Cell type-specific development of rodent central nervous system progenitor cells in culture

Object. The aim of the study was to assess the pluripotential central nervous system (CNS) progenitor cells that give rise to the many differentiated neuronal and glial cell types of the adult mammalian brain and the role of peptide growth factors such as the epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF). The action of these factors is crucial to the survival and ultimate differentiation of these CNS progenitor cells. However, the precise role of EGF and bFGF in the time course of cellular development, the acquisition of cell type specificity, and possible differential mitogenic behavior has not been clearly defined. Methods. The authors defined the time course of CNS progenitor cell development in cultured embryonic rodent cells by using immunocytochemical analysis to identify the expression of pluripotential (nestin)-, neuron (microtubule-associated protein-2 [MAP-2])-, and glia (glial fibrillary acidic protein [GFAP])-specific proteins in response to treatment with EGF and bFGF alone or in combination. The bromodeoxyuridine (BUdR) labeling index for each treatment group was used to define the mitogenic effects of each growth factor. In this investigation, the authors observed that progenitor cells develop in a stereotypical fashion when exposed to bFGF or EGF. Marked staining for nestin was evident soon after plating. This declined over time as staining for MAP-2 and GFAP increased. When treated with EGF alone, cells maintained their nestin immunoreactivity longer than those treated with bFGF alone or in combination with EGF. Treatment with bFGF alone promoted a significant increase in MAP-2 and, to a much lesser extent, GFAP reactivity. This was observed concomitant with the decline in nestin staining. The BUdR labeling index was similar among the different treatment groups and declined similarly over time in all treatment groups. Conclusions. The effects of EGF and/or bFGF on the expression of development-and lineage-specific markers likely reflect the specific effects of these factors on developmental processes. These data indicate that bFGF exerts a preferential effect on neuronal development and, to a lesser extent, glial development, which is not explained by selective mitogenicity. The persistence of nestin staining seen in the cells treated with EGF alone indicates that EGF may function as a stem cell survival factor. This study provides evidence that CNS cell type-specific development can be altered by the manipulation of peptide growth factors that act as differentiation agents.