Investigation of the changes in neuronal distribution and phosphorylation state of MAP1X during development.

Neurite outgrowth is dependent on the presence in neurites of assembled microtubules which consist of polymerized tubulin to which microtubule-associated proteins (MAPs) are bound. This study adds to previous evidence of the similarity between the high molecular weight MAPs, MAP1X, MAP1B and MAP5, and explains the different staining patterns observed by different laboratories on frozen sections, using monoclonal antibodies against each MAP. Previous studies have shown that monoclonal antibody (mAb) G10 binds to MAP1X and labels growing but not mature axons in the rat nervous system and, therefore, expression of this MAP or molecular changes in it may be important for axon growth. It has been shown that a phosphorylated form of MAP5 can be detected by SDS-PAGE in brain areas with growing axons. This study shows that there is phosphate dependency of mAbG10 binding to MAP1X which is, however, lost during brain homogenization.