MICROTUBULE-ASSOCIATED PROTEIN-1B (MAP1B) IS PRESENT IN GLIAL-CELLS PHOSPHORYLATED DIFFERENT THAN IN NEURONS

A panel of four anti-MAP1B antibodies have been used to study the pres ence and post-translational modification of MAP1B in primary cultures of glial cells. Two antibodies (150 and 125) recognize phosphorylated epitopes whereas the other two (531 and 842) recognize non-phosphoryla ted phosphorylatable epitopes on the MAP1B molecule. Immunofluorescenc e and Western blot analysis with antibodies 531 and 842 revealed the p resence of small amounts of MAP1B-like immunoreactivity in type 1 astr ocytes and a greater content in more differentiated glial cells found in long-term cultures. By immunofluorescence, these latter cells gave positive immunostaining with antibody 125, which recognizes a phosphor ylated epitope phosphorylated by casein kinase II. Antibody 150, which reacts to a phosphorylated epitope on the MAP1B molecule, did not sho w any detectable immunoreactivity in glial cells cultures, either by i mmunofluorescence or Western blot. All four antibodies recognized hipp ocampal neurones in culture, with especially intense immunostaining in cell bodies and axons, and reacted strongly with protein present in h ippocampal neurones extracts showing an electrophoretic mobility simil ar to that of brain MAP1B. In mixed optic nerve glial cell cultures, a nti-galactocerebroside (GalC) positive cells gave also positive staini ng with antibodies 531 and 125. We propose that MAP1B is present in cu ltures of glial cells in moderate amounts and with a phosphorylation s tate different than in neurones. Thus, less differentiated glial cells , such as type 1 astrocytes, have a small amount of MAP1B, mainly in a non-phosphorylated form, which is spread diffusely in the cytoplasm a nd probably does not interact with microtubules. More differentiated g lial cells, such as oligodendrocytes, show a greater content in MAP1B which, at least in part, is phosphorylated by a casein kinase II-like activity. (C) 1994 Wiley-Liss, Inc.