Pax6 regulates the expression domain of shh expression in the MDO in zebrafish. (A-H) Lateral views of wholemount ISH for shh in 28 hpf zebrafish embryos of the indicated experimental procedure. (A-D) red arrows mark the MDO, whereas red arrowheads mark the position of the reduced MDO. (A’,B’,C’,D’) show a coronal section of the prosencephalon with anterior to the bottom. hpf, hours post-fertilization; ISH, in situ hybridization; MDO, mid-diencephalic organizer.