Abstract
The signal transducer Stat5 plays a key role in the regulation of hematopoietic differentiation and hematopoietic stem cell function. To evaluate the effects of Stat5 signaling in the earliest hematopoietic progenitors, we have generated an embryonic stem cell line in which Stat5 signaling can be induced with doxycycline. Ectopic Stat5 activation at the point of origin of the hematopoietic lineage (from day 4 to day 6 of embryoid body differentiation) significantly enhances the number of hematopoietic progenitors with colony-forming potential. It does so without significantly altering total numbers or apoptosis of hematopoietic cells, suggesting a cell-intrinsic effect of Stat5 on either the developmental potential or clonogenicity of this population. From day-6 embryoid bodies, under the influence of Stat5 signaling, a population of semiadherent cells can be expanded on OP9 stromal cells that is comprised of primitive hematopoietic blast cells with ongoing, mainly myeloid, differentiation. When these cells are injected into lethally irradiated mice, they engraft transiently in a doxycycline-dependent manner. These results demonstrate that the hematopoietic commitment of embryonic stem cells may be augmented by a Stat5-mediated signal, and highlight the utility of manipulating individual components of signaling pathways for engineering tissue-specific differentiation of stem cells.