Brown B A, Nixon R A, Marotta C A
J Cell Biol. 1982 Jul;94(1):159-64. doi: 10.1083/jcb.94.1.159.
Tubulin proteins in mouse retinal ganglion cell (RGC) neurons were analyzed to determine whether they undergo posttranslational processing during axoplasmic transport. Alpha- and beta-tubulin comprised heterogeneous proteins in the primary optic pathway (optic nerve and optic tract) when examined by two-dimensional (2D) PAGE. In addition, however, alpha-tubulin exhibited regional heterogeneity when consecutive 1.1-mm segments of the optic pathway were analyzed separately. In proximal segments, alpha-tubulin consisted of two predominant proteins separable by isoelectric point and several less abundant species. In more distal segments, these predominant proteins decreased progressively and the alpha-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin was the same in all segments. After intravitreal injection of [3H]proline to mice, radiolabeled alpha- and beta-tubulin heteroproteins were conveyed together at a rate of 0.1-0.2 mm/d in the slowest phase of axoplasmic transport. At 45 d postinjection, the distribution of radiolabeled heterogeneous forms a alpha- and beta-tubulin in consecutive segments of optic pathway resembled the distribution of unlabeled proteins by 2D PAGE, indicating that regional heterogeneity of tubulin arises during axonal transport. Peptide mapping studies demonstrated that the progressive alteration of alpha-tubulin revealed by PAGE analysis cannot be explained by contamination of the alpha-tubulin region by other proteins on gels. The results are consistent with the posttranslational processing of alpha-tubulin during axoplasmic transport. These observations, along with the accompanying report (J. Cell Biol., 1982, 94:150-158), provide additional evidence that CNS axons may be regionally specialized.
对小鼠视网膜神经节细胞（RGC）神经元中的微管蛋白进行分析，以确定它们在轴浆运输过程中是否经历翻译后加工。通过二维（2D）聚丙烯酰胺凝胶电泳（PAGE）检测时，α-和β-微管蛋白在初级视路（视神经和视束）中构成异质蛋白。然而，此外，当对视路连续的1.1毫米节段分别进行分析时，α-微管蛋白表现出区域异质性。在近端节段，α-微管蛋白由两种可通过等电点分离的主要蛋白和几种含量较少的蛋白组成。在更远端的节段，这些主要蛋白逐渐减少，凝胶上的α-微管蛋白区域仅由含量较少的多种形式代表；凝胶上的β-微管蛋白区域仅由含量较少的多种形式代表；β-微管蛋白在所有节段中相同。向小鼠玻璃体内注射[3H]脯氨酸后，放射性标记的α-和β-微管蛋白异质蛋白在轴浆运输的最慢阶段以0.1 - 0.2毫米/天的速度一起运输。注射后45天，放射性标记的α-和β-微管蛋白异质形式在视路连续节段中的分布通过2D PAGE类似于未标记蛋白的分布，表明微管蛋白的区域异质性在轴突运输过程中产生。肽图谱研究表明，PAGE分析揭示的α-微管蛋白的逐渐改变不能用凝胶上其他蛋白对α-微管蛋白区域的污染来解释。结果与轴浆运输过程中α-微管蛋白的翻译后加工一致。这些观察结果以及随附的报告（《细胞生物学杂志》，1982年，94:150 - 158）提供了额外的证据，表明中枢神经系统轴突可能在区域上具有特异性。
