BCL11A (BCL11 transcription factor A; HGNC:13221, NCBI Gene ID 53335) is a human locus mapped to chromosome band 2p16.1 that encodes C2H2 zinc-finger transcriptional repressor BCL11A-XL (835 aa). BCL11A acts in direct binding to -115 bp TGACCA motif of HBG1 & HBG2 promoters + NuRD complex recruitment to silence fetal hemoglobin (HbF) after birth, together with HBG1 (A-Gamma Fetal Globin Promoter Bound by BCL11A at -115 bp), HBG2 (G-Gamma Fetal Globin Promoter Bound by BCL11A at -115 bp), and HBB (Adult Beta-Globin Gene Mutated in SCD & Beta-Thalassemia). Encodes the C2H2 zinc-finger transcription factor BCL11A that silences fetal gamma-globin (HBG1/HBG2) after birth; its erythroid enhancer is the target of the first approved CRISPR therapy Casgevy.
Direct binding to -115 bp TGACCA motif of HBG1 & HBG2 promoters + NuRD complex recruitment to silence fetal hemoglobin (HbF) after birth
Clinical / Therapeutic Role
Erythroid +58 kb enhancer is the exact target of the first FDA-approved CRISPR-Cas9 medicine exagamglogene autotemcel (Casgevy) for Sickle Cell Disease & Beta-Thalassemia; germline LoF causes Dias-Logan syndrome
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 5-exon gene on chromosome 2p16.1 generating four alternatively spliced isoforms (with the 835-amino-acid Extra-Long isoform BCL11A-XL containing six C2H2 Kruppel-like zinc fingers—ZnF4, ZnF5, and ZnF6 at the C-terminus mediating sequence-specific DNA binding—required for globin silencing); crucially, intron 2 harbors three erythroid-specific DNase-I hypersensitive enhancer elements (+55, +58, and +62 kb from the transcription start site) that drive BCL11A expression strictly in red blood cell precursors.
Cellular & Tissue Expression Profile: Expressed in adult-stage bone marrow erythroid progenitors (absent in fetal liver erythroblasts), B lymphocytes, plasmacytoid dendritic cells, and developing cerebral cortical projection neurons (as a subunit of mammalian SWI/SNF BAF chromatin-remodeling complexes).
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Orchestrates the human fetal-to-adult hemoglobin switch around birth: in adult bone marrow erythroblasts, KLF1 and GATA1-TAL1 activate the intron 2 erythroid enhancers of BCL11A; the resulting BCL11A-XL protein uses its C-terminal ZnF4–6 cluster to bind directly to the 5-prime-TGACCA-3-prime motif at position -115 bp in the proximal promoters of both fetal gamma-globin genes (HBG1 and HBG2), recruiting the NuRD (CHD4-HDAC1/HDAC2) corepressor complex to silence HbF and redirect the upstream Locus Control Region (LCR) to transcribe adult beta-globin (HBB).
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Discovered through human genome-wide association studies of HbF levels (Menzel, Uda, Sankaran, Orkin, 2007–2008): common non-coding variants inside the intron 2 erythroid enhancer of BCL11A reduce erythroid BCL11A expression, elevate adult HbF, and dramatically ameliorate the clinical severity of sickle cell disease and beta-thalassemia; conversely, heterozygous germline coding mutations in BCL11A itself cause Dias-Logan syndrome (intellectual developmental disorder with persistence of fetal hemoglobin), proving that whole-gene BCL11A loss impairs brain and B-cell development whereas disrupting only the erythroid enhancer is safe.
Therapeutic & Clinical Pharmacology: This tissue-specific enhancer architecture enabled the historic clinical triumph of exagamglogene autotemcel (Casgevy / exa-cel, in December 2023 the first FDA-approved therapy to use CRISPR-Cas9): autologous CD34+ hematopoietic stem and progenitor cells are electroporated ex vivo with SpCas9 and a single guide RNA (SPY101) targeting the GATA1-binding motif inside the +58 kb erythroid enhancer of BCL11A—reducing erythroid BCL11A without affecting brain or B-cell BCL11A, restoring pan-cellular fetal hemoglobin (HbF >40%), and eliminating vaso-occlusive crises in sickle cell disease and transfusion dependence in beta-thalassemia.