Shh and Gli3 regulate formation of the telencephalic-diencephalic junction and suppress an isthmus-like signaling source in the forebrain

► HPE involves failed formation of the TDJ and ventricular collapse ► Genetic relations of Shh and Gli3 differ in the telencephalon and diencephalon ► Shh and Gli3 suppress an 'isthmus-like organizer' in the diencephalon ► Ectopic rings of Fgf8 and Wnt3a correlate with increased growth ► Ectopic Fgf8 and Wnt3a are unable to repattern the diencephalon