Loss of Pax6 results in precocious formation and expanded expression of Shh in the MDO. (A-H) ISH for Shh and Ptch1 on coronal sections of E12.5 embryos of the indicated genotypes. (I and J) Wholemount ISH for Shh in control (I) and Pax6Sey/Sey(J) embryos at E9.5. Arrows denote the MDO; brackets show the expanded domain of Shh in the MDO; dashed line arrow indicates the dorsally (rostrally) and ventrally (caudally) expanded Ptch1 expression domains in F; the red arrowhead in J indicates the precocious induction of the ZLI Shh expression in Pax6Sey/Sey embryos. Scale bar in (A): 200 μm (A-H). E, embryonic day; ISH, in situ hybridization; MDO, mid-diencephalic organizer; ZLI, zona limitans intrathalamica.