Microtubules are associated with a family of proteins called microtubule associated proteins (MAPs), which includes the protein tau and a group of proteins referred to as MAP1, MAP2, MAP3, MAP4, and MAP5. MAP2 is made up of two ~280kDa apparent molecular weight bands referred to as MAP2a and MAP2b. A third lower molecular weight form, usually called MAP2c, corresponds to a pair of protein bands running at ~70kDa on SDS-PAGE gels. All these MAP2 forms are derived from a single gene by alternate transcription, and all share a C-terminal sequence which includes either three or four microtubule-binding peptide sequences, which are very similar to those found in the related microtubule binding protein tau.
MAP2 isoforms are expressed only in neuronal cells and specifically in the perikarya and dendrites of these cells. Antibodies to MAP2 are therefore excellent markers on neuronal cells, their perikarya and neuronal dendrites. In contrast, tau is found predominantly in neuronal axons.