Distribution of CK2, its substrate MAP1B and phosphatases in neuronal cells.

Neuronal morphogenesis depends on the organization of cytoskeletal elements among which microtubules play a very important role. The organization of microtubules is controlled by the presence of microtubule-associated proteins (MAPs), the activity of which is modulated by phosphorylation and dephosphorylation. One of these MAPs is MAP1B, which is very abundant within growing axons of developing neurons where it is found phosphorylated by several protein kinases including CK2. The expression of MAP1B is notably decreased after neuronal maturation in parallel with a change in the localization of the protein, which becomes largely concentrated in neuronal cell bodies and dendrites. Interestingly, MAP1B remains highly phosphorylated at sites targeted by protein kinase CK2 in mature neurons. We have analyzed the expression and localization of CK2 catalytic subunits along neuronal development. CK2alpha subunit appears early during development whereas CK2alpha' subunit appears within mature neurons at the time of dendrite maturation and synaptogenesis, in parallel with the change in the localization of MAP1B. CK2alpha subunit is found associated with microtubule preparations obtained from either grey matter or white matter from adult bovine brain, whereas CK2alpha' subunit is highly enriched in microtubules obtained from grey matter. These results lend support to the hypothesis that CK2alpha' subunit is concentrated in neuronal cell bodies and dendrites, where it associates with microtubules, thus contributing to the increased phosphorylation of MAP1B in this localization in mature neurons.