Model of developmental regulation of HIC2 by let-7 miRNAs. During fetal erythropoiesis, LIN28B is highly expressed and blocks let-7 biogenesis. Without the inhibition by let-7, HIC2 represses BCL11A transcription. During adult erythropoiesis, LIN28B is downregulated, derepressing let-7 biogenesis, and inhibiting HIC2. BCL11A is highly transcribed and silences HBG.