CHANGES OF MAP2 PHOSPHORYLATION DURING BRAIN-DEVELOPMENT

The microtubule-associated protein MAP2 is essential for development o f early neuronal morphology and maintenance of adult neuronal morpholo gy. Several splice variants exist, MAP2a-d, with a lack of MAP2a in ca t brain. MAP2 is widely used as a neuronal marker. In this study we co mpared five monoclonal antibodies (MAbs) against MAP2. They show diffe rences in the immunocytochemical distribution of MAP2 isoforms during development of the visual cortex and cerebellum of the cat, Local and temporal differences were seen with MAb AP18, an antibody directed aga inst a phosphorylation-dependent epitope near the N-terminal end. In l arge pyramidal dendrites in visual cortex, the AP18 epitope remained i n parts immunoreactive after treatment with alkaline phosphatase. Thre e MAbs, AP14, MT-01, and MT-02, recognized the central region of the M AP2b molecule, which is not present in MAP2c and 2d, and reacted with phosphorylation-independent epitopes. During the first postnatal week the immunostaining in cerebellum differed between antibodies in that s ome cellular elements in external and internal granular layers and Pur kinje cells were stained to various degrees, whereas at later stages s taining patterns were similar. At early stages, antibody MT-02 stained cell bodies and dendrites in cerebral cortex and cerebellum. With pro gressing maturation, immunoreactivity became restricted to distal part s of apical dendrites of pyramidal cells and was absent from perikarya and finer proximal dendrites in cortex. MT-02 did not stain MAP2 in c erebellum of adult animals. This study demonstrates that the immunocyt ochemical detection of MAP2 depends on modifications such as phosphory lation and conformational changes of the molecule, and that MAP2 stain ing patterns differ between MAbs. Phosphorylation and specific conform ations in the molecule may be essential for modulating function and mo lecular stability of MAP2, and monoclonal antibodies against such site s may provide tools for studying the functional role of modifications.