Figure 2  Schematic showing the location of embryonic signaling centers at embryonic day (E) 10.5 in the mouse brain. The four families of secreted signaling molecules are positioned mainly at and near the midline region. In the telencephalon (Frontal view; A) the most prominent source of Fgf activity is positioned between the cortical hem (green; a source of WNT and BMP), and the ventral SHH source (yellow). As in the forebrain, the same or similar signaling molecules direct neural tube patterning and NSC development in the remainder of the CNS (B). (C), Dual probe in situ hybridization data exemplifying the schematic drawn in (A) in a mouse embryo at the age of E10.5. Abbreviations: tel, telencephalon; di, diencephalon; np, nasal processes.