One gap junction consists of a cluster of closely packed pairs of transmembrane channels, the connexons, through which materials of low MW diffuse from one cell to a neighboring cell. May play a role in myelination in central and peripheral nervous systems. A connexon is composed of a hexamer of connexins. Interacts with TJP1. Mainly expressed by oligodendrocytes in the central nervous system (at protein level). Expression starts after birth in the central nervous system and parallels myelination process. Mice display myelination abnormalities characterized by extracellular vacuolation along nerve fibers. Mice lacking both Gja12 and Gjb1 display a more severe demyelination phenotype associated with oligodendrocyte death. These mice develop action tremors, tonic seizures, sporadic convulsions and loss of consciousness preceding death in the sixth week after birth. Belongs to the connexin family. Gamma-type subfamily. It is uncertain whether Met-1 or Met-4 is the initiator.