Macrophage colony-stimulating factor (CSF-1) regulates the differentiation, proliferation, and survival of cells of the mononuclear phagocyte system. The activity of CSF-1 is mediated by the CSF-1 receptor (CSFlR, CD115) that is encoded by c-fms(Csf1r) protooncogene. The c-fmsgene is expressed in macrophage, trophoblast cell lineages, and to some extent granulocytes. A reporter gene construct containing 3.5-kb of 5′ flanking sequence and the downstream intron 2 of the c-fmsgene directed expression of enhanced green fluorescent protein (EGFP) to cells expressing the c-fmsgene including the macrophages and trophoblasts. EGFP was detected in trophoblasts from the earliest stage of implantation. During embryonic development, EGFP expression highlighted the large numbers of c-fmspositive macrophages in most organs. These embryonic macrophages contribute to organogenesis and tissue remodeling. In adult c-fmsEGFP transgenic mice, which have been called theMacGreenmice, EGFP expressed in all tissue macrophage populations and permitted convenient detection of tissue macrophages as well as facilitates their isolation from various tissues.
