Fig. 4. In mouse, Trk receptor signaling regulates embryonic cortical precursor cell proliferation but not survival in vivo. (A-E) Cortices were electroporated with EGFP and the empty vector (control), dnTrkB and/or dnTrkC and analyzed 1-3 days later. (A) Confocal micrographs of coronal sections through cortices immunostained for EGFP (GFP, green) and cleaved caspase 3 (casp 3, red) at 1 day. The right panels show the merges. Arrows indicate transfected, cleaved caspase-3-positive cells, and arrowheads cells that only express cleaved caspase 3. (B) Quantification of the total number of EGFP-positive cells in six sections through electroporated cortices at 3 days. n=at least nine animals per group. (C) Confocal micrographs of coronal VZ/SVZ sections immunostained for EGFP (GFP, green) and Ki67 (red) at 3 days. The right panels show the merges. Arrows indicate transfected, Ki67-positive cells. (D,E) Quantification of the percentage of transfected, Ki67-positive cells in sections like C, at 1 or 3 days post-electroporation. For D, n=at least three embryos. For E, n=at least ten embryos, four to five sections/embryo at each timepoint. (F,G) Quantification of the percentage of transfected, Ki67-positive (F) or phospho-histone-H3-positive (G) cells in the VZ/SVZ of cortices transfected with EGFP and control shRNA (control) or one of two TrkB shRNAs (shTrkB-1, shTrkB-2) at E13/14 and analyzed 3 days post-electroporation. n=at least four, five to six sections/embryo. Error bars indicate s.e.m. Scale bars: 100 µm. ^*P<0.05, ^**P<0.01, ^***P<0.001 relative to control-transfected sections.