Figure 6. Shh is required for the normal organization of thalamic progenitor domains. Frontal sections of Nes Cre /+ ; Shh c/c forebrain ( F–J ) and Nes Cre /+ ; Shh c /+ controls at E12.5 ( A–E ). Midline is to the left. Shh is expressed in the ZLI of control embryos ( A , arrow) but not in the Nes Cre /+ ; Shh c/c mice ( F , arrow). Olig3 expression is maintained in Nes Cre /+ ; Shh c/c embryos, but the domain is smaller and density of Olig3-positive cells in this domain also seems reduced ( F ). Gli1 , a target gene of Shh signaling, is lost in the thalamic progenitor cells of Nes Cre /+ ; Shh c/c embryos ( G ), while it is expressed in a graded manner in the control ( B ). Expression of Nkx2.2 and Olig2 is found in controls ( C , arrow for Nkx2.2, double arrows for Olig2), but is completely lost in Nes Cre /+ ; Shh c/c embryos ( H ). A reduced number of Olig2-expressing cells are still found in the prethalamus ( C , H , arrowhead). Mash1 expression in the pTH-R domain is detected in the control but is lost in Nes Cre /+ ; Shh c/c embryos ( D , I , arrowhead). Mash1 expression in the posterior pretectum is maintained ( D , I , arrow). Expression of Ngn2 is intact and now occupies the entire thalamus, including the most rostroventral region ( I , arrowhead). Dbx1 expression is limited to the rostral pretectum and caudodorsal part of pTH-C in control embryos ( E ). The expression domain of Dbx1 is expanded rostroventrally in Nes Cre /+ ; Shh c/c embryos ( E , J , arrow). Scale bar, 200 µm.