3073 – THE ROLE OF RETINOIC ACID SIGNALING IN HUMAN DEFINITIVE HEMATOPOIETIC MESODERM DEVELOPMENT

• Published in: Experimental hematology Vol. 137; p. 104395
• Main Authors: Fernandez, Nestor, Durland, Lauren, Atkins, Michael, Garcia, Analucia, Keller, Gordon, Kennedy, Marion, Sturgeon, Christopher
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.08.2024
• ISSN: 0301-472X
• DOI: 10.1016/j.exphem.2024.104395

Embryonic hematopoiesis develops in a layered fashion to generate distinct hematopoietic programs that are unique in both their spatiotemporal and developmental characteristics. Definitive hematopoiesis is especially unique in that it generates hematopoietic stem cells (HSCs), the self-renewing stem cells at the apex of the hematopoietic hierarchy. A recent directed differentiation study using human pluripotent stem cells (hPSCs) has shown that retinoic acid (RA) is required for specifying definitive hematopoiesis derived from KDR+CD184+ mesoderm. To further interrogate the mesodermal origins of this RA-dependent definitive hematopoietic mesoderm, we employed a transgenic reporter line that contains tdTomato (tdT) in the locus of ALDH1A2, a gene encoding an enzyme that synthesizes retinoic acid from retinaldehyde. With this line we show that ALDH1A2-tdT expression is exclusive to definitive hematopoietic mesoderm and not its primitive yolk-sac counterpart. Additionally, the source of the multilineage (erythroid, myeloid, lymphoid) RA-dependent definitive hematopoiesis was found to be the KDR+CD184+ALDH1A2-tdT- mesoderm, suggesting a non-cell autonomous mechanism. ALDH1A2 null hPSCs failed to generate RA-dependent definitive hematopoiesis with retinol supplementation, underscoring that ALDH1A2 is essential for this process. The T lymphoid cells derived from the RA-dependent program were also found to contain Vδ1+ γ/δ T cells, a subset of γ/δ T cells characteristic of late fetal gestation following the initiation of definitive hematopoiesis. Collectively, this work elucidates the origins of the definitive hematopoietic program in relation to mesodermal RA signaling.