HEMATOPOIESIS The homeoprotein Hex is required for hemangioblast differentiation

The first hematopoietic and endothelial progenitors are derived from a common embryonic precursor termed the heman-gioblast. The genetic cascades that regu-late the differentiation of the hemangio-blast to hematopoietic and endothelial cells are largely unknown. In general, much of embryonic development is coor-dinately regulated by temporal and spa-tial expression of transcription factors, such as the Homeobox (Hox) gene family. We and others isolated a divergent ho-meobox gene termed Hex (or Prh) that is preferentially expressed in hematopoietic and endothelial cells. Using in vitro Hex/ embryonic stem (ES) cell differentiation, in vivo yolk sac hematopoietic progenitor assays, and chimeric mouse analysis, we found that Hex is required for differentia-tion of the hemangioblast to definitive embryonic hematopoietic progenitors and to a lesser extent endothelial cells. Therefore, Hex is a novel regulator of hemangioblast differentiation to hemato-poietic and endothelial cells. (Blood. 2003