The phenotypic and functional properties of mouse yolk-sac-derived embryonic macrophages

Dev Biol. 2018 Oct 1;442(1):138-154. doi: 10.1016/j.ydbio.2018.07.009. Epub 2018 Jul 30.


Macrophages are well characterized as immune cells. However, in recent years, a multitude of non-immune functions have emerged many of which play essential roles in a variety of developmental processes (Wynn et al., 2013; DeFalco et al., 2014). In adult animals, macrophages are derived from circulating monocytes originating in the bone marrow, but much of the tissue-resident population arise from erythro-myeloid progenitors (EMPs) in the extra-embryonic yolk sac, appearing around the same time as primitive erythroblasts (Schulz et al., 2012; Kierdorf et al., 2013; McGrath et al., 2015; Gomez Perdiguero et al., 2015; Mass et al., 2016). Of particular interest to our group, macrophages have been shown to act as pro-angiogenic regulators during development (Wynn et al., 2013; DeFalco et al., 2014; Hsu et al., 2015), but there is still much to learn about these early cells. The goal of the present study was to isolate and expand progenitors of yolk-sac-derived Embryonic Macrophages (EMs) in vitro to generate a new platform for mechanistic studies of EM differentiation. To accomplish this goal, we isolated pure (>98%) EGFP+ populations by flow cytometry from embryonic day 9.5 (E9.5) Csf1r-EGFP+/tg mice, then evaluated the angiogenic potential of EMs relative to Bone Marrow-Derived Macrophages (BMDMs). We found that EMs expressed more pro-angiogenic and less pro-inflammatory macrophage markers than BMDMs. EMs also promoted more endothelial cell (EC) cord formation in vitro, as compared to BMDMs in a manner that required direct cell-to-cell contact. Importantly, EMs preferentially matured into microglia when co-cultured with mouse Neural Stem/Progenitor Cells (NSPCs). In conclusion, we have established a protocol to isolate and propagate EMs in vitro, have further defined specialized properties of yolk-sac-derived macrophages, and have identified EM-EC and EM-NSPC interactions as key inducers of EC tube formation and microglial cell maturation, respectively.

Keywords: Angiogenesis; Endothelial Cells; Macrophages; Microglia; Neural Stem/Progenitor Cells; Yolk sac.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Culture Techniques / methods
  • Cell Differentiation / physiology
  • Coculture Techniques / methods
  • Erythroid Precursor Cells / physiology*
  • Flow Cytometry / methods
  • Hematopoietic Stem Cells / physiology
  • Macrophages / cytology
  • Macrophages / physiology*
  • Mice / embryology
  • Myeloid Progenitor Cells / physiology*
  • Phenotype
  • Yolk Sac / cytology