Fig. 4. Wnt1 is necessary for terminal differentiation of Th-expressing mDA precursors. (A) Consecutive sagittal sections of wild-type and Wnt1^-/- embryos at E9.5 (n=8) hybridized with probes for En1 and Aldh1a1. (B) Sagittal sections of wild-type and Wnt1^-/- embryos at E11.5 (n=8) hybridized with En1 or immunostained for RC2 (a radial glia marker, red). (C) Fluorescent immunodetection of Th (green) and Pitx3 (red) on sagittal sections of wild-type and Wnt1^-/- mutant embryos at E11.5 (n=3). The white square in B corresponds to the region of the sections in C. Graph shows that the number of Th-positive cells was drastically reduced in the Wnt1^-/- mutant at this stage (mean±s.d./s.e.m. from three sibling pairs: wild type, 1958±129/92 cells; Wnt1^-/-,14±11/8 cells). Triple asterisks indicate numbers that differ at P<0.0024, paired t-test. (D) Schematic drawing of a cross-section through the E11.5 ventral midbrain of wild-type mouse embryos, suggesting a possible role of Wnt1 in the generation of Pitx3-expressing mDA neurons.