DEVELOPMENTAL REGULATION OF POLYGLUTAMYLATED ALPHA-TUBULIN AND BETA-TUBULIN IN MOUSE-BRAIN NEURONS

Polyglutamylation is an important posttranslational modification of tu bulin that is very active in nerve cells, where it accounts for the ma in factor responsible for tubulin heterogeneity. In the present work, we have analyzed quantitative and qualitative changes in glutamylated alpha- and beta-tubulin occurring during neuronal differentiation in c ulture. Glutamylated alpha- and beta-tubulin both markedly accumulate during this process with a time course remarkably similar to that obse rved in vivo during brain development. However, the characteristics of the glutamylation of the two subunits are not exactly the same. Gluta mylated alpha-tubulin is already abundant in very young neurons and di splays, at this stage, a wide range of its degree of glutamylation (1 to 6 glutamyl units present in the lateral polyglutamyl chain), which remains unchanged during the entire period of the culture. Glutamylate d beta-tubulin is present at very low levels in young neurons and its accumulation during differentiation is accompanied by a progressive in crease in its degree of glutamylation from 2 to 6 glutamyl units. Post translational incorporation of [H-3]glutamate into alpha- and beta-tub ulin decreases during differentiation, as well as the rate of the reve rse deglutamylation reaction, suggesting that accumulation of glutamyl ated tubulin is accompanied by a decrease in the turnover of glutamyl units onto tubulin. Neuronal differentiation is also accompanied by an increase of other posttranslationally modified forms of tubulin, incl uding acetylated and non-tyrosinatable alpha-tubulin; which can occur in combination with polyglutamylation and contributes to increase the complexity of tubulin in mature neurons.