Fig. 6. The proliferating activity of mesDA progenitors is enhanced in Otx2 overexpressing mutants. (A-F) Representative adjacent sections through the intermediate mesencephalon of tOtx2^bov/+ (A,B), En1^Cre/+; tOtx2^ov/+ (C,D) and En1^Cre/+; tOtx2^ov/ov (E,F) embryos pulsed with BrdU for 30 minutes at E10.5 or E11.5, are immunostained with BrdU and Nkx6.1, and stained with Hoechst to determine the LI of progenitors in the mesDA and Nkx6.1 domains. The arrow and the broken line indicate approximately the Nkx6.1⁺ domain analyzed. (G-J) Graphic representation of the LI detected along the mesDA (G,H) and the Nkx6.1⁺ (I,J) domains shows a selective dose-dependent increase in the proliferating activity of mesDA progenitors developing in the intermediate and posterior mesencephalon. Abbreviations: Ant., anterior; Int., intermediate; Post., posterior.