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A novel system to study early hematopoietic development is described. This report documents the in vitro capacity of murine embryonic stem (ES) cells to differentiate into hematopoietic precursors of most, if not all, of the colony-forming cells found in normal bone marrow. This system is used to correlate the genetic expression of cytokines, their receptors, the beta-globins, and the hematopoietic cell surface markers throughout the time course of ES cell differentiation with the hematopoietic development that occurs in these cultures. Our results indicate that there is a strong transcriptional activation, in a well-defined temporal order, of most of these genes including erythropoietin (Epo), CSF-1, IL-4, beta-globins, as well as the receptors for Epo, CSF-1, and IL-4. IL-3 and GM-CSF were not expressed during the first 24 days of ES cell differentiation. In contrast, the Steel (Sl) factor (SLF) was expressed early and underwent substantial up-regulation during this differentiation, and its receptor, c-kit, was expressed relatively constantly throughout the culture period. Our results are consistent with the conclusion that SLF, Epo, IL-4, and IL-6 are important during the early stages of ES cell differentiation and hematopoietic development. Furthermore, these results argue strongly that IL-3 and GM-CSF are not critical to early hematopoiesis. This system offers a unique in vitro model for studying hematopoietic development at the earliest possible stages.
Schmitt et al. (Wed,) studied this question.