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We are grateful for our erythroid and myeloid malignancy colleagues for their constructive feedback, and many thanks to @bloodjournals.hematology.org for helping us make our paper stronger.

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This work would not have been possible without the support of our funding sources @alt-thenci.bsky.social #EvansMDS @ash.hematology.org @damonrunyon.org and @the-asci.org.

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This work was led by the incomparable @ColumbiaPS MD/MS student Varun Sudunagunta (incoming PGY-1 at MGH) and @cohesinlab.bsky.social @columbiacancer.bsky.social in collaboration with Mohan Narla and Hongxia @newyorkbloodcenter.bsky.social

In summary, our work identifies chromatin accessibility as a molecular gatekeeper of TF binding specificity and lineage fate decisions. Our data provides a mechanistic basis for ESA resistance in STAG2-mutant MDS and a framework for future chromatin-targeted interventions.

Bottom Line: Chromatin accessibility doesn’t just permit transcription – it determines where transcription factors bind and act.

We extended findings to human CD34⁺ cells & MDS patients, recapitulating that STAG2 loss impaired erythroid differentiation and resulted in accessibility-driven retargeting of GATA1 to megakaryocyte loci.

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Loss of STAG2 skews differentiation toward megakaryocytes—partially corrected by Fli1 knockdown, highlighting that erythroid differentiation is more complex than the expression of a single TF.

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STAG2 does not directly interact with GATA1, but co-localizes with ~60% of GATA1 sites, with strong enrichment at erythroid loci – consistent with a role in focusing GATA1 output.

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Importantly, GATA1 expression is unchanged. This is not a transcription factor problem – it’s a targeting problem. Chromatin accessibility dictates where GATA1 engages, and therefore which lineage program is executed.

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Multi-omic profiling revealed a striking polarity: - ↓ accessibility, GATA1 binding, and expression at erythroid genes - ↑ accessibility, GATA1 binding, and expression at megakaryocyte genes Same TF, but different output 🤯

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Loss of Stag2 led to: - ↓ erythroid progenitors - ↑ megakaryocyte progenitors and megakaryocytes - Impaired terminal erythroid maturation

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We hypothesized that STAG2 enforces lineage specificity by regulating chromatin accessibility at GATA1 target sites.

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Because TFs depend on chromatin context, we asked whether DNA accessibility enforces lineage specificity.

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GATA1 controls both erythroid and megakaryocyte fates—but how lineage-specific output is enforced remains unclear. This raises a key question: If GATA1 is broadly expressed, what determines whether it drives erythroid versus megakaryocyte programs?

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Stag2 dependent chromatin remodeling enforces the erythroid-specific Gata1 cistrome

Transcription factors don’t fail in MDS—they’re misdirected. Today in Blood, we show how loss of STAG2 rewires chromatin accessibility to redirect GATA1 and alter blood cell fate. ashpublications.org/blood/articl...

ashpublications.org

Key Points. Stag2 reprograms Gata1 cistrome specificity via chromatin accessibility, a key determinant of transcription factor lineage discrimination.Loss

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TL;DR Stag2 enforces erythroid fate by shaping chromatin to guide GATA1 binding, showing how TFs + chromatin = cell fate We had so much fun working with Hongxia &🩸giant Mohan Narla. We appreciate funding support from NCI, @ash.hematology.org, @the-asci.bsky.social, #EvansMDS @damonrunyon.org

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Summary We identify Stag2 as a key enforcer of erythroid identity through its role in shaping the chromatin landscape that guides Gata1 binding. This underscores the importance of coordinated transcription factor and chromatin interactions in lineage specification.

Human Relevance We extended findings to human CD34⁺ cells & MDS patients: - STAG2 loss impaired erythroid differentiation - Altered GATA1 target gene expression 🧍‍♂️➡️🧬⬅️🐭

Functional Validation Functionally, we observed that Stag2 KO EryPs: - Produced fewer erythroid cells - Generated more megakaryocytes

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Multi-omic Insight RNA-seq, ATAC-seq, and GATA1 CUT&RUN of EryPs revealed: - ↓ accessibility & GATA1 binding at erythroid genes - ↑ accessibility & GATA1 binding at megakaryocyte genes Stag2 loss rewires the GATA1 cistrome.

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Phenotypic Findings Loss of Stag2 led to: - ↓ erythroid progenitors - ↑ megakaryocyte progenitors and megakaryocytes Impaired terminal erythroid maturation Basically, the hematopoietic GPS got rerouted. 🧭➡️🧬

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a man in a pirate costume is holding a camera and pointing

Hypothesis and Model We hypothesized that Stag2, a cohesin complex member recurrently mutated in MDS, modulates chromatin accessibility to guide GATA1’s lineage-specific binding. To test this, we profiled erythropoiesis in Stag2 KO mice.

media.tenor.com

ALT: a man in a pirate costume is holding a camera and pointing

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GATA1 is a master regulator of 🩸, yet it has pleiotropic functions, particularly in erythroid/megakaryocytic ontogeny. Inspired by the open Qs in John Crispino's review (PMID: 15659348) we wanted to understand how GATA1 enforces lineage specificity across divergent fates.

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