Cell division induced by mechanical stimulation in starved Tetrahymena thermophila: cell cycle without synthesis of macronuclear DNA

Authors

  • Masaaki Iwamoto,

    1. Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-853, Japan
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    • Present address: Pacific Biomedical Research Center, University of Hawaii at Manoa, Snyder Hall 306, 2538 The Mall, Honolulu, HI 96822, USA.

  • Toshiro Sugai,

    1. Department of Materials and Biological Sciences, Ibaraki University, Mito, Ibaraki 310-8521, Japan
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  • Yasuo Nakaoka

    Corresponding author
    1. Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-853, Japan
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Corresponding author. Tel./fax: +81-6-6850-6543. nakaoka@bpe.es.osaka-u.ac.jp

Abstract

Starved Tetrahymena thermophila cells underwent synchronous cell division 2 h after a mechanical stimulation. The macronucleus showed no obvious increase in DNA content before the cell division in the starvation medium, and the DNA content was decreased after the cell division. On the other hand, when the starved cells were given nutrient-supplied medium immediately after the mechanical stimulation, cell division was delayed for 3 h. This period was almost the same as that for G1 cells in the stationary culture to first division after transfer to fresh nutrient medium. These results suggest that the mechanical stimulation induces an early division of starved cells, skipping the macronuclear S-phase with the starved cells probably becoming trapped in G1. Starved cells that had finished division soon formed mating pairs with cells of the opposite type. These observations lead us to propose that cell division in starvation conditions may be necessary to reduce macronuclear DNA content prior to the mating of T. thermophila.

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