Fig. 6: Red-cell size regulated by Epo concentration in mice and humans.

a, b Epo regulates erythroblast diameter. CFU-e progenitors (‘S0’) enriched from wild-type fetal livers were differentiated in vitro in a range of Epo concentrations and analyzed at 48 h. Representative of two independent experiments. a S0 cells differentiate into the S1, S2, and S3 subsets by 48 h. b Cell diameter distributions for each erythroblast subset and Epo concentration. Violin lines are 25th, 50th, and 75th percentile. White circles mark the mean. c Nuclear offset measures nuclear eccentricity, independently of cell size. It is the ratio of the delta centroid (distance between the centers of the cell and the nucleus, Δ) and cell diameter. Nuclear offset increases during erythroid morphological maturation. d–g Mice were injected with saline (n = 2) or Epo (n = 2 mice with either 5 U, 20 U, or 100 U). Bone marrow analyzed at 48 h. d Nuclear offset quintiles for Ter119⁺ erythroblasts in saline-injected mice. e CD71/forward-scatter (FSC) histograms for the nuclear offset quintiles in (d) of Ter119⁺ erythroblasts. Quintile values that were determined for saline-injected mice were also applied to the Epo-injected mice. Sequential quintiles are seen to contain increasingly mature erythroblasts. f Cell diameter in each nuclear offset quintile in (e), for each Epo dose. Violin lines are 25th, 50th, and 75th percentile, white circle marks the mean. Data representative of n = 2 mice per Epo dose. g Median cell diameter and median nuclear offset values in each nuclear offset quintile, for mice injected with Epo (100 U) or Saline. Datapoints are individual mice. h Human intervention studies. Epo was administered during the period indicated. In study #1, n = 25 subjects were treated with Epo and n = 9 subjects with placebo. In study #2, n = 24 each for placebo and Epo. Data is fractional change relative to the baseline values of each participant. Additional hematological parameters and data for placebo groups are in Supplementary Figs. 14, 15 and Supplementary statistical analysis. MCV, mean corpuscular volume; Retics, reticulocyte count. i RDW_SD and reticulocyte counts for human intervention study #1 described in panel (h).