Fig. 4. The altered DARPP-32 expression detected by IHC in Gsh2 mutants is independent of ectopic Pax6. Foxp1, a marker of the developing striatal neurons during development (A), appears relatively normal in a Pax6 mutant striatum (C). The number of Foxp1-expressing cells (detected by IHC) is severely reduced in the Gsh2 mutant striatum (B), which is improved by removing Pax6 from the Gsh2 mutant background (i.e. in Pax6;Gsh2 double mutants) (D). Gsh2 mutants (F) exhibit a disproportionate reduction in the number of DARPP-32-positive neurons compared with wild type (E) and Pax6 mutants (G). Despite the improvement in striatal size in Pax6;Gsh2 double mutants, the number of DARPP-32-positive neurons remains disproportionately reduced (H), similar to that in the Gsh2 mutant (F).