Fig. 3. Early morphological changes and reduced cell proliferation in the Lmx1b^-/- embryo. (A,B) Nissl-stained sagittal sections of embryos at E10.5, showing the reduced rhombomere 1 (r1) and less conspicuous isthmus in the mutant brain (B, arrow), as compared with the control brain (A, arrow). (C,D) Immunostaining of Ki67, showing a reduced number of proliferating cells in the tectum and r1 of Lmx1b^-/- embryo (D) as compared with that in the control (C) at E10.5. (E-H) Sagittal sections of embryos at E12.5, showing the loss of the constriction between the midbrain and hindbrain (F, arrowhead) and reduced Math1 expression (E,F, arrows) in the presumptive cerebellum (H, arrow) in the mutant embryo, as compared with control brains (E,G). (I,J) Expression domain of Otx2 (arrow) did not show a caudal extension in Lmx1b^-/- mutant embryos (J) as compared with wild-type (I) at E12.5. (K,L) Transverse sections of embryos at E12.5, showing reduction of Nurr1 expression in the ventral midbrain of the mutant embryo (L) as compared with the control (K). (M-P) Transverse sections of embryos at E15.5, showing the loss of the cerebellar vermis (N, arrow) and normal Brn3a expression in the presumptive red nucleus (P, arrow) in the mutant embryos as compared with control brains (M,O). (Q,R) Transverse sections of embryo at E15.5, showing the loss of tyrosine hydroxylase (TH) immunostaining in the tegmentum of the mutant (R) as compared with the wild-type embryo (Q). Aq, aqueduct; Cb, cerebellum. Scale bars: A-D, 1000 µm; E-L, 700 µm; M-R, 500 µm.