In vivo parenchymal invasion of C6 glioma cells overexpressing the fusion protein GFP-Cx43. A, vimentin-immunolabeled C6 glioma cells (red) 8 days after striatal injection in the nude mice brain. C6 cells overexpressing the Cx43-GFP protein in green (arrow heads), are preferentially located at the tumor margin and display an invasive phenotype (×100). B, Microscopic field of the area boxed in A, at a higher magnificence (×200). C, D, confocal section (1 μm) of the border of another tumor showing invasive C6-Cx43-GFP cells at the tumor periphery migrating out. C6 cells which did not express Cx43-GFP protein, only labeled in red for vimentin remain in the tumor mass. E, is the overlay of the two channels. Migrating C6-Cx43-GFP cells appear yellow because of the merge of red and green. Dashed lines indicate the extremity of the tumor mass. Scale bar, 25 μm. tm, tumor mass.