Bcl6, Irf2 and Notch2 promote nonclassical monocyte development [RNA-seq]

Ly6Clo monocytes are a myeloid subset that specializes in the surveillance of vascular endothelium. Ly6Clo monocytes have been shown to derive from Ly6Chi monocytes. Notch2 signaling has been implicated as a trigger for Ly6Clo monocyte development, but the basis for this effect is unclear. Here, we examined the impact of Notch2 signaling of myeloid progenitors on the development of Ly6Clo monocytes in vitro. Notch2 signaling induced by delta-like ligand 1 (DLL1) efficiently induced the transition of Ly6Chi TremL4– monocytes into Ly6Clo TremL4+ monocytes. We further discovered two additional transcriptional requirements for development of Ly6Clo monocytes. Deletion of Bcl6 from myeloid progenitors abrogated development of Ly6Clo monocyte development. IRF2 was also required for Ly6Clo monocyte development in a cell-intrinsic manner. DLL1-induced in vitro transition into Ly6Clo TremL4+ monocytes required IRF2 but unexpectedly could occur in the absence of Nur77 or Bcl6. These results imply a transcriptional hierarchy for these factors in controlling Ly6Clo monocyte development. Comparison of RNA expression in cMoPs and Ly6C+ classical monocytes which were cocultured with either OP9 or OP9-DLL1 cells for 6 hours.