The LCS stream is absent in E16.5 Emx1-cKO mice.

(A-J) Images and graphs represent E16.5 Emx1-cKO (cKO) and control (ctrl) mice. (A-C) Confocal images show coronal brain sections of mice carrying a Rosa26^CAG-LSL-tdT allele. Sections were immunostained for tdT, CC3, Ki67, Pax6, and Tbr2 as indicated. Arrows indicate the corticostriatal sulcus. Rectangles in (a.) indicate the region of interest for (b.) and (c.). Note increased number of CC3⁺ cells lateral and ventral to the corticostriatal sulcus in the cKO shown in (b.). Images in (c.) represent separate channels at low magnification (upper panel) and overlays at high magnification (lower panel). (D) Epifluorescence images show immunostaining for BLBP. Arrows indicate the corticostriatal sulcus. (E-G) Scatter plots show the number of CC3⁺ cells (e.), the density of Ki67⁺, Pax6⁺, and Tbr2⁺ cells (f.) as well as the overlap of Ki67, Pax6, and Tbr2 with tdT (g.). Measurements were performed in the tdT⁺ progenitor domain lateral and ventral to the corticostriatal sulcus highlighted in (a.). (H) Darkfield micrographs of coronal brain sections demonstrate Cxcl12 in the pallium of ctrl and cKO mice at a rostral and at a mid sectional plane. Arrows indicate the corticostriatal sulcus, arrowheads the Cxcl12⁺ SVZ, and asterisks the LCS. (I) Confocal images demonstrate BrdU⁺ cells in E16.5 mice receiving BrdU on E16. The LCS was photographed immediately ventral to the corticostriatal sulcus. Rectangles #1 and #2 represent dorsal (#1) and ventral (#2) parts of the LCS. (J) Scatter plots show the density of BrdU⁺ cells in regions #1 and #2. Horizontal lines indicate the median. Measurements and statistics are summarized in S1D Table. Abbreviations: CPu, caudate-putamen; LCS, lateral cortical stream; sCTX, somatosensory cortex. Scale bars: 180 μm (a.), 140 μm (b.), 180 μm (c. upper panel), 50 μm (c. lower panel), 200 μm (d. and h.), 100 μm (i.).