Cell cycle-dependent expression of gamma-tubulin in the amicronuclear ciliate Tetrahymena pyriformis

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.