Accumulation of delta 2-tubulin, a major tubulin variant that cannot be tyrosinated, in neuronal tissues and in stable microtubule assemblies.

Tubulin is the major protein component of brain tissue. It normally undergoes a cycle of tyrosination-detyrosination on the carboxy terminus of its alpha-subunit and this results in subpopulations of tyrosinated tubulin and detyrosinated tubulin. Brain tubulin preparations also contain a third major tubulin subpopulation, composed of a non-tyrosinatable variant of tubulin that lacks a carboxy-terminal glutamyl-tyrosine group on its alpha-subunit (delta 2-tubulin). Here, the abundance of delta 2-tubulin in brain tissues, its distribution in developing rat cerebellum and in a variety of cell types have been examined and compared with that of total alpha-tubulin and of tyrosinated and detyrosinated tubulin. Delta 2-tubulin accounts for approximately 35% of brain tubulin. In rat cerebellum, delta 2-tubulin appears early during neuronal differentiation and is detected only in neuronal cells. This apparent neuronal specificity of delta 2-tubulin is confirmed by examination of its distribution in cerebellar cells in primary cultures. In such cultures, neuronal cells are brightly stained with anti-delta 2-tubulin antibody while glial cells are not. Delta 2-tubulin is apparently present in neuronal growth cones. As delta 2-tubulin, detyrosinated tubulin is enriched in neuronal cells, but in contrast with delta 2-tubulin, detyrosinated tubulin is not detectable in Purkinje cells and is apparently excluded from neuronal growth cones. In a variety of cell types such as cultured fibroblasts of primary culture of bovine adrenal cortical cells, delta 2-tubulin is confined to very stable structures such as centrosomes and primary cilia. Treatment of such cells with high doses of taxol leads to the appearance of delta 2-tubulin in microtubule bundles. Delta 2-tubulin also occurs in the paracrystalline bundles of protofilamentous tubulin formed after vinblastine treatment. Delta 2-tubulin is present in sea urchin sperm flagella and it appears in sea urchin embryo cilia during development. Thus, delta 2-tubulin is apparently a marker of very long-lived microtubules. It might represent the final stage of alpha-tubulin maturation in long-lived polymers.

Heterogeneous distribution of fatty acid-binding protein in the hearts of Wistar Kyoto and spontaneously hypertensive rats.

In the present study we investigated the concentrations of cardiac cytoplasmic fatty acid-binding protein (H-FABPc) in various regions of the left and right ventricles of both Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). To this end, the ventricles of six WKY and six SHR hearts were cut in three slices, which were further dissected in one right ventricular piece and ten left ventricular pieces (five inner layer and five outer layer pieces). After homogenisation. H-FABPc was assessed using an Enzyme Linked Immuno Sorbent Assay (ELISA) of the sandwich type. It was found that, when expressed per gram wet tissue, the overall concentration of H-FABPc tended to be lower in SHR than in WKY hearts (874 +/- 53 micrograms/g and 955 +/- 51 micrograms/g, respectively; 0.1 less than P less than 0.2, means +/- S.E.M. for n = 6 animals in each group). However, due to a 30-35% higher ventricular heart mass in SHR than in WKY, the total H-FABPc content per heart turned out to be about 20% higher in SHR than in WKY rats. No concentration differences could be detected between right and left ventricles in WKY and SHR but a marked difference between the outer layer and the inner layer of the left ventricular wall was monitored in both groups. In general, the concentration in the outer layer was 5-15% higher than in the corresponding inner layer. These differences reached the level of significance (P less than 0.05) in regions close to the basis of the heart.