most commonly Stag1 or Stag2). The entire complex is targeted by somatic mutations in myeloid malignancies, whereas STAG2 is most prevalent across all cancer @cohesin_papers
2. We & others have described that the core cohesin complex regulates hematopoietic self renewal & differentiation. However the fundamental biologic mechanism remained unclear & the unique role of Stag2 in gene regulation, hematopoiesis & transformation was not known.
3. How does the cohesin complex affect @3D_Genome DNA structure and how does this affect @generegulation ? How do alterations in Stag2 impact the balance between self-renewal and differentiation?
4. How is Stag2 and its role in gene regulation and tumor suppression different than that of the core cohesin complex members?
5. Using novel conditional KO mice (now available @jacksonlab), we show increased self-renewal and altered differentiation (myeloid, B cell) with Stag2 loss, but not w Stag1 loss. Dual Stag2/Stag1 loss is synthetic lethal in vivo (shown by @johannes_zuber and colleagues in vitro)
6. This suggests Stag1 redundancy must maintain viability, but cannot function in tumor suppression in the absence of Stag2. Moreover Stag1 is dispensable in somatic cells in contrast to developmental lethality in embryonic cells (@analosada)
7. ChIPseq for Stag2 and Stag1 in HSPC of WT and Stag2 KO mice showed Stag2/Stag1 co-bound and Stag2-unique binding sites. Stag1 was able to bind TAD boundaries. Hi-C in primary stem/progenitor cells confirmed that TADs were NOT altered by Stag2 loss
8. With Stag2 loss, genes with decreased expression and decreased ATAC accessibility lose short range DNA-DNA interactions by HiC (10kB resolution), including key B cell lineage commitment genes. @ArimaGenomics @SwiftBioSci @loops_enhancers @EpigenChromatin
9. But does failed expression of these genes lead to alterations in DNA interactions or do DNA structural changes impair transcriptional programming and the ability of upstream @AllAboutTFs to turn on their targets?
10. The PU.1-target, Ebf1, loses insulation, accessibility, and expression. As PU.1 is a putative pioneer factor, it has the capacity to remodel chromatin. However, PU.1 expression was unable to restore Ebf1 expression
11. This illustrates that changes in local interactions are the cause of abnormal gene expression. In contrast to PU.1 expression, Ebf1 expression rescues lymphoid lineage commitment and B cell colony formation and attenuates self-renewal of Stag2 deficient cells
12. Hematopoietic differentiation requires dynamic 3-dimensional change. It is this very functionality which we investigate. Right @s_cuarter? @epigen_papers
13. We have shown the effect in functional primary cells of locus specific loop-alterations to decreased accessibility, decreased expression & finally to an observed defect in hematopoiesis which we can rescue through restoration of a downstream target gene #FunctionalEpigenetics
14. We thank everyone involved in this great team effort! @bowman_rl @dekker_lab And hope that both our Stag2 results and reagents are valuable to other labs and that @epigenetichulk won't smash!
15. Thanks to @ASH_hematology @DamonRunyon @NCIDirector @EvanMDS @LLSResearch for funding my early career development and this exciting project!
16. And most importantly thank you to @rosslevinemd the most inspiring and supportive mentor. @NYC_Postdoc and @PhDStudents all should look at @RossLevineLab for a career in impactful translational science to #jointhebattle against cancer!
17. Don't miss @rosslevinemd, @sloan_kettering present this work tomorrow at 5:00 in Van Horne A/B in his talk, "Role of Mutations in Epigenetic Regulators in Pathogenesis of AML"#KS3Dgenome #KSepigen
