Fig. 1. Extracellular signals in the cortex regulate neuronal and glial differentiation. (A,B) Dissociated E15 cortical GFP cells were cultured over rat E18 or P15 cortical slices for 5-10 days in vitro, and then processed for immunofluorescence to identify differentiated neurons and glia. Examples of E15 GFP cells growing over an E18 cortical slice after 5 days in vitro (A) or over P15 slice after 10 days in vitro (B). Cells growing over embryonic slices differentiated into MAP-2+ neurons with characteristic neuronal morphology (A), whereas cells growing on P15 slices differentiated into GFAP+ astrocytes with characteristic glial morphology (B). The white arrowhead in A identifies a neuron immunopositive for GFP (green channel) and the neuronal-specific dendritic marker MAP-2 (red channel; yellow on the merged image) while the yellow arrowhead in B identifies a glial cell immunopositive for GFP and the astrocyte specific marker GFAP. (C-F) Quantification of the number of GFP+ neurons (filled bars) and GFP+ glia (open bars) in slice overlay cultures from different developmental ages expressed as a percentage of the total number of GFP+ cells on top of the slice. The undefined population (hatched bars) were MAP-2- cells that failed to extend processes. Bar heights represent mean ± s.e.m.
