Abstract
Telomerase activity was measured at each phase of the cell cycle in synchronized tobacco (Nicotiana tabacum) BY-2 cells in suspension culture with the use of the telomeric repeat amplification protocol assay. The activity was low or undetectable at most phases of the cell cycle but showed a marked increase at early S phase. The induction of telomerase activity was not affected by the S phase blockers aphidicolin (which inhibits DNA polymerase alpha) or hydroxyurea (which inhibits ribonucleotide reductase), but it was prevented by olomoucine, an inhibitor of Cdc2/Cdk2 kinases that blocks G(1)-S cell cycle transition. These results suggest that the induction of telomerase activity is not directly coupled to DNA replication by conventional DNA polymerases, but rather is triggered by the entry of cells into S phase. Various analogs of the plant hormone auxin, including indole-3-acetic acid, alpha-naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid, potentiated the increase in telomerase activity at early S phase; the growth-inactive analog 2,3-dichlorophenoxyacetic acid, however, had no such effect. Potentiation by indole-3-acetic acid of the induction of telomerase activity was dose dependent. Together, these data indicate that telomerase activity in tobacco cells is regulated in a cell cycle-dependent manner, and that the increase in activity at S phase is specifically inducible by auxin.
Highlights
Telomeres are nucleoprotein complexes present at the ends of linear eukaryotic chromosomes that preserve chromosomal integrity and are essential for genomic stability and function
Cell Cycle Dependence of Telomerase Activity—BY-2 cells were synchronized by consecutive exposure to aphidicolin and propyzamide, after which total cell number, cell division index (Fig. 2A), DNA synthesis (Fig. 2B), and telomerase activity (Fig. 2, C and D) were monitored
Effects of Cell Cycle Blockers on Telomerase Activity—To investigate whether the increase in tobacco telomerase activity at early S phase is directly coupled with DNA replication, we examined the effects of S phase blockers on telomerase activity in synchronous BY-2 cells
Summary
Potentiation by indole-3-acetic acid of the induction of telomerase activity was dose dependent Together, these data indicate that telomerase activity in tobacco cells is regulated in a cell cycle-dependent manner, and that the increase in activity at S phase is inducible by auxin. We have shown that expression of telomerase activity in synchronized BY-2 cells is largely restricted to early S phase, indicating cell cycle-dependent regulation, and that expression. Tobacco telomerase activity was shown to be inducible by the phytohormone auxin, which promotes cell cycle progression
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