Functional landscape of mechanistic diversity in 27 claudin family members at tight junctions.

The diversity of epithelial paracellular barriers, essential for various biological functions, is primarily determined by the combination of 27 claudins (Cldns) that form tight junctions (TJs). However, the basis of their functional diversity remains largely unexplored. Here, we generated complete Cldn-null mouse epithelial cells to reconstitute the TJ paracellular barrier (TJ barrier) with individual Cldns. Each Cldn establishes its respective TJ barrier, either autonomously or nonautonomously, exhibiting distinct ion conductivity and selectivity. Clustering algorithms revealed a previously unidentified classification of Cldns into four main classes with well-defined subclasses, moving beyond the conventional paracellular barrier-versus-channel-forming dichotomy. Our findings, including the in vivo Cldn dynamics, provide a framework for understanding TJ barrier diversity and plasticity, offering insights into organ-specific homeostasis and guiding therapeutic strategies targeting TJ barriers in health and disease.