S100B belongs to the S100 family, which containing 2 EF-hand calcium-binding motifs. In humans, S100B protein is encoded by the S100P gene located at 4q16, but genes that encode other numbers of s100 family proteins are almost located at 1q21 as a cluster. S100B is glial-specific and is expressed primarily by astrocytes. Not all astrocytes express S100B. It has been shown that S100B is only expressed by a subtype of mature astrocytes that ensheath blood vessels and by NG2-expressing cells. This protein may function in neurite extension, proliferation of melanoma cells, stimulation of Ca2+ fluxes, inhibition of PKC-mediated phosphorylation, astrocytosis and axonal proliferation, and inhibition of microtubule assembly. In the developing CNS it acts as a neurotrophic factor and neuronal survival protein.