Figure 1

Dynamic changes in Shh and Gli1 expression in the ventral mesencephalic neural tube. RNA in situ hybridization with Shh, Gli1 and Lmx1a RNA probes. The analysis was performed on transverse sections (E8.5) or coronal sections of the mesencephalon (mes; E9.5 to E12.5); sections shown are at the level of the intermediate mes. V, ventral; D, dorsal. The mesencephalon is outlined. (A-E) Shh is initially expressed in the notochord (NC) and is induced in the mesencephalon floor plate (FP) at E8.5. Shh expression expands laterally over the subsequent days of development (E9.5 to E12.5), but is downregulated medially (E10.5 to E12.5). (F-J) At all time points analyzed, Gli1 expression, a readout for high levels of Shh signaling, is located laterally to the Shh- expressing cells. Gli1 expression is largely absent in the Shh-expressing domain, indicating that Shh- expressing cells do not respond to high level Shh signaling. At E9.5, the weak ventral expression domain of Gli1 and the weak lateral expression domain of Shh appear to overlap partially (B',G', asterisks), but at later stages, the Shh and Gli1 domains are clearly separated. Note that Gli1 expression is not upregulated in medial cells that downregulate Shh expression. (K-N) Lmx1a is expressed in the DA precursor domain and in differentiating DA neurons. Scale bars: (A,F) 50 μm; (B-E,G-J,K-N) 100 μm.