Hypoxia regulates EryP-progenitor activity. (A) Expression of genes involved in glucose metabolism during EryP maturation. Relative mRNA levels from the microarrays expressed on a log₂ scale. Note the isoform switching from Pgk1 to Pklr. (B) Transcripts known to be induced by hypoxia are down-regulated during EryP maturation. Absolute expression (log₂ scale) and fold change in expression are shown for the period from E8.5-E11.5. Expression cutoff, 6.0. (C) Hypoxia increases EryP-progenitor numbers in culture. E8.5 EryPs were FACS sorted, plated in methylcellulose, and incubated under atmospheric or low-oxygen (5%) conditions. Total EryP colony numbers were scored at day 5. (D) Increase in EryP colony size under low-oxygen conditions. Photographs of representative EryP colonies grown at atmospheric or low oxygen conditions are shown. Scale bar, 50 μm. The graph displays the mean radius of EryP colonies (day 4) grown at atmospheric or low oxygen. The EryP colonies that formed in low oxygen were significantly larger than those formed at atmospheric oxygen (33 vs 23.3 μm mean colony radius, respectively). (E) Giemsa staining of cytocentrifuged cells from EryP colonies grown at atmospheric or low oxygen and harvested at day 4. Scale bar, 50 μm. (F) Expression of hypoxia-regulated genes in EryP colonies grown at atmospheric or low oxygen. Colonies were harvested at day 4 and RNA was prepared for qRT-PCR analysis. Expression levels are shown relative to Ubb. Cells grown under hypoxic conditions maintain higher-level expression of these genes than cells grown at atmospheric oxygen. These genes are normally down-regulated as EryP progenitors mature (panel A).