The classic group of MBP isoforms (isoform 4-isoform 13) are with PLP the most abundant protein components of the myelin membrane in the CNS. They have a role in both its formation and stabilization. The non-classic group of MBP isoforms (isoform 1-isoform 3/Golli-MBPs) may preferentially have a role in the early developing brain long before myelination, maybe as components of transcriptional complexes, and may also be involved in signaling pathways in T-cells and neural cells. Differential splicing events combined to optional post-translational modifications give a wide spectrum of isomers, with each of them potentially having a specialized function. Homodimer. Additional isoforms seem to exist. In the embryo, isoform 1-isoform 3 are found in neurons within the central nervous system (primarily in pioneer neurons important in the formation of the cortex) and the peripheral nervous system. They are also expressed in the thymus, gut, lung and kidney. In the adult, isoform 1-isoform 3 are highly expressed in the brain (mainly in brain regions rich in oligodendrocytes) and spleen. Lower levels are seen in the heart, kidney and lung. Isoform 2 is also found in cells of the immune system. The isoforms missing the 134 first amino acids (isoform 4-isoform 13) are almost exclusively produced in the myelin-forming cells, the mature oligodendrocytes. The differential expression of MBP isoforms is developmentally regulated. Isoform 2 and isoform 3 are first expressed during embryonic stages (as early as at embryonic day 11.5), expression of isoform 1 is turned on shortly after birth. Expression of the isoforms missing the 134 first amino acids occurs later, presumably as the oligodendrocytes approach their terminally differentiated state. As in other animals, several charge isomers may be produced as a result of optional post-translational modifications, such as phosphorylation of serine or threonine residues, deamidation of glutamine or asparagine residues, citrullination and methylation of arginine residues. Methylated on arginine residues; decreases with the age of the animal, making MBP more cationic. Phosphorylated by TAOK2, VRK2, MAPK11, MAPK12, MAPK14 and MINK1. Proteolytically cleaved in B cell lysosomes by cathepsin CTSG which degrades the major immunogenic MBP epitope and prevents the activation of MBP-specific autoreactive T cells. Defects in Mbp are a cause of dysmyelinating diseases such as the shiverer (SHI) and myelin deficient (MLD) diseases characterized by decreased myelination in the CNS, tremors, and convulsions of progressively increasing severity leading to early death. The shiverer mice only express isoform 2, the MLD mice have a reduced amount of Mbp. Belongs to the myelin basic protein family.