HIC2 links LIN28B/let-7 to HBG transcription. (A) The balance depicts abundance of RNA binding protein LIN28B in fetal cells resulting in blocked let-7 miRNA biogenesis. HIC2 can then inactivate the BCL11A enhancer, allowing transcription of HBG and HbF production. (B) In adult cells, LIN28B is low and let-7 is abundant, binding to the 3′ UTR of HIC2 and leading to its degradation. Now, GATA1 can occupy the BCL11A enhancer, BCL11A is activated and then the protein silences HBG. Professional illustration by Somersault18:24.