CHANGES IN THE MICROTUBULE PROTEINS IN THE DEVELOPING AND TRANSECTED SPINAL-CORDS OF THE BULLFROG TADPOLE - INDUCTION OF MICROTUBULE-ASSOCIATED PROTEIN 2C AND ENHANCED LEVELS OF TAU AND TUBULIN IN REGENERATINGCENTRAL AXONS

The distribution of tubulin, microtubule-associated protein 2 and Tau in the spinal cords of bullfrog tadpoles during development and after transection was studied. alpha-Tubulin or beta-tubulin immunoreactivit y was present in the axons, neuronal perikarya and dendrites, as revea led by immunocytochemistry. The axonal staining intensity of the tubul ins in the tadpoles was significantly stronger than that in the adult bullfrog. Microtubule-associated protein 2 immunoreactivity was locali zed largely to dendrites and expanded from distal to proximal dendrite s with time; a high-molecular-weight microtubule-associated protein 2 was seen on the immunoblots of cord homogenates throughout development . Taul stained mainly the axons. Two-dimensional gel immunoblotting di sclosed that the tadpole contained a greater number of isoforms of Tau than the frog. Complete transection of the spinal cords of stage IV t adpoles was followed by regeneration of the damaged cord region. The l evels of tubulin and Tau immunoreactivity in the regenerating axons of the ventral fasciculi were generally increased. Strikingly, microtubu le-associated protein 2 immunoreactivity appeared in the regenerating axons and the chromatolytic cell bodies of axotomized motor neurons, p aralleling the induction of microtubule-associated protein 2c in the r egenerating cord segment shown by immunoblotting. The chromatolytic ce ll bodies were also markedly labeled by Taul, whereas the high-molecul ar-weight microtubule-associated protein 2 diminished on the immunoblo ts, in accordance with the reduced level of staining for the dendrites . It is apparent that the changes in the cytoskeletal proteins in the regenerating axons mostly recapitulated their developmental patterns. Moreover, the data indicate a close relationship between-tubulin and m icrotubule-associated proteins in axonal growth as well as providing e vidence for similar molecular mechanisms underlying successful regener ation for central and peripheral axons.