Accumulation of microtubule-associated protein 1A (MAP1A) in differentiating P19 embryonal carcinoma cells.

We have examined the accumulation of MAP1A in retinoic acid induced P19 embryonal carcinoma (EC) neurons. By immunofluorescent confocal microscopy, MAP1A was detected in the mitotic spindle of undifferentiated cells but was not evident in association with the interphase microtubules in most cells. By day 4 of differentiation, when neurite outgrowth was underway, MAP1A was co-localize with microtubules in all neurites but was absent from growth cones. By day 8, substantial neurite outgrowth had occurred and MAP1A was seen in all processes. At day 12, no further neurite outgrowth was evident and existing neurites were organized into fascicles. Western blotting and ELISA showed that MAP1A protein levels increased during differentiation. Peak accumulation occurred no later than day 8, coinciding with the period of neurite outgrowth, and then decreased after day 8. The results suggest that in differentiating P19 EC cells MAP1A modulates microtubule dynamics during neurite outgrowth.