Fig. 6. Cells that failed to be GABAergic neurons are present in the midbrain of Mgn^tZ/tZ embryos. (A,B,D,E) Immunohistochemical staining of activated caspase 3 in the mesencephalic vesicle at E12.5. In the mesencephalic vesicle, no increase in apoptosis can be observed in the mutant. Single cells could be found labelled in the wild-type (Mgn^+/+) (A,B) as well as in the mutant (Mgn^tZ/tZ) in this region (D,E). (C,F) Immunohistochemical staining of NeuN in the developing SC at E13.5. There are no alterations in the thickness of either the ventricular zone or the mantle zone in the mutant mice (F). (G-J) No differences are observed in the PH3-positive cells in the wild-type (G, magnified in H) when compared with the homozygous mutant (I, magnified in J). (K-P) lacZ expression of E13.5 mouse Mgn^+/tZ (K-M) and Mgn^tZ/tZ (N-P) embryos. Whole-mount lacZ expression is more intense in the Mgn^tZ/tZ mice (N), whereas localization is identical to that in Mgn^+/tZ mice (K). lacZ expression in a coronal section of the SC from Mgn^+/tZ (L) and Mgn^tZ/tZ (O) embryos at E13.5. (M,P) Horizontal sections of the SC are magnified, showing single cells migrating out from the SVZ into the differentiation zone (arrows).