Growth factor and cytokine pathways in primitive erythroid progenitors. (A) Changes in expression of genes encoding growth factor or cytokine receptors and downstream signaling components in E7.5 and E8.5 EryPs. Shown in this table are median expression levels (log2) from the microarray and linear fold change in expression. (B) Effect of TGF-β1 on formation of EryP progenitors. EryPs were FACS sorted from whole E8.5 embryos and plated in the methylcellulose colony assays in the presence of the indicated concentrations of TGF-β1. Data represent the average of triplicate samples from 4 experiments; error bars represent SEM. (C) Expression of c-kit and Tie-2 protein on EryP at E7.5, E8.5, and E9.5. (D) c-kit marks EryP progenitors within the GFP(+) cell population from E8.5 embryos. Cells were FACS sorted and plated in triplicate in methylcellulose progenitor assays. Colonies were scored at day 5. One representative experiment of 3 is shown; error bars represent SEM (E) Tie-2 marks EryP progenitors within the GFP(+) cell population from E8.5 embryos. Cells were FACS sorted and plated in triplicate in methylcellulose progenitor assays. Colonies were scored at day 5. One representative experiment of 3 is shown; error bars represent SEM (F) Real-time RT-PCR analysis of mRNA expression of Tgf-β1, Ang-1, Scf, and Epo in FACS-sorted EryPs, visceral endoderm, and endothelial cells from YS or in cells from whole embryos at E8.5. Expression levels are shown relative to Ubb.
