Joachimiak Ewa, Pucciarelli Sandra, Barchetta Sabrina, Ballarini Patrizia, Kaczanowska Janina, Miceli Cristina
Department of Molecular, Cellular and Animal Biology, University of Camerino, Camerino 62032, v. Camerini 2, Italy.
Protist. 2007 Jan;158(1):39-50. doi: 10.1016/j.protis.2006.08.001. Epub 2006 Oct 4.
In ciliates, different microtubular structures are nucleated from diverse Microtubule Organizing Centers (MTOCs). gamma-Tubulin is a tubulin superfamily member that plays an essential role in microtubule nucleation at the MTOCs. However, little is known about mechanisms regulating the activity of gamma-tubulin on different MTOCs and during the cell cycle. In Tetrahymena thermophila, the alpha- and beta-tubulin expression is regulated mainly at the transcriptional level, and changes in the ratio of polymerized/unpolymerized tubulin dimers lead to an increase or decrease of alpha- and beta-tubulin transcription. This study deals with the characterization of gamma-tubulin in the amicronuclear ciliate Tetrahymena pyriformis. Sequence analysis revealed some specific substitutions in nucleotide-binding loops characteristic of the Tetrahymena genus and putative conserved phosphorylation sites located on the external surface of the gamma-tubulin molecule. gamma-Tubulin expression during the cell cycle, in the presence of microtubular poisons and after deciliation, was also characterized. We found that gamma-tubulin mRNA levels are correlated with basal body proliferation and gamma-tubulin nuclear localization. We also found that gamma-tubulin expression changes during anti-microtubular drugs treatment, but does not changes during reciliation. These findings suggest a relationship between the level of unpolymerized tubulin dimers and gamma-tubulin transcription.
在纤毛虫中，不同的微管结构由多种微管组织中心（MTOC）成核。γ-微管蛋白是微管蛋白超家族成员，在MTOC的微管成核过程中起关键作用。然而，关于γ-微管蛋白在不同MTOC以及细胞周期中调节其活性的机制，人们知之甚少。在嗜热四膜虫中，α-和β-微管蛋白的表达主要在转录水平受到调控，并且聚合/未聚合微管蛋白二聚体比例的变化会导致α-和β-微管蛋白转录的增加或减少。本研究探讨了无核纤毛虫梨形四膜虫中γ-微管蛋白的特征。序列分析揭示了梨形四膜虫属特有的核苷酸结合环中的一些特定替换以及位于γ-微管蛋白分子外表面的假定保守磷酸化位点。还对细胞周期中、存在微管毒物时以及去纤毛后γ-微管蛋白的表达进行了表征。我们发现γ-微管蛋白mRNA水平与基体增殖和γ-微管蛋白的核定位相关。我们还发现γ-微管蛋白的表达在抗微管药物处理期间发生变化，但在重新纤毛化过程中不发生变化。这些发现表明未聚合微管蛋白二聚体水平与γ-微管蛋白转录之间存在关联。
