Characterizing Axonal Guidance Molecules in Regenerating Tissues of the Sea Cucumber Holothuria glaberrima

Successful organ regeneration depends on coordinated cell-to-cell communication mediated by ligand–receptor interactions that regulate proliferation, differentiation, and axonal guidance. Sea cucumbers, particularly Holothuria glaberrima, exhibit remarkable regenerative capacity following evisceration, regenerating their complete intestinal system within weeks. To identify molecular signals orchestrating these events, we characterized five ligand–receptor groups of axonal guidance molecules (Netrin/UNC5-DSCAM, Ephrin/Eph receptors, Semaphorin/Plexin, RGMα/Neogenin, and SLIT/ROBO) using transcriptomic databases from regenerating intestines and the radial nerve cord. Comparative analyses confirmed these as highly conserved orthologs, retaining characteristic structural domains essential for guidance signaling. Multiple alternatively spliced isoforms were detected, with tissue-specific variants suggesting functional diversification. Differential gene expression analysis across intestinal regeneration stages (12 hours to 21 days post-evisceration) revealed distinct temporal patterns: Netrin-1 showed significant upregulation at 7–14 days post-evisceration, coinciding with nerve fiber invasion into the intestinal anlage, while the Ephrin, Semaphorin, and SLIT–ROBO pathways exhibited late-stage expression associated with luminal tissue formation. Single-cell RNA sequencing from 9-dpe regenerating intestines localized Netrin to coelomic epithelial cells and UNC5B to differentiating epithelial cells, with CellChat analysis predicting strong epithelial-to-epithelial signaling. These findings strongly suggest that axonal guidance molecules play dual roles during intestinal regeneration: directing neural innervation in early-to-mid stages and orchestrating tissue boundary formation at later stages.