Targeted deletion of an Nr4a1­ associated enhancer ablates Ly6Clow monocytes while protecting pleiotropic gene function in macrophages [ChIP-seq]

Mononuclear phagocytes are a diverse cell family that occupy all tissues and assume numerous functions to support tissue and systemic homeostasis. Our ability to investigate the roles of individual subsets is limited by an absence of approaches to ablate gene function within specific sub-populations. Using Nr4a1-dependent Ly6Clow monocytes as a representative cell type we show that enhancer deletion addresses these limitations. Combining ChIP-Seq and molecular approaches we identify a single, conserved, sub-domain within the Nr4a1 enhancer that is essential for Ly6Clow monocyte development. Mice lacking this enhancer lack Ly6Clow monocytes but retain Nr4a1 gene expression in macrophages during steady state and in response to LPS. Nr4a1 is a key negative regulator of inflammatory gene expression and decoupling these processes allows Ly6Clow monocytes to be studied without confounding influences. Enhancer targeting possesses greater specificity than cre recombinase-mediated gene deletion, providing a route to generate loss-of-function models in closely related cell types.