Fig. 2. Analysis of mes-met derivatives in Fgf8 loss of function mutants. (A-F) Analysis of midbrain, isthmus and cerebellum phenotypes at E17.5. (A,B) Lateral views of control embryos and MHB KO mutants at E17.5. The arrow in B points to the part of the head that is misshapen due to the absence of the midbrain and cerebellum. Note that craniofacial development appears normal in the mutant embryo. (A',B') Dorsal views of the brains from the embryos shown in A and B. (C-F) Paramedial sagittal sections of control, Fgf8^neo/neo, Fgf8^neo/null and MHB KO mutant brains at E17.5, stained with Cressyl Violet. The arrow in each panel points to the caudal limit of the posterior commissure, which marks the rostral limit of the midbrain. The bulk of the dorsal midbrain (tectum) is subdivided into the superior colliculus (rostral) and inferior colliculus (caudal). (C'-F') Lateral sagittal sections of the same brains, assayed by immunohistochemistry with an antibody against tyrosine hydroxylase, which specifically stains nuclei in the ventrolateral midbrain (tegmentum) and anterior hindbrain. The pontine nuclei are present in all samples, but are outside of the field in the control. (G-J) Embryos at E10.5, assayed by whole-mount immunohistochemistry with an anti-neurofilament antibody to label the cranial nerves and ganglia. III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve and ganglia; VII, facial nerve and ganglia; VIII, acoustic nerve and ganglia; Cb, cerebellum; CP, choroid plexus; Di, diencephalon; IC, inferior colliculus; LoC, locus ceruleus; Mb, midbrain; OB, olfactory bulb; PC, posterior commissure; PN, pontine nuclei; PPT, posterior pretectal nucleus; Pt, pretectum; SC, superior colliculus; SNC, substantia nigra pars compacta; Tel, telencephalon; VTA, ventral tegmental area.