# In vivo CRISPR screening identifies SAGA complex members as key regulators of hematopoiesis

## TL;DR

A CRISPR screen in blood stem cells finds that the SAGA complex is crucial for normal blood production and its loss disrupts cell maturation and causes disease-like changes.

## Contribution

Identifies SAGA complex members as novel regulators of hematopoiesis through in vivo CRISPR screening.

## Key findings

- Loss of Tada2b or Taf5l strongly inhibits hematopoiesis and causes immature cell buildup in bone marrow.
- SAGA complex disruption reduces H3K9ac and alters H2Bub, leading to interferon pathway activation and reduced mitochondrial activity.
- Loss of SAGA complex components enhances growth of human myelodysplastic syndrome cells in vivo.

## Abstract

The biological mechanisms that sustain the vast blood production required for healthy life remain incompletely understood. To search for cell intrinsic regulators of hematopoiesis, we perform a genome-wide in vivo hematopoietic stem and progenitor cell (HSPC)-based CRISPR knockout screen. We discover SAGA complex members, including Tada2b and Taf5l, as key regulators of hematopoiesis. Loss of Tada2b or Taf5l strongly inhibits hematopoiesis in vivo, causing a buildup of immature hematopoietic cells in the bone marrow. The SAGA complex deposits histone H3 lysine 9 acetylation (H3K9ac) and removes histone H2B ubiquitination (H2Bub). Loss of Tada2b leads to a reduction in H3K9ac levels and altered H2Bub enrichment in HSPCs, implicating disruption of SAGA complex activity. This is associated with upregulation of interferon pathway genes, reduced mitochondrial activity, and increased megakaryocyte progenitor cell commitment. Loss of these factors also enhances the cell outgrowth and the interferon pathway in an in vivo human myelodysplastic syndrome cell line model. In summary, this study identifies the SAGA complex as an important regulator of hematopoiesis.

A CRISPR screen reveals that loss of structural components of the SAGA complex derails hematopoiesis by decoupling epigenetic control. This halts stem cell maturation, triggers a pathogenic interferon program and boosts human MDS-L cell growth.