Expression patterns of tight junction associated proteins, occludin and claudins in ameloblasts during amelogenesis of mouse incisor.

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Tight junctions (TJs) function primarily as a barrier against paracellular transports between epithelial cells and are composed of TJ associated proteins, occludin (OLD) and claudins (CLDs). CLDs form a family with 24 members and show tissue or cell specific expression. Ameloblasts originated from oral epithelium form enamel, and enamel proteins and minerals are transported across the ameloblastic layer during amelogenesis. We immunohistochemically examined the distribution patterns of TJs and expression patterns of OLD and CLDs (CLD-1 to CLD-10) in the ameloblasts. Secretory ameloblasts showed OLD, CLD-1, -8 and -9 at the distal end of the cell. In mature ameloblasts, OLD, CLD-1, -6, -7, -8, -9 and -10 were shown mainly at both distal and proximal ends of the cell, regardless of ruffle-ended or smooth-ended ameloblasts. The mature ameloblasts that only proximal ends were positively stained by these OLD and CLDs were also found. These results indicate that ameloblasts drastically change the expression patterns of CLDs and the distribution patterns of TJs between secretory and mature ameloblasts, and suggest that these differences reflect the cell functions of these cell types, specifically the transports of proteins and ions for enamel formation.