Fig. 1. Differential effects of Shh- or ActSmo-expressing retroviruses on brain morphology. Animals were infected in utero with control virus (A,B) and viruses expressing ActSmo (C,D) or Shh (E,F). Injections were performed at E8.5 (A,C,E) or E9.5 (B,D,F) and analyzed 4 days later (E12.5 or E13.5, respectively). Embryos injected with Shh virus showed a dramatic increase in the size of their heads, with substantially enlarged telencephalic vesicles (E,F). Despite the fact that the ActSmo virus was injected at a 10-fold greater titer than Shh virus, heads from these embryos appeared to have largely normal morphology (C,D).