Fig. 1. Spatial and temporal expression pattern of Shh, Gli1 and RGC differentiation. In situ hybridization for Shh and Gli1 mRNA and immunohistochemistry for Brn3b staining on serial sections of the mouse eye at E12 (A-C) and E13 (D-F). (A-C) Shh expression is initiated behind the leading edge of RGC differentiation, as marked by Brn3b staining (lines in B) at E12. (C) Gli1 expression is localized to the neuroblast layer overlying the Shh-expression domain. (D-F) By E13, the Shh and Gli expression domains have expanded across the retina, but still lag behind the leading edge of RGC differentiation (lines in E). Scale bar: 200 µm.