Plays a role in the formation of tricellular tight junctions and of epithelial barriers (PubMed:16365161, PubMed:21245199). Required for normal hearing via its role in the separation of the endolymphatic and perilymphatic spaces of the organ of Corti in the inner ear, and for normal survival of hair cells in the organ of Corti (PubMed:26677943). Interacts with TJP1. Interacts with the ubiquitin ligase ITCH. Interacts (via C-terminal cytoplasmic domain) with LSR (via the cytoplasmic domain), ILDR1 and ILDR2; the interaction is required to recruit MARVELD2 to tricellular contacts (PubMed:21245199, PubMed:23239027). Found at tricellular contacts. Detected in small intestine, stomach and kidney, in epithelial cells (PubMed:16365161). Detected in pancreas, retina and lung, and in stria vascularis, utricle and the organ of Conti in the inner ear (at protein level) (PubMed:26677943, PubMed:17186462). Predominantly detected in small intestine, lung and kidney, with lower levels in liver, testis and brain (PubMed:16365161). In colon, expressed in the entire crypts (PubMed:23239027). Phosphorylated. Ubiquitinated by ITCH; but this ubiquitination does not lead to proteasomal degradation. No visible phenotype at birth. Mutant mice have normal gait and equilibrium and are fertile. They display severe and rapidly progressing hearing loss already 14 days after birth, and completely lack response to a 90 dB sound 21 days after birth. Endocochlear potential and paracellular permeability in the stria vascularis are not affected. The arrangement of inner and outer hair cells in the organ of Corti appears normal at 12 days after birth, but outer hair cells and inner hair cells have disappeared by 21 days after birth. Hair cells survive on cochlear explants (in vitro), suggesting that hair cell degeneration is due to K(+) leakage from the endolymph to the perilymph. Belongs to the ELL/occludin family. Truncated N-terminus.