They took the control of the sonic hedgehog expression of axolotl. They took it from the research done by Esther Schnapp, Martin Kragl, Lee Rubin and Elly M. Tanaka [reference no 13 in the provided paper]. In that paper [ref no13], they also discussed about transcription factors Pax6, Msx1, and Pax7 expression which are markers of dorsoventral neural progenitor cell populations. The provided paper [PMC4074850] is focused on the expression of shh in Xenopus larva. Solution They took the control of the sonic hedgehog expression of axolotl. They took it from the research done by Esther Schnapp, Martin Kragl, Lee Rubin and Elly M. Tanaka [reference no 13 in the provided paper]. In that paper [ref no13], they also discussed about transcription factors Pax6, Msx1, and Pax7 expression which are markers of dorsoventral neural progenitor cell populations. The provided paper [PMC4074850] is focused on the expression of shh in Xenopus larva..