The biology and pathobiology of Schwann cells.

The most common forms of inherited demyelinating neuropathy in humans are caused by mutations in the genes encoding protein zero, peripheral myelin protein 22 kDa, and connexin32, all of which are expressed by myelinating Schwann cells and are components of the myelin sheath. The phenotype of myelinating Schwann cells depends on the maintenance of axon-Schwann cell interactions, because axonal degeneration also leads to the breakdown of the myelin sheath and dedifferentiation of the previously myelinating cells into 'denervated' Schwann cells, which are essential for axonal regeneration. Several transcription factors have been shown to play critical roles in regulating the phenotype of Schwann cells, including SCIP/tst-1/Oct-6 and Krox-20, both of which are required for the normal development of the myelinating phenotype.