Claudin 18 (CLDN18)

CLDN18 belongs to the large claudin family of proteins, which form tight junction strands in epithelial cells.The proteins vary in their N-terminal sequences, due to the use of alternate first exons, and in the presence or absence of a C-terminal domain. Northern blot analysis of mouse tissues with exon 1-specific probes detected a transcript incorporating exon 1a only in lung, and a transcript incorporating exon 1b only in stomach. No expression was detected in any other tissue examined. Immunolocalization of mouse lung bronchus and bronchioles and of glandular stomach detected Cldn18 along cell membranes, in the cytoplasm of some cells, and in punctate spots that may have represented tight junctions. Immunoelectron microscopy of mouse embryos detected Cldn18 only at tight junctions in epithelial cells.