MICROGLIAL LINEAGE SPECIES ARE EXPRESSED IN MAMMALIAN EPIDERMAL GROWTH FACTOR-GENERATED EMBRYONIC NEUROSPHERES

The epigenetic signals and progenitor cell species involved in progres sive neural maturation in the mammalian brain are poorly understood, A lthough these complex developmental issues can be examined in cultures of generative zone progenitor cells, analysis of signaling relationsh ips in complex progenitor cell systems requires the meticulous definit ion of the cellular complement at each developmental stage, The presen ce of microglia within the generative-zone cultures would further comp licate these developmental analyses, Utilizing the microglial markers Griffonia simplicifolia B-4 isolectin, carbocyanine dye-acetylated low density lipoprotein, F4/80, and Mac-1 we now report the presence of m icroglia within cultures of late embryonic murine epidermal growth fac tor-derived generative zone progenitor cells, Cytokine treatment of se rially passaged epidermal growth factor-generated neurospheres altered the phenotype of the microglia in culture, Macrophage colony-stimulat ing factor treatment promoted the expression of spindle-shaped microgl ia, whereas granulocyte-macrophage colony-stimulating factor treatment promoted the elaboration of flat and amoeboid microglia, Treatment wi th microglial-conditioned medium or 10% non-heat inactivated fetal cal f serum led to an increased complement of both phenotypes. Microglia c ould be generated from single isolated neurospheres, and there were di fferences in the number of microglial lineage species obtained from di stinct oligopotent progenitor cells, raising the possibility that a co mplement of this cellular lineage may be derived from a progenitor cel l present within the generative zones, These observations indicate tha t microglia are present within the generative zone progenitor cell sys tem, and this system thus represents an important experimental resourc e to examine the progenitor cell maturation and the origin of the micr oglial lineage. (C) 1996 Wiley-Liss, Inc.