Fig. 7. Gli1 induces hyperplasia in the CNS of frog embryos. (A) Histological appearance of a Gli1-induced hyperplasia at the level of the hindbrain after sectioning and staining with Hematoxylin and Eosin. The unilateral development of hyperplasia is a consequence of the injection of Gli1 RNA into one cell at the two-cell stage, using the uninjected half of the brain as internal control. (B) Section of a Gli1-injected embryo showing the ectopic differentiation of HNF-3ß-positive cells within the hyperplastic region at the level of the midbrain. (C) Lineage tracing of a GLI1-induced hyperplasia in the neural tube. The section shows X-gal staining, indicating the development of a tumor from cells inheriting the co-injected GLI1 and lacZ RNAs. (D) Analyses of BrdU incorporation in a GLI1-injected embryo showing a large increase in the number of BrdU-positive cells in the hyperpastic side (arrows) versus the uninjected, control side. (E,F) Endogenous expression of Pdgfr
mRNA in the midventricular zone of the diencephalon (E), and its ectopic expression within the CNS hyperplasia of a Gli1-injected embryo (F). (G,H) Constitutive expression of endogenous Gli1 mRNA in hyperplastic regions (G, spinal cord; H, hindbrain) induced by injected human GLI1. (I,J) Hyperplasia resulting from the of injection of human GLI1 RNA (I) or it complete absence after injection of GLI1 RNA plus morpholino oligonucleotide anti-frog Gli1. X-Gal-stained cross sections are shown. The distribution of X-gal-labeled cells in J is as expected for animal pole injection. n, notochord; ov, otic vesicle; s, somites. All panels show representative cross sections of embryos at stages 
34-38 except A, which show sections of embryos at stage 40. Arrows indicate induced CNS hyperplasia and/or sites of gene expression within them. Broken lines show the axis of normal bilateral symmetry. The CNS and notochord are independently outlined. The size of the notochord in all sections serves as scale. fp, floor plate; n, notochord; s, somite; v, ventricle; v', secondary ventricle.
