Fig. 3. Constitutive expression of MUK arrests cells at the subventricular/intermediate zone. (A) The telencephalic region in a sagittal section of a paraffin wax-embedded E16 embryo stained with Hematoxylin and Eosin, representing the ventricular zone (VZ), intermediate zone (IZ) and cortical plate (CP). (B) The adenovirus vector of lacZ was injected into the lateral ventricle of an E13 embryo and frozen sections of the head were prepared three days later, at E16. lacZ activity was detected by X-gal staining (light blue). The arrow indicates the accumulation of lacZ-expressing cells in the cortical plate. (C) BrdU was injected intraperitoneally into an E13-timed pregnant mouse and the embryo was fixed at E16. Paraffin wax-embedded sections of the head of the embryo were stained with anti-BrdU antibody, alkaline phosphatase-conjugated secondary antibody and BM purple. The arrow indicates the accumulation of BrdU-labeled nuclei in the cortical plate. (D) An adenovirus vector of T7-MUK was injected into the lateral ventricle of an E13 embryo and paraffin sections of the head were prepared 3 days later, at E16. Cells expressing T7-MUK were detected by immunostaining with anti-T7 antibody. The arrow indicates a cell layer accumulating T7-MUK expressing cells in the intermediate zone. (E) The adenovirus vector of T7-MUK/KR was injected and cells expressing T7-MUK/KR were detected as in D. The arrow indicates the accumulation of T7-MUK/KR expressing cells on the pial side of the cortical plate (CP). (F) A paraffin wax-embedded section prepared from a non-injected E16 embryo was immunostained as in D,E to show the background level of staining with anti-T7 antibody. (G) An adenovirus vector of T7-MUK was injected as in D, and sections were prepared at E18 for the detection of T7-MUK by immunostaining using anti-T7 antibody. The arrow indicates the remaining T7-MUK-expressing cell layer in the intermediate zone (IZ). (H) An adenovirus vector of T7-MUK was injected into the lateral ventricle of an E15 embryo and paraffin wax-embedded sections of the head were prepared three days later, at E18. The arrow indicates the T7-MUK-expressing cells accumulated in the intermediate zone (IZ). (I-K) Adenovirus vectors for T7-MUK or T7-MUK/KR were injected into the lateral ventricle of an E13 embryo. The virus-injected embryos and non-injected control embryo were fixed at E14, and paraffin wax-embedded sections were immunostained using anti-T7 antibody. Cell layers corresponding to the ventricular zone (VZ) and preplate (PP) are indicated on the left. Note the wide distribution of expression of T7-MUK and T7-MUK/KR in cells in the ventricular zone. Scale bars: 200 µm.