Fig. 2. The precise anatomical correlation between ß-galactosidase staining, which reflects Pax6 in situ hybridization pattern, and the trajectory of the developing TCAs were studied in E14.5 (A-F) and E15.5 (G-I) Pax6^+/- brains. A single DiI crystal was placed into the dorsal thalamus (dt) (asterisk in F) of Pax6^+/- brains after they had been stained with ß-galactosidase. From the E14.5 brain, three adjacent serial sections were examined with light microscopy for ß-galactosidase expression, which appears green-blue (A-C), and with two filters of a fluorescent microscope to reveal the DiI-labelled thalamic fibres (red) and the bisbenzimide counterstaining (blue) on superimposed images (D-F). (D-F) The TCAs crossed the diencephalic-telencephalic boundary (E) and extended through the internal capsule (D). By E15.5 (G-I), labelled cells were observed in the internal capsule (arrow in H). (I) On the superimposed image of G and H, note that the ß-galactosidase staining extends lateral to the group of backlabelled internal capsule cells (arrow in I). ctx, cerebral cortex; GE, ganglionic eminences; PSPB pallial/subpallial boundary. Scale bars: 200 µm in A-F; 100 µm in G-I.