Fig. 3. Decreasing Fgf8 gene dose in mes/r1-S2GOF embryos results in absence of the vermis. (A,B) Dorsal views of brains collected from E17.5 embryos of the genotypes indicated. In the mutant brain, the region where the vermis would normally be found is indicated by a yellow asterisk. (C-E) Low-magnification views of midsagittal sections of E17.5 control and mes/r1-S2GOF;F8 mutants, stained with Cresyl Violet. (D,E) Examples of the group I (milder) and group II (more severe) brain phenotypes observed in the mutants. The broken red and yellow lines and red and yellow asterisks are explained in the legend to Fig. 2A,B,E,F. The areas outlined in C-E are shown at higher magnification in F-H, respectively. (F-H) High magnification views of basal structures. When present, nIII and nIV are circled with broken lines. (I-K) High magnification views of more lateral sagittal sections of the same brains, assayed by immunohistochemistry with an antibody against tyrosine hydroxylase, which specifically stains nuclei in the lateral posterior diencephalon, midbrain and anterior hindbrain. The broken red line indicates the boundary between diencephalon and midbrain. (L,M) Dorsal views of intact brains collected from P21 mice of the genotypes indicated, stained with ink. The broken line in L outlines the vermis, which is absent in the mutant brain. CbV, cerebellar vermis; CbH, cerebellar hemispheres; CP, choroid plexus; Di, diencephalon; IC, inferior colliculus; Is, isthmus; LoC, locus ceruleus; mlf, medial longitudinal fascicle; nIII, oculomotor nucleus; nIV, trochlear nucleus; PPT, posterior pretectal nucleus; SC, superior colliculus; SN-VTA, substantia nigra-ventral tegmental area.