Claudin expression in embryonic kidney tubules

Epithelial cell layers play both a structural role to maintain biological compartments and a barrier function that keeps the external and internal environments separate. Tight junctions are localized to the apical region of epithelial cells where they regulate paracellular diffusion, block the movement of membrane proteins between the apical and basolateral cell surfaces, and play a minor role in regulating cell adhesion. Claudins are the structural and molecular building blocks of tight junctions: The tightness or leakiness of the junction is determined by which of the 20 claudin family members are present in the cell. We found that claudins exhibit overlapping expression domains within embryonic epithelial cell layers in the kidney, including the nephric duct and its derivatives, and within the condensing mesonephric mesenchyme that will form the nephrons. In adult tissues, boundaries of claudin gene expression are known to correlate with different physiological properties of the tissue, but in the embryo their functional relevance is unknown. We hypothesize that these overlapping domains of claudin expression create microenvironments that are necessary for normal development and tissue morphogenesis. This research was funded by CIHR Operating Grants to IRG and AKR.