Fig. 5.

Wnts differentially control the development of DA neurons by regulating precursor proliferation and the acquisition of a DA phenotype. Wnt-5a, but not Wnt-1, up-regulated the expression of Ptx3 mRNA (A) and c-ret mRNA (B) and maintained the expression of GDNF family receptor α1 (GFRα1) mRNA (C) and NCAM mRNA (D) at 3 days in vitro, as assessed by real-time RT-PCR in E14.5 rat VM precursor cultures. (E and F) Double immunocytochemistry revealed that Wnt-5a increased the percentage of TH+/Nurr1+ cells from 50% to 90%. Wnt-1 was less efficient than Wnt-5a, and Wnt-3a actually decreased the proportion of TH+ cells from 50% to 30%. (G and I) Fz8-CRD decreased, in a dose-dependent manner, the proportion of Nurr1+ cells that acquired TH expression in E14.5 VM precursor cultures, indicating that Wnt signaling is required for the acquisition of a DA phenotype. (H and I) Treatment of rat E14.5 VM precursor cultures with Fz8-CRD decreased the percentage of TH+/Nurr1+ cells after treatment with Wnt-5a. Statistical analysis and concentrations as in Fig. 4. (J) Model of the mechanisms by which Wnt-1, -3a, and -5a regulate the development of VM DA neurons. Wnt-3a, which is mainly expressed in the dorsal midbrain, enhances the proliferation of Nurr1-expressing precursors and decreases the proportion of neurons that acquire a DA phenotype. Wnt1, probably derived from the midbrain–hindbrain organizer, controls the proliferation of Nurr1-expressing precursors and increases the number of VM neurons. Finally, Wnt-5a increases the number of VM DA neurons specifically by regulating the acquisition of a DA phenotype in Nurr1-expressing precursors. Note that the size of the arrows correlates with the intensity of the effects.