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. Author manuscript; available in PMC: 2020 Sep 1.
Published in final edited form as: Semin Cell Dev Biol. 2018 Nov 14;93:153–163. doi: 10.1016/j.semcdb.2018.10.009

Figure 2.

Figure 2.

Most popular systems for the studies of Hh signaling

(A) The wing imaginal disc in Drosophila. Hh is transcribed only in the posterior compartment, and form a gradient in the anterior compartment. The highest level of Hh signaling induces En expression immediately adjacent to the compartment boundary. An intermediate level of Hh signaling induces Ptc expression, and a lower level of Hh signaling induces Dpp expression, in cells further anterior in the A compartment. A: anterior; P: posterior; D: dorsal; V: ventral.

(B) The vertebrate neural tube. Shh is produced in the notochord (nc) and floor plate (FP), and forms a ventral-to-dorsal gradient. Decreasing concentrations of Shh are required to determine the fates of the V3 interneurons, motor neurons (MN), V2 and V1 interneurons.

(C) The vertebrate limbs. Shh is expressed in the posterior mesenchyme known as the zone of polarizing activity (ZPA), and regulates digit formation by antagonizing Gli3 repressor activity. Wild type (wt) mouse limbs have five digits. Shh mutant limbs have only one digit. Gli3 mutant limbs have 8–9 identical digits. A: anterior; P: posterior; P: proximal; D: distal.