Different patterns of expression of β‐tubulin genes in Tetrahymena pyriformis during reciliation

Abstract

The ciliate Tetrahymena pyriformis contains one a-tubulin (aTT) and two p-tubulin (PTTI and PTT2) genes. The specific expression of these genes was investigated by Northern blot hybridization using oligonucleotide probes complementary to PTTI and PTT2 genes and the coding region of the a-tubulin gene. The three genes are expressed producing 1.8-kb mRNAs but the level of PTTl mRNA is much higher than that of PTT2 mRNA. During cilia regeneration, we found that the expression patterns of the aTT and pTT1 genes are similar whereas that of the PTT2 gene is different. The aTT and PTTl transcripts reached higher values between 60-120 min after the onset of reciliation than in exponentially growing cells, while pTT2 transcripts were maintained at low levels during the whole period. The differences in the amounts of steady-state populations of the both P-tubulin mRNAs do not correspond to the copy number per haploid genome. These differences could result from the fact that the promoter region of bTT2 may contain highly structured sequences which would affect the binding of the respective trans-acting factor(s).The apparent transcription rate revealed a significant increase at 15 min of reciliation which could be responsible for the high levels of aTT and PTTl transcripts in the cytoplasm between 60-120 min of reciliation. This coordinated response to cilia regeneration of the aTT and PTTI tubulin genes is also a relevant aspect of our findings.

Analyses of chromosome copy number and expression level of four genes in the ciliate Chilodonella uncinata reveal a complex pattern that suggests epigenetic regulation

“…Our quantitative PCR analyses demonstrate a further correlation between codon usage bias and expression levels: genes that are more biased sequences β-tub-SP1 and β-tub-SP2 are more highly expressed. This hypothesis is consistent with a previous study in Tetrahymena pyriformis of β-tubulin genes expression investigated by Northern blot hybridization (Soares et al, 1991). …”

“…In Tetrahymena pyriformis , the expression pattern of two different β-tubulin seems to be different during reciliation (Soares et al, 1991). In the ciliate Euplotes focardii , transcription of two γ-tubulin are different with one gene cell-cycle dependant whereas the other one is constant during life cycle but at very low levels of expression (Maziale et al, 2008).…”

Mutation accumulation in Tetrahymena

“…It is expected that differences in amplification of single copy genes will reflect differences in copy number whenever the two initial DNA concentrations are kept equal and the genes are constitutively expressed. The genes selected (Actin, alpha-tubulin, and Elongation factor 1 alpha) are all single copy genes in the haploid genome [51-53] and if located in different Mac chromosomes, each one would be an independent estimation of the level of duplication. Primers were designed with the help of Primer Express 3.0 (Applied Biosystems, Foster City, CA) in highly conserved regions between the two species so the same primer pairs could be used in the PCR amplifications and similar amplification efficiencies could be assumed.…”

Regulation and evolution of the single alpha‐tubulin gene of the ciliate Tetrahymena thermophila

“…First, three direct repeats of AATG were found between -389 and -378 relative to the first ATG. Multiple direct repeats of AATG have also been reported upstream of the alpha-tubulin gene in T. pyrijormis and the major expressed beta-tubulin gene in T. pyriformis and T. therrnophila [Soares et al, 1991;Gaertig et al, 19931. Similar occurrences of repeats of AATG did not appear in multiple random shufflings of the 1.4 kb cloned upstream region of the T. thermophila alpha-tubulin gene.…”