The function of Ensembl gene identifier ENSG00000106404 (CLDN15, claudin 15) is as follows. Forms paracellular channels: polymerizes in tight junction strands with cation- and water-selective channels through the strands, conveying epithelial permeability in a process known as paracellular tight junction permeability (PubMed:12055082, PubMed:13129853, PubMed:31188544, PubMed:35650657, PubMed:36008380). In intestinal epithelium, allows for sodium and water fluxes from the peritoneal side to the lumen of the intestine to regulate nutrient absorption and intestinal morphogenesis (By similarity). {ECO:0000250|UniProtKB:Q9Z0S5, ECO:0000269|PubMed:12055082, ECO:0000269|PubMed:13129853, ECO:0000269|PubMed:31188544, ECO:0000269|PubMed:35650657, ECO:0000269|PubMed:36008380}.