Cultured neurons contain a variety of microtubule-associated proteins.

The non-tubulin proteins associated with microtubules (MAPs) in cultures of pure sympathetic neurons have been identified using a variety of biochemical and immunochemical methods. MAPs of cultured sympathetic neurons include proteins corresponding to brain MAP-1 (consisting of MAP-1a and MAP-1b species), MAP-2, MAP-3, tau, 4 proteins that range in molecular weight from 60,000 to 76,000, and proteins with molecular weights of 210,000, 130,000 and 32,000. Many of the MAPs are phosphorylated in situ. MAP-2 and tau of cultured sympathetic neurons differ from their counterparts of brain in electrophoretic mobility. The observed variety of MAPs in sympathetic neurons together with the differences in MAPs of brain and sympathetic neurons are discussed in terms of microtubule heterogeneity in the nervous system.