Distribution of acetylated alpha-tubulin in retina and in vitro-assembled microtubules.

We have used the mouse monoclonal antibody 6-11 B-1, specific for acetylated alpha-tubulin, to determine the distribution of acetylated alpha-tubulin in in vitro-assembled microtubules and retinal tissue. Analysis by immunoblots revealed that microtubules assembled from bovine brain extracts contain both acetylated and nonacetylated alpha-tubulin. Immunofluorescence, using 6-11 B-1 and antitubulin B-5-1-2, a monoclonal antibody specific for alpha-tubulin, demonstrated the colocalization of both alpha-tubulin species in neurons of the retina and that acetylated microtubules are relatively abundant in neurons. However, analysis at higher resolution revealed that rod photoreceptors contain spatially distinct microtubule arrays which differ in content of acetylated alpha-tubulin and differ in stability. Acetylated microtubules which composed those of the rod outer segment and connecting cilium were resistant to depolymerization in nocodazole or colchicine. In contrast, the nonacetylated microtubules which composed those of the rod-inner segment were depolymerized in nocodazole or colchicine. Therefore, these acetylated microtubules are more resistant to depolymerization than non-acetylated microtubules.