RNA synthesis and cell division in cold‐synchronized cells of Tetrahymena pyriformis

Abstract

Cells of Tetrahymena pyriformis have been cold-synchronized using a repetitive cycle of six, two-hour cold shocks (9.5"C) alternating with decreasing periods (60-30 minutes.) at 28°C. This system gives a maximum division index of 7040% occurring at 90 minutes from the end of the last synchronizing cold-treatment (EC). Examination of the division sensitivity of these cells to actinomycin D applied continuously at ten-minute intervals from EC reveals that division is essentially blocked until approximately 40 minutes past EC, after which a rapid decrease in sensitivity to the inhibitor occurs. Coinciding with this, period of high sensitivity is the occurrence of a peak of C1* uridine incorporation at 40 minutes past EC. Inhibition of this peak is correlated with an inhibition of division, whereas strong inhibition of RNA synthesis beyond 60 minutes past EC has little effect on division activity. The similarity of these findings with those of the heat-synchronized system is discussed with the suggestion that both heat-and cold-synchronizing treatments result in the synchronous resynthesis of a division-associated fraction of RNA.

EFFECTS OF DIVISION-SYNCHRONIZING HYPOXIC AND HYPERTHERMIC SHOCKS UPON TETRAHYMENA RESPIRATION AND INTRACELLULAR ATP CONCENTRATION

“…Byfield and Scherbaum (7) have shown that hyperthermic shock increases the rate of degradation (probably enzymatic) of pulse-labeled RNA . Such degradation of RNA is consistent with the concept (see references 12,13,19,21,22,24,30,31) that at approximately 40 min after the end of a temperature shock sufficient mRNA (called "division mRNA") is synthesized to template specific protein(s) (called "division protein") which will trigger the ensuing division . If so, the division mRNA is present at the end of a 40 min period between temperature shocks .…”

“…According to this approach, if the same pattern of biochemical change occurs during the synchronized division of a cell population, regardless of the type of synchronizing procedure employed, then that pattern of biochemical change is assumed likely to occur during the division of an unperturbed cell . This "alternate procedure approach" was taken by Moner and Berger who studied the temporal pattern of RNA synthesis during the division of Tetrahymena pyriformis cells synchronized in one study (19) by periodic elevations of temperature and in another study (21) by periodic reductions of temperature .…”

Quinine: Effect on Tetrahymena <i>pyriformis</i>

“…Byfield and Scherbaum proposed that 50% inhibition of cell division in heat synchronized Tetrahymena is due to blockage of DNA synthesis by hydroxyurea [11]. RNA synthesis is also required for syn chronized cell division as shown by treatment of Tetrahymena with actinomycin D [12][13][14][15]. In this instance the cells appear to be sensitive to the drug until about 50 min prior to division and treatment with actinomycin after this time has no effect.…”