Fig. 4. A diffusible factor present in postnatal cortical slices can induce glial fates. (A) Diagrammatic representation of the assay used to evaluate the influence of cortex-derived diffusible factors on cell fate specification. Dissociated E15 cortical GFP cells were diluted 1:1000 with wild-type E15 cortical cells and plated on glass coverslips underneath membrane inserts containing either rat E18 or P15 cortical slices. After 5 DIV individual clones of GFP+ cells were classified as neuronal (B) or glial (C) by immunofluorescence with anti-GFP (green channel) and anti-MAP-2 (red channel) antibodies. (D) Quantification of the percentage of GFP+ clones that contained only neurons (filled bars), glia (open bars), and both neurons and glia (mixed clones; hatched bars) under indicated experimental conditions. Asterisks indicate statistically significant differences (P<0.05) between the experimental condition and control (medium) for the indicated clonal type. (E) Quantification of the average number of total GFP+ clones, the average number of neuronal, glial and mixed clones, and the average cell number in either neuronal, glial, or mixed clones under indicated experimental conditions (± s.e.m.). (F) Time-lapse images of the development of a GFP-positive clone between 4 and 7 DIV.