Conditional Pax6 expression in Tis21-positive APs changes the fate of the BP progeny.

Dorsolateral telencephalon of tamoxifen-treated E14.5 Tis21–CreER^T2 heterozygous mice electroporated at E13.5 with control (A,C,D,F,H–J) or Pax6-expressing (B,C,E,F–J) plasmid (see Fig 2B). (A,B,D,E) Tbr2 (A,B) or Sox2 (D,E) immunofluorescence (white) and RFP fluorescence (red), combined with DAPI staining (blue), on coronal 50-μm vibratome sections. Insets show representative examples of RFP-positive nuclei (outlined by dashed yellow lines) that are either Tbr2 (A,B) or Sox2 (D,E)-positive (yellow arrows, see also main panels) or-negative (yellow arrowheads). (C,F) Quantification of Tbr2- and RFP-positive cells (C) or Sox2- and RFP-positive cells (F) in the cortical wall (total), VZ, and SVZ, expressed as percentage of all RFP-positive cells in the cortical wall (200-μm wide area), upon control (Con, white) and Pax6 (black) electroporation. (G–I) Daughter cell pair analysis. (G) Examples of daughter cell pairs derived from Pax6-electroporated APs. Tbr2 immunofluorescence (white) and RFP fluorescence (red) on 12-μm cryosections. (Top) Tbr2+/Tbr2+, (middle) Tbr2+/Tbr2–, (bottom) Tbr2–/Tbr2–; yellow arrowheads, Tbr2–; yellow arrows, Tbr2+; yellow dashed lines, daughter cell pair nuclei. (H) Quantification of AP-derived daughter cell pairs upon control and Pax6 electroporation. Blue, Tbr2–/Tbr2–; red, Tbr2–/Tbr2+; green, Tbr2+/Tbr2+. Control, 23 pairs; Pax6, 24 pairs. (I) Distance of nuclei of the Tbr2–/Tbr2– daughter cell pairs from the ventricular surface upon control (Con, open circles, 7 pairs) and Pax6 (filled circles, 15 pairs) electroporation. Data indicate the position of the ventricular-most nucleus of each pair (see Materials and Methods). Light and dark blue background indicates ventricular (within <27 μm from the ventricular surface) and abventricular (≥27 μm from the ventricular surface) location, respectively. (J) Number of nuclei in the VZ (200-μm-wide area) upon control (Con, white) and Pax6 (black) electroporation. (A,B,D,E,G) Dashed white lines, ventricular surface. Scale bars, 20 μm; inset scale bars, 5 μm. (C,F,H,I,J) Mean of three independent experiments, each being the average of two to four embryos. Error bars, SEM. * p <0.05, ** p <0.01.