Figure 7. Alteration of β-catenin signaling during late neurogenesis influences cell positioning and fate.

E15.5 embryos were electroporated with GFP (A, B, C) (N=4 brains) or Δ90β-cateninGFP (D, E, F)(N=4 brains) constructs. Embryos were analyzed at E19.5 and sections were stained for GFP and BRN1, a marker for cortical layers 2 to 4 (A,D) or FOXP2, a marker for cortical layers 5 and 6 (B,E). The fractions of GFP+ cells that co-expressed BRN1 were significantly different (p=0.0022, t-test, 2-tailed). Increasing β-catenin signaling by Δ90β-catenin-GFP decreased the fraction of BRN1+ cells (0.8983 ± 0.01558 ± s.e.m., n=206) when compared to control (0.9785 ± 0.002237 ± s.e.m., n=247). The fractions of GFP+ cells co-expressing FOXP2 were also significantly different (p=0.0397, t-test, 2-tailed). Increasing β-catenin signaling by Δ90β-catenin-GFP increased the fraction of FOXP2+ cells (0.07780 ± 0.01518 ± s.e.m., n=363) when compared to control (0.02693 ± 0.01214 ± s.e.m., n=148). The somal position of each electroporated cell within ten equal sized been bins covering the complete cortical plate was also noted. The fraction of the total GFP+ cells in each of the ten bins was then graphed (C, F) for both experimental conditions. Bin 1 corresponds to the section of the cortical plate closest to the pial surface, while Bin 10 is adjacent to the white matter tracts. Overall, cells electroporated with Δ90β-catenin-GFP (N=4, n=447) resided in slightly deeper cortical positions than GFP (N=4, n=280) control cells. When these results are shown in a cumulative view (G) the shift in positioning is more evident. Arrows highlight examples of FOXP2/GFP double positive cells. Arrowheads indicate GFP+/BRN1- cells. Scale bars are 100 μm.