Figure 3.

The septum expands in the Lhx2 mutant. (A and D) In control brains at E12.5, Emx1 (A) and Ngn2 (D) are expressed in the pallium (dorsal telencephalon), their expression extending medially to include the pallial septum. (B) Six3 is expressed in the subpallial component of the septum and also in the subpallium (E). Zic2 is expressed in both components of the septum and also adjacent medial pallial regions. In Lhx2 mutant brains, Emx1 and Ngn2 expression recedes from the medial telencephalon, whereas Zic2 and Six3 expression expand to fill this territory (A, B, D, E), as seen in false-color overlays of adjacent sections showing Emx1/Six3 (C) and Ngn2/Zic2 (F) expression. Ngn2 and Zic2 expressions overlap in the cortical hem (F and H). Arrowheads in A, B, and C mark the dorsal limit of the septum and the beginning of the Emx1-expressing domain (A) in control and Lhx2 mutant sections. (G) Fgf17 is expressed in both pallial and subpallial components of control septum shown at E11.5 and E12.5. In Lhx2 mutant, Fgf17 expression expands dorsally (arrowhead), while its ventral limit remains normally positioned (open arrowhead). (H) Schematic of Lhx2 mutant section at level “i” of Figure 1F, showing the extent of the expanded septum (s) and hem (h). (I) Area occupied by the septum is significantly increased in Lhx2 mutant brains compared with that of control brains (*P < 0.01). Scale bar: 300 µm.