Myelinating Schwann cell and major myelin-related proteins of myelin sheath

Schematic view of a myelinating Schwann cell (A), and the major myelin-related proteins of the myelin sheath (B). A myelinating Schwann cell has been “unrolled” to reveal its trapezoidal shape; the two lateral edges define the paranodes; the outside edge defines the outer mesaxon; the inside edge defines the inner mesaxon. The nodal microvilli are associated with the outermost aspect of the myelin sheath. Non-compact myelin is found in the paranodal region and in incisures. Tight junctions are depicted as two continuous lines; these form a circumferential belt and are also found in incisures. Gap junctions are depicted as ovals; these are found between the rows of tight junctions. Adherens junctions are depicted as “x”s. Schematic representation of the proteins of compact and non-compact myelin. Compact myelin contains P0, peripheral myelin protein 22 kDa (PMP22), and myelin basic protein (MBP); non-compact myelin contains E-cadherin, myelin-associated glycoprotein (MAG), DM20, Cx32, Cx29, and claudin-19. (Contributed by Dr. Steven S Scherer.)