Fig. 1.

Ventralization of the neuroepithelium at the pallio/subpallial border at stage E12.5 in the Sey/Seytelencephalon. Adjacent coronal sections from the brain of wild-type (WT; A–D; F,H; E, G) and homozygous (Sey/Sey;A′–D′; F′,H′; E′, G′) littermates at E12.5 were hybridized with RNA probes for region-specific markers as indicated. The empty arrowhead inA points to the morphological corticostriatal sulcus, whereas the arrows in A,C, D, and E,H point to the pallial/subpallial border.A, The region of the ventral pallium is located between the arrowhead and the arrow (also in Figs. 5, 7). The thin arrows in A and A′) point to early-born Pax6+ cells possibly generated from the VP and migrating toward the presumptive anlage of the piriform cortex and anterior amygdala. B, B′,Emx1 is dorsally retracted from the LP in the mutant as compared with the WT brain. The subpallial markers for the VZ–SVZ are ectopically expressed in the Ne of the VP, LP, and DP of theSey/Sey as illustrated for: Dlx1(C′), Vax1 (D′), andMash1 (G′). The arrowheadsin C′ and D′ point to the extension of the Dlx1 and Vax1 expression into a more dorsal domain within the septum in the mutant brain. InH′, note that the normal expression ofSix3 in the striatal mantle extends laterally into the mantle of the VP. In E and E′, note that Ngn2 expression is abolished in the VZ of the VP, strongly suppressed in the LP and in a part of the DP, but appeared unaffected in the MP (designated by the asterisk below the MP). The two arrowheads in F point to the medial limit of Tbr1 expression along the pallial/subpallial border, thus including in its expression domain the mantle zone of the VP (the anlage of the ventromedial claustrum;Puelles et al., 1999). The expression of Tbr1 in this domain is abolished in the Sey/Sey brain (F′).