Fig. 4. Six3 is not necessary for the expansion or maintenance of the ZLI. (A) At E12.5, Six3 is normally expressed in the tegmentum, prethalamus and hypothalamus. (B-D) Shh, Lim1 and Ngn2 (arrows in B,C and D, respectively) expression reveal the location of the ZLI. Lim1 is also expressed in the pretectum and Ngn2 in the thalamus. (E) Dlx2 is another marker for the prethalamus. Similar analyses were performed in Six3^F/-;Six3-Cre (F-J), Six3^F/-;CAGG-CreERT2 (TM-induced at E9.5; K-O) and Six3^F/-;CAGG-CreERT2 brains (TM induced at E10.5; P-T). A similar efficiency of Six3 deletion was found in all three genotypes (F,K,P). As indicated by the expression of Shh (G,L,Q), Lim1 (H,M,R) and Ngn2 (I,N), the ZLI (arrows) was formed normally in these mutant mouse embryos. The thalamus, as indicated by Ngn2 expression (I,N,S), and the prethalamus, as shown by Dlx2 staining (J,O,T), were present in all of the conditional mutants. Asterisks indicate the telencephalon. Anterior is to the right. HY, hypothalamus; PT, prethalamus; PTC, pretectum; T, thalamus; TG, tegmentum.