Dynamic changes in erythropoietic activity in the C57BL/6 mouse liver after birth. (A) Terminal erythroid differentiation in the liver for the first 12 days after birth (P1 to P12) was measured by flow cytometry using CD44 vs FSC as markers. (B) The total number of erythroblasts in the liver from P1 to P15 was determined by flow cytometry using Ter119⁺ CD44^hi populations of erythroid cells (red gate is shown in panel A). (C) Absolute number of liver cells from P1 to P15. (D) Evolution of the mouse body weight (blue solid lines) vs liver weight (red solid line) from P1 to P15. (E) Erythropoietic activity in the liver was determined by immunohistochemistry using Ter119 staining at the indicated days (left panels, original magnification ×20; right panels, original magnification ×40). n = 4-13 animals per day; data are presented as mean ± SEM. *P < .05, **P < .01, ***P < .001, ***P < .0001, indicated postnatal day vs P1 (ANOVA with Tukey’s post hoc test with corrections for multiple comparisons).