Topographical significance of membrane skeletal component protein 4.1B in mammalian organs
The polarized architecture of epithelial cells is a fundamental determinant of cell structures and functions. Both formation and orientation of proper epithelial polarity are needed for cell–cell or cell–matrix adhesion, signal transduction and cytoskeletal interactions of multimolecular complexes at apical, lateral and basal cell membranes. These cell membrane domains are usually segregated by some junctional complexes. Recent molecular genetic studies on the anchor structure between myelin sheaths and axons have indicated the specific molecular organization for polarization of axolemma and the myelin sheaths at paranodes, termed ‘septate-like junctions’. It was also speculated that other mammalian organs may use a similar junctional system. The protein 4.1B was originally found to be localized in paranodes and juxtaparanodes of myelinated nerve fibers. Our recent immunohistochemical studies on protein 4.1B have indicated its significance for the cell–cell and/or cell–matrix adhesion in various rodent organs. The protein 4.1 family of proteins have been supposed to possess variable molecular domains relating to cell adhesion, ion balance, receptor responses and signal transduction. Therefore, more precise studies on the molecular structure and the functional domains of protein 4.1B, as well as on its changes under physiological and pathological conditions, may provide a clue for organogenesis in various mammalian organs.