 Studies on the role of "Shh" signaling in the ZLI were difficult to study for many years, because mutants lacking expression have many developmental deficits including lack of a diencephalon.Explant and lineage-labeling experiments previously described aided in elucidation of the role of "Shh" and other genes in differentiation of these tissues.More recently, the mouse Shh;Gli3 double mutant was found to have an enlarged diencephalon with a ring of Fgf8 and Wnt in place of the ZLI, indicating a complex interaction between Shh and these genes at the ZLI.