Fig. 7. ß-galactosidase staining of mammillary body axonal projections in E11.5 Sim1/Sim2 mutant embryos. E11.5 brains with various genotypes, as indicated, were stained for ß-galactosidase activity and sectioned coronally. Axonal bundles (arrows) are easily recognizable in Sim1^tlz/+;Sim2^+/- (A) and in Sim1^tlz/+;Sim2^-/- (B) embryos, but are decreased in Sim1^tlz/-;Sim2^+/- embryos (C). No bundle was detected in Sim1^tlz/-;Sim2^-/- embryos (D). Note that axons progress in a domain that is stained. ß-galactosidase staining in the dorsal domain is weaker in C and D than in A and B because these thick sections (A,B) of early embryos are from a slightly different plane.