The Distribution of Tight Junctions and Junctional Proteins in the Human Body

Abstract

In this chapter we summarize recent and more established data with respect to tight junctions (TJ) and TJ associated changes in human tissues. TJs are considered as multifunctional complexes which are involved not only in regulation of paracellular diffusion, maintenance of cell polarity but also in cell signaling and gene expression regulation. There are several -sometimes contradictory- data about TJ proteins- and genes expression in the different organs of the human body. Clearly, more research is needed to understand the functions and consequences of alterations of different TJ proteins expression in normal as well as tumor tissues in order to clarify contradictory issues. In this chapter we intend to review the immense amount of data published so far in the fi eld of TJs in different organs. For better understand- ing, we grouped the organs according to their ectodermal, endodermal or mesoder- mal origin. CLDNs have been identi fi ed as the major constituents of TJ strands. All current evidence supports a central role for CLDNs in the functions of the TJs. However, the exact stoichiometry remains unclear and little is known about the molecular mechanisms taking place during assembly and strand formation in nor- mal as well as in tumor tissues. Accordingly, the majority of data presented in this chapter consider the different CLDNs expression in normal human tissues, in pre- malignant or malignant lesions. Nevertheless, we made an effort to present data about other TJ components in different organs when available