Figure 3.

Skn and Shh^C25S mutants exhibit defective short- and long-range signaling in the neural tube. (A-T) Isotopic in situ hybridization using ³³P-UTP-labeled riboprobes (pink) on paraffin sections of wild-type, Skn^-/-, Shh^C25S, and Shh^-/- 10.5-dpc embryos at the forelimb/heart level. The bottom left panel shows a schematic diagram of the expression domains of transcription factors, a combination of which define five progenitor cell types (Vp0, Vp1, Vp2, pMN, and Vp3) in wild-type embryos. As a result, five distinct neuronal types (v0, v1, v2, MN, and v3) are generated, which could be identified by neuronal-specific markers. In Skn mutants (bottom right panel) as well as in Shh^C25S mutants, reduced Hh signaling leads to loss of floor plate, v3, MN, and most v2 with concomitant changes in the progenitor domains. This phenotype is similar to that in Shh^-/- mutants perhaps with the exception of v2, a greater proportion of which is present in Skn and Shh^C25S mutants. Similarly, the Shh^C25S phenotype is slightly less severe than that in Skn mutants judged by residual v2. Expression of Islet1 in R-T represents neural crest-derived ganglia.