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. 2023 Aug 18;8:315. doi: 10.1038/s41392-023-01559-5

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© The Author(s) 2023

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 1 — Activation and spread of hedgehog ligands in secretory cells. The three vertebrate hedgehog ligands Shh, Dhh and Ihh have similar secretion processes, differing slightly in the tissue distribution of the three. The figure shows the secretion of Shh as an example of the secretion process of hedgehog ligands. Activation of Shh occurs in the endoplasmic reticulum (ER). The Shh precursor is first processed into two parts, Shh-N and Shh-C. The carboxyl terminus of Shh-N is bound to cholesterol by a protein hydrolytic cleavage process, while the amino terminus of Shh-N is bound to palmitic acid mediated by Hhat. In contrast, Shh-C is degraded after being transported out of the ER. There are several mechanisms for the diffusion of Shh-N out of secretory cells after activation: a Shh-N is mainly transported out of secretory cells by the synergistic action of Disp1 and Scube2. b The polymerization of monomer-activated Shh-N into multimolecules facilitates the diffusion of ligands. c Hspg is localized to the secretory cell membrane, which recruits lipoprotein. Shh-N is loaded on the lipoprotein as a "passenger" for long-distance transportation. d Ptch1 on the surface of the receiving cells has a negative feedback regulation on the release of Shh-N