Importance of Ldb1 to embryonic and adult β-globin gene expression during erythroid differentiation. Wild-type (WT) or Ldb1-null mutant (Ldb1^−/−) ES cells were differentiated along erythroid lines into EBs with erythropoietin for 8 days as described under “EB differentiation.” (A) Morphology of WT or Ldb1^−/− EB after 8 days of differentiation. (B-C) Total RNA was isolated at the indicated day of differentiation to determine expression of (B) Ldb1, or (C) ϵγ, βH1, and βmaj-globin. Each value was normalized with 18S ribosomal RNA. Error bars represent the SEM from independent RNA preparations.