CCBE1 is not required for postnatal erythropoiesis or bone marrow EBI formation. (A) Loss of Ccbe1 was induced by tamoxifen administration to Ub-CreERT2; Ccbe1^fl/lacZ (postnatal KO) and Ub-CreERT2; Ccbe1^fl/+ (control) mice and hematocrits measured 12 weeks later. (B) Ub-CreERT2; Ccbe1^fl/lacZ (postnatal KO) and control Ub-CreERT2; Ccbe1^fl/+ (control) mice were phlebotomized 12 weeks after tamoxifen-induced deletion of Ccbe1 and hematocrits measured at the indicated time points after phlebotomy. n = 5 in each group. (C,D) Native EBIs isolated from postnatal KO (KO) bone marrow have similar numbers of Ter119⁺ erythroblasts adherent to F4/80⁺ macrophages as those from wild-type littermates. (E,F) Reconstituted EBIs reveal normal adhesion of CCBE1-deficient (KO) erythroblasts to wild-type F4/80⁺ macrophages, and vice versa. n = 12 to 45 islands per group; error bars indicate SEM. EB, erythroblast; MΦ, macrophage; WT, wild-type.