Mouse embryonic stem (ES) cells that differentiate in serum-supplemented media give rise to hematopoietic cells such as erythrocytes and macrophages. Along the way, they pass through three intermediate stages, epiblast-like, mesodermal, and hemangioblast, which are distinguishable by gene expression profile, developmental potential, and morphology. Pearson et al. describe a serum-free culture method that recapitulates this differentiation pathway, and they used it to identify the stage-specific requirements for each cytokine. Cell identities were determined by quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis of marker gene expression and by developmental potential as assayed by cell morphology in colonies after replating. A cocktail of bone morphogenetic protein 4 (BMP4), fibroblast growth factor 2 (FGF2), activin A, and vascular endothelial growth factor (VEGF) mimicked serum in directing ES cell fate. ES cells treated with BMP4 passed through an epiblast-like stage before expressing mesoderm-specific genes such as Mesp2 and Tbx6. Without further treatment, mesodermal precursor cells gave rise to hemangioblasts and other mesodermal derivatives that were not observed in serum-directed differentiation, indicating that they retained pluripotency. However, continuing the treatment of these cells with a combination of FGF2 and activin A induced only the formation of hemangioblasts. Addition of VEGF caused the cells to differentiate into hematopoietic cells. The authors have identified a handful of factors that can direct the differentiation of ES cells to a particular subset of fates in vitro, a necessary prelude to understanding how lineage restriction may by regulated in stem cells in vivo and how it may be manipulated in vitro.
S. Pearson, P. Sroczynska, G. Lacaud, V. Kouskoff, The stepwise specification of embryonic stem cells to hematopoietic fate is driven by sequential exposure to Bmp4, activin A, bFGF and VEGF. Development 135, 1525-1535 (2008). [Abstract] [Full Text]