Dendritic cells (DCs) orchestrate immune responses. Their development is controlled by transcription factors, but epigenetic mechanisms remain poorly understood. DOT1L emerges as a key epigenetic regulator in immune cells. Mapping DOT1L-mediated histone H3K79 methylation in canonical DC subsets revealed that DOT1L modified common and DC subset-specific genes. Deletion of Dot1l in vivo or in vitro decreased myeloid progenitors and increased cDC2s, whereas cDC1s remained unchanged. In addition, in vitro deletion of Dot1l led to loss of plasmacytoid DCs (pDCs) and of IFNα production upon stimulation. Upon in vivo deletion, a decrease in pDCs was only observed after subsequent in vitro expansion. This difference was likely related to insufficient replication-mediated loss of H3K79 methylation in vivo within the time frame studied. Transcriptomes of Dot1l-KO DC subsets exhibited enrichment of antigen presentation pathways, and MHC class II surface levels were up-regulated in pDCs. Mechanistically, inhibition of DOT1L linked the observed effects to its methyltransferase activity. Together, our data indicate that in DCs DOT1L differentially affects the development of canonical subsets and suppresses antigen presentation pathways.
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