Fig. 3. MTEG and MTT development affected by Sim1/Sim2 gene dosage. E18.5 brains of various genotypes were sectioned sagittally and stained with Haematoxylin. The upper panels (A-C,G-I) represent medial sections containing the PMT, whereas the lower panels correspond to lateral sections that include the MTT and the PMT. The MTEG is not readily detectable on sagittal sections because of its orientation. The PMT is indicated by arrows, the MTT by arrowheads. The PMT and MTT are well developed in Sim1^+/-;Sim2^+/- (A,D) and Sim1^+/+;Sim2^-/- (B,E) embryos, whereas they are thinner in Sim1^-/-;Sim2^+/+ (C,F), Sim1^+/-;Sim2^-/- (G,J) and Sim1^-/-;Sim2^+/- (H,K) embryos. The PMT and MTT were barely detectable in Sim1^-/-;Sim2^-/- embryos (I,L). In all cases, the MB was histologically present.