Fig. 3. SHH induces gene expression and proliferation in tectal explants. (A) Sketch of a lateral view of a P2 mouse brain showing the position of explanted tissue within the tectum. (B) RT-PCR analyses of gene expression in untreated control (con) or SHH-treated (+SHH) mouse P2 superior (SC) or inferior (IC) colliculi explants. Expression of Gli1 and Ptch1 is clearly upregulated. The low expression of Gli1 is barely detectable in the IC but is clearly seen after additional cycles. (C,D) Increase in the number of BrdU-positive cells in IC explants treated with SHH (C) when compared with an untreated IC explant (D). ps, pial surface; vs, ventricular surface. Seven independent explants were used for RT-PCR from each the IC and SC. (E) Quantification of cell proliferation by SHH treatment or inhibition of SHH signaling on P2 mouse IC explants. Numbers of cells±s.e.m. are given. n>10 sections of five independent explants counted for each condition.