Cebpa is required for haematopoietic stem and progenitor cell generation and maintenance in zebrafish.

The CCAAT enhancer binding protein alpha (CEBPA) is crucial for myeloid differentiation and the balance of haematopoietic stem and progenitor cell (HSPC) quiescence and self-renewal, and its dysfunction can drive leukemogenesis. However, its role in HSPC generation has not been fully elucidated. Here, we utilized various zebrafish mutants to investigate the function of Cebpa in the HSPC compartment. Co-localization analysis showed that expression is enriched in nascent HSPCs. Complete loss of Cebpa function resulted in a significant reduction in early HSPC generation and the overall HSPC pool during embryonic haematopoiesis. Interestingly, while myeloid differentiation was impaired in N-terminal mutants expressing the truncated zP30 protein, the number of HSPCs was not affected, indicating a redundant role of Cebpa P42 and P30 isoforms in HSPC development. Additionally, epistasis experiments confirmed that Cebpa functions downstream of Runx1 to regulate HSPC emergence. Our findings uncover a novel role of Cebpa isoforms in HSPC generation and maintenance, and provide new insights into HSPC development.