Apical Cytoskeletons Help Define the Barrier Functions of Epithelial Cell Sheets in Biological Systems

Abstract

Epithelial cell sheets cover every compartment of the vertebrate body, from tiny capillaries to the entire body surface. We found that specific apical cytoskeletons are associated with the cell sheet’s apical membranes and tight junctions (TJs). Thus, we defined this set of structures as a system called the “TJ-apical complex.” These structures presumably determine the transcellular and paracellular barrier characteristics of the cell sheet, and thus its overall epithelial barrier function. We recently explored the specific function of the apical cytoskeletons in tracheal multiciliated cells. During the differentiation of these cells, the basal bodies are regularly aligned just beneath the apical membrane, which ultimately lead to cilia that beat in a coordinated manner to move the surrounding fluid. To examine the dynamic features of the basal bodies in these cells, we developed a novel high-resolution, long-term, live-imaging system. We also performed a biotheoretical analysis that revealed the role of the apical microtubules in aligning the basal bodies in the apical plane which also includes the TJs. Here we discuss the molecular composition and physiological roles of the TJ-associated apical cytoskeleton in both general and multiciliated epithelial cell sheets.