Fig. 3. Expression of Hes1 and Hes5 in the dorsal telencephalic midline. (A) Scheme of a dorsal view of E12.5 forebrain. Coronal sections are made along the broken line. (B) Schemes of the coronal sections of the dorsomedial telencephalon at E10.5-E12.5. (C-F) At E10.5, the dorsal telencephalic midline expressed Bmp4 and Lmx1a (C,D). Hes1 was likewise expressed in this region as well as in the neighboring diencephalic and telencephalic neuroepithelium (E). Hes5 was expressed at a lower level in this region than in the telencephalic neuroepithelium (F). (G-N) At E11.5, the Bmp4 and Lmx1a expression domain was elongated (G,H). Msx1 and Ttr were expressed in differentiating choroid plexus epithelium (I,J), whereas Wnt2b was expressed in the prospective cortical hem (K). Hes1 expression was gradually downregulated in Ttr⁺ cells (L). Although Hes5 expression was upregulated in the telencephalon and the diencephalon, it was also downregulated in Ttr⁺ cells (M). Wnt2b⁺ and Msx1⁺ domains were clearly separated at this stage (N). (O-T) At E12.5, the choroid plexus epithelial cells became thin and cuboidal (R, Ttr⁺), whereas the cortical hem was still pseudostratified. Bmp4 and Lmx1a were expressed in both regions (O,P). Msx1 expression occurred mainly in the choroid plexus epithelium (Q), whereas Wnt2b expression occurred in the cortical hem (R). Hes1 and Hes5 expression was almost completely repressed in the choroid plexus epithelium (S,T). Scale bars: 100 µm in C-F; 200 µm in G-T.