Stat5 Signaling Specifies Basal versus Stress Erythropoietic Responses through Distinct Binary and Graded Dynamic Modalities
Figure 6
Stat5 functions in EpoR-HM and Stat5−/− fetal liver.
(A, B) Increased erythroblast apoptosis in Stat5−/− but not in EpoR-HM fetal liver. Freshly harvested fetal livers from E13.5 Stat5−/− or EpoR-HM embryos and from littermate or strain-matched controls were incubated in the absence of Epo for 90 min. Cells were then labeled with 7-AAD to exclude dead cells, and with Annexin V, CD71, and Ter119 to assess apoptosis. Representative histograms are shown for S1 cells in Stat5−/− fetal liver and in matched control (A), and for S1 cells of EpoR-HM fetal liver and matched control (B). Summary of Annexin-V+ cells in three independent experiments is shown in corresponding lower panels; each data point corresponds to an individual embryo, the black line is the mean for all embryos of a given genotype. Number of embryos analyzed: EpoR-HM = 15, strain and age matched controls = 20; Stat5−/− = 5, littermate controls = 5. No statistically significant difference was detected between EpoR-HM and control embryos; the difference between Stat5−/− and control embryos is significant (p = 0.0007, two-tailed t test, unequal variance). (C, D) Cell-surface CD71 in Stat5−/− and EpoR-HM fetal liver. E13.5 or E14.5 fetal liver from Stat5−/−, EpoR-HM, or matched control embryos were labeled with CD71 and Ter119. Non-viable cells were excluded with 7-AAD. Top panels show representative flow-cytometric CD71/Ter119 profiles of viable, non-fixed fetal liver cells. Lower panels show data for all Stat5−/− embryos (n = 7, each data point is an individual embryo), Stat5+/− (n = 11), and wild-type littermates (n = 8), and for EpoR-HM (n = 19) and strain-matched controls (n = 14). Difference between HM and matched control is significant (p<0.002, unpaired t test); Differences between Stat5+/−, Stat5−/−, and wild-type mice are all significant (p<0.0001, one-way ANOVA).