Genome-wide screening identifies Trim33 as an essential regulator of dendritic cell differentiation [Hoxb8-FL ATAC-Seq]

The development of all dendritic cells (DCs) including antigen-presenting conventional DCs (cDCs) and cytokine-producing plasmacytoid DCs (pDCs) is controlled by the growth factor Flt3 ligand (Flt3L) and its receptor Flt3. We genetically dissected this common Flt3L-driven pathway of DCs differentiation using CRISPR/Cas9-based dropout screening in a Flt3L-dependent progenitor cell line. Genome-wide screening identified multiple regulators of DC differentiation including the glycosylphosphatidylinositol transamidase complex and arginine methyltransferase Carm1, whose role was confirmed in vivo. It also showed that negative regulators of mTOR signaling, including the subunits of TSC and GATOR1 complexes, restricted progenitor growth but enabled DC differentiation, demonstrating that a TSC- and GATOR1-mediated shutdown of mTOR is required for the process. An orthogonal screen focused on transcriptional regulators showed that Trim33 (TIF-1g) is required for DC differentiation. Conditional targeting in vivo revealed an essential role of Trim33 in the development of all DCs, but not of monocytes or granulocytes. In particular, inducible deletion of Trim33 caused a rapid loss of all DC progenitors, pDCs and the cross-presenting cDC1 subset. The loss of Trim33 from DC progenitors caused spontaneous interferon and inflammatory response, aberrant induction of macrophage-specific genes, and failure to induce DC differentiation program. Collectively, these data elucidate common mechanisms that control Flt3L-driven differentiation of the entire DC lineage, and identify Trim33 as its essential regulator.