The Transcription Factor ZBP-89 Controls Generation of the Hematopoietic Lineage in Zebrafish and Mouse Embryonic Stem Cells.

Hematopoietic development is closely linked to that of blood vessels and the two processes are regulated in large part by transcription factors that control cell fate decisions and cellular differentiation. Both blood and blood vessels derive from a common progenitor, termed the hemangioblast, but the factors specifying development and differentiation of this stem cell population into the hematopoietic and vascular lineages remain ill defined. Here we report that knockdown of the Krüppel-like zinc finger ZBP-89 (ZNF148) in zebrafish embryos results in a bloodless phenotype, caused by disruption of both primitive and definitive hematopoiesis, leaving primary blood vessel formation intact. Expression of the primitive (Scl, Lmo2, Gata2, Gata1) and definitive (Runx1, c-Myb) hematopoietic stem cell lineage markers in ZBP-89 morphants were significantly decreased while expression of the lymphopoiesis lineage markers Ikaros and Gata3 was unaffected. These developmental HSC defects are rescued by injection of human ZBP-89 RNA, SCL RNA or ZBP-89 cDNA under control of the zebrafish Flk1 promoter. Injection of ZBP-89 RNA into cloche zebrafish embryos, which lack the hematopoietic and endothelial lineages, rescued hematopoiesis but not vasculogenesis. Overexpression of ZBP-89 in wild type zebrafish expanded hematopoietic progenitors (Scl⁺, Lmo2⁺, Gata1⁺) but reduced the endothelial cell markers FLK1 and TIE1. Forced expression of ZBP-89 in mouse embryonic stem cell cultures also induced the expansion of hematopoietic progenitors (c-KIT⁺, SCA1⁺) and definitive hematopoietic cell population (CD45⁺), but inhibited sprouting angiogenesis and the CD31⁺, VE-Cadherin⁺ endothelial cell population. These findings establish a unique regulatory role for ZBP-89, positioned at the interface between early blood and blood vessel development.