Figure 7.

Sox4 is present in the SVZ and affects IPCs. A, Sox4 is coexpressed with the SVZ marker Tbr2 at E14.5; >75% of Tbr2⁺ cells are also Sox4⁺. B, C, Elevation of Sox4 results in increased Tbr2⁺ transfected cells, whereas reduction of Sox4 reduced Tbr2⁺ transfected cell number. D, E, G, E12.5 control or Sox4^CKO mouse cortex stained with Sox9, a marker of apical progenitors, or Tbr2, a marker of IPCs, reveals no change in Sox9⁺ but decreased Tbr2⁺ cells in the Sox4 mutant cortex. F, H, Phospho-histone-H3 staining of control or Sox4^CKO mouse cortex reveals decreased basal but not apical progenitors. I, Coimmunoprecipitation using E14.5 cortical lysate in which antibodies for Sox4 or Sox11 or a control IgG was used to pull down before Western blotting was performed with antisera specific for Ngn2 or Tbr2. Sox4 preferentially binds Ngn2 and Tbr2 compared with Sox11. J, The Tbr2 locus, with genomic organization mapped above and levels of conservation between mouse and human indicated by the height of the peaks beneath. The promoter is magnified in the gray box, with possible Ngn (black), Sox (red), and Tbx (blue) sites indicated. Regions 1–3, studied with ChIP, are indicated by bars beneath. K, ChIP using E14.5 cortical lysate and primers specific for proximal (1), middle (2), and distal (3) regions of the Tbr2 promoter (bars in J) reveals that Sox4 is capable of binding to region 3, but not 1 or 2, of the Tbr2 promoter. L, M, Transactivation studies reveal that Sox4 alone activates the Tbr2 promoter and that this activation is maintained when Sox4 and Ngn2 are cotransfected. In contrast, transfection of Tbr2 does not affect levels of the Tbr2-driven luciferase alone, but Tbr2 and Sox4 together significantly increase the level of Tbr2 expression. Scale bars: A, 24 μm; B, 17 μm; D–F, 19 μm.