Figure 5.

β-Catenin signaling influences the laminar cell fate of upper-layer cortical projection neurons. E13.5 embryos were electroporated with Δ90β-catenin-GFP (n = 4 brains), DNTCF4-GFP (n = 3 brains) or GFP (n = 4 brains) constructs. A–F, Embryos were killed at E19.5 and sections were stained for GFP and BRN1 (A–C) or SATB2 (D–F), markers for cortical layers 2–4. G, Fractions of GFP⁺ cells that coexpressed BRN1 in the three experimental groups were significantly different (p = 0.0004, ANOVA; Newman–Keuls post-test analysis: Δ90β-catenin-GFP vs DNTCF4-GFP, p < 0.001, Δ90β-catenin-GFP vs GFP, p < 0.01, DNTCF4-GFP vs GFP, p < 0.05). H, SATB2 expression was also significantly different among the three groups (p = 0.0013, ANOVA; Newman–Keuls post-test analysis: Δ90β-catenin-GFP vs DNTCF4-GFP, p < 0.01, Δ90β-catenin-GFP vs GFP, p < 0.05, DNTCF4-GFP vs GFP, p < 0.05). Increasing β-catenin signaling by Δ90β-catenin-GFP decreased the fraction of BRN1⁺ cells (0.267 ± 0.034, n = 255) and SATB2⁺ cells (0.304 ± 0.013, n = 117), while blocking β-catenin signaling increased the fraction of BRN1 (0.740 ± 0.017, n = 351) and SATB2 (0.817 ± 0.041, n = 232), when compared to GFP control (BRN1: 0.534 ± 0.065, n = 634; SATB2: 0.577 ± 0.079, n = 453). Arrows in insets (A′, A″, B′, B″, C′, C″) denote BRN1⁺ cells; arrowheads denote BRN1-. Arrows in insets (D′, D″, E′, E″, F′, F″) denote SATB2⁺ cells; arrowheads denote SATB2⁻ cells. The top panel for each inset shows BRN1 or SATB2 immunofluorescence, while the bottom panels show merged images. *p < 0.05, **p < 0.01, ***p < 0.001. Scale bars: main panels, 100 μm; insets, 25 μm. Brackets on graphs show SEM. EPed, Electroporated.