Fig. 5. ß-galactosidase staining of mammillary body axonal projections in E14.5 Sim1/Sim2 mutant embryos. E14.5 brains of various genotypes were stained for ß-galactosidase activity and sectioned coronally. For each brain, four consecutive sections are shown, the most anterior being at the top of the figure. PMTs are indicated by arrows, whereas the abnormally targeted axons are indicated by arrowheads. The loss of Sim1 function is associated with a decrease of the PMT and the emergence of MB axons directed towards the midline. Sim2 also contributes to this phenotype, as the axonal abnormalities are more severe in Sim1^tlz/tlz;Sim2^-/- than in Sim1^tlz/tlz;Sim2^+/+ embryos.