Cis-regulation between Irf8 enhancers during cDC1 development (ATAC-Seq)

Type 1 classical dendritic cells (cDC1s) development requires the transcription factor IRF8, and IRF8 mutations cause severe combined immunodeficiency, including disseminated bacille Calmette-Guérin (BCG) disease. IRF8 regulated enhancers are required for Irf8 expression in early DC progenitors and mature cDC1s. The E-protein-dependent +41 kb enhancer gains accessibility and activates transcription in common DC progenitors (CDPs), and its depletion abrogated pre-cDC1s specification. The Batf3-dependent +32 kb enhancer gains accessibility and activates transcription in pre-cDC1 progenitors, and its depletion impaired cDC1 maturation. The +32 kb Irf8 enhancer locus bears an enhancer transcript, and the production of enhancer RNA (eRNA) Gm39266 is dependent on +41 kb Irf8 enhancer. It was unclear whether the +32 kb and +41 kb enhancers act independently or cooperate to regulate Irf8 expression. We dissected the mechanisms using +32/+41 compound heterozygous mice, and found that while the +41 kb enhancer suffices for pre-cDC1 progenitor specification, the +32 kb and +41 kb enhancers must reside on one allele to support cDC1 maturation. The +41 kb enhancer cis-regulates chromatin accessibility and BATF3 binding at +32 kb enhancer, independent of eRNA Gm39266 transcripts or transcription across +32 kb Irf8 enhancer. Overall design: Examination of chromatin accessibility in the pre-cDC1 progenitors from Irf8 +32+/- and +32/+41 compound heterozygous mice by ATAC-seq.