# Crip2 preserves hematopoietic stem and progenitor cell production through inhibition of Notch signals

## TL;DR

Crip2 helps produce blood stem cells by blocking Notch signals, which could improve treatments for blood disorders.

## Contribution

Crip2 is newly identified as a regulator of Notch repression in hematopoietic stem cell development.

## Key findings

- Crip2 is essential for proper endothelial cell environment to generate hematopoietic stem and progenitor cells.
- Loss of Crip2 and Crip3 leads to impaired HSPC emergence and upregulated Notch signaling.
- Inhibiting Notch rescues HSPC production in embryos lacking Crip2 and Crip3.

## Abstract

Hematopoietic stem and progenitor cells (HSPCs) have multilineage potential and sustain long-term self-renewal. Deriving patient-specific HSPCs has immense therapeutic potential to overcome the shortage of compatible donors for transplantation. In zebrafish, hemogenic endothelium (HE) is a specialized collection of dorsal aortic endothelial cells (ECs) that give rise to HSPCs. Our data reveal that Cysteine rich intestinal protein 2 (Crip2) has a previously unrecognized function in establishing the proper EC environment for HSPC specification. To investigate the requirement of Crip2, we generated loss-of-function alleles in crip2 and crip3, a gene family member with cardiovascular expression. crip2−/−;crip3−/− (cripDM) embryos exhibit decreased HSPC emergence with impaired lineage derivative production. Single cell RNA-sequencing of kdrl:mCherry+ ECs reveals upregulation of vascular development signature and failure to repress Notch signals during the vital transition of HE specification to HSPC emergence. Moreover, our data underscore that inhibition of Notch promotes HSPC generation in cripDM embryos and Crip genes operate through NF-κB to limit Notch. Identification of Crip2 as a novel regulator of Notch repression in HE will enhance our understanding of cues necessary to improve human HSPC production in vitro.

Summary: The expression of Crip2 is finely tuned to repress Notch signals at the emergence of HSPCs, a discovery that could support the discovery of tools to repopulate fully functional definitive blood precursors in diseased states.