# Nap1L4a Cooperates with Scl/Klf1 to Recruit H2A.Z in Mediating Interactions Among Cis‐Regulatory Elements and Transcription Required for Primitive Erythropoiesis in Zebrafish

## TL;DR

Nap1l4a helps regulate early red blood cell formation in zebrafish by working with key proteins to modify chromatin structure and gene activity.

## Contribution

Nap1l4a's role in recruiting H2A.Z and cooperating with Scl/Klf1 to regulate erythropoiesis is newly identified.

## Key findings

- Nap1l4a interacts with Scl and Klf1 to recruit H2A.Z and remodel cis-regulatory elements.
- Nap1l4a deficiency disrupts chromatin accessibility and alters histone marks in erythroid cells.
- Nap1l4a modulates the WNT/β-Catenin pathway to regulate primitive erythropoiesis.

## Abstract

The chromatin remodeler nucleosome assembly protein 1‐like 4 (Nap1L4) is highly expressed in megakaryocyte‐erythroid progenitors (MEPs) and erythroid cells. Mutations, deletions, and aberrant expressions of Nap1L4 are observed in diseases such as acute myeloid leukemia (AML). However, the roles of Nap1l4a in erythropoiesis and related diseases, as well as the underlying mechanisms, remain unknown. Here, it is demonstrated that zebrafish nap1l4a homozygous mutants (nap1l4a
−/−) are more sensitive to hypoxia stress during the early embryonic stage and exhibit impaired primitive erythropoiesis. Mechanistically, zebrafish Nap1l4a interacts with the erythropoietic transcription factors (TFs) Scl and Klf1, and recruits the histone variant H2A.Z. This interaction remodels the cis‐regulatory element (CRE) landscape and promotes nascent RNA transcription of erythropoietic genes. Meanwhile, Nap1l4a deficiency impairs chromatin accessibility at the epigenetic regulators kdm6b and kmt2c. This results in expanded H3K27me3 and diminished H3K4me1 in erythrocytes, leading to altered histone landscapes at erythropoiesis TF loci and reduced TF expression. Moreover, Nap1l4a regulates primitive erythropoiesis by transcriptionally and epigenetically modulating the canonical WNT/β‐Catenin pathway. Together, the findings reveal a lineage‐selective transcription, with histone epigenomics‐dependent role for nap1l4a in vertebrate primitive erythropoiesis. These findings highlight potential mechanisms underlying human blood disorders and hypoxia responses associated with Nap1l4a deficiency.

Nap1l4a is required in erythropoiesis and hypoxia responses via physical interaction with Klf1 and Scl to recruit the histone variant H2A.Z. This facilitates its associated cis‐regulatory element (CRE) remodeling and the consequent chromatin assembly, and activates the transcription of erythroid lineage‐specific genes.