Partial Autolysis of Macronuclear Fragments Revealed by Rapid DNA Degradation in Exconjugants of Paramecium multimicronucleatum

• Published in: Zoological Science Vol. 15; no. 6; pp. 849 - 854
• Main Authors: Hirano, Yuko, Harumoto, Terue, Hara, Jyunko, Takagi, Yoshiomi
• Format: Journal Article
• Language: English
• Published: Zoological Society of Japan 01.12.1998; UniBio Press
• Subjects: Original s
• ISSN: 0289-0003
• DOI: 10.2108/zsj.15.849

During autogamy or conjugation in Paramecium, the micronucleus undergoes prezygotic and postzygotic nuclear divisions to result in new micro- and macronuclei, while the old macronucleus breaks down into fragments. The fragments appear to remain functional for some time, as evidenced by their ability to generate an intact macronucleus, via the process called macronuclear regeneration. On the other hand, macronuclear DNA degradation must take place, as suggested by a transfer of isotope-labeled material from the fragments to the developing macronuclear anlagen. We monitored electrophoretic profiles of DNA in autogamous and exautogamous cells of P. tetraurelia at 1-day intervals for 5 days, and in conjugating and exconjugant cells of P. multimicronucleatum treated with conjugation-inducing chemicals at 1–2 hr intervals for 2 days. We failed to detect DNA degradation in P. tetraurelia, but found a prominent DNA electrophoretic smear in starving exconjugant cells of P. multimicronucleatum 33–40 hr after the initiation of conjugation. This DNA degradation was remarkable in that it occurred 10–20 hr after the appearance of macronuclear anlagen, in that it occurred suddenly and transiently, showing no trace one hour before and one hour after the smear was detected, and in that most of the macronuclear fragments persisted after the smear was detected. These results show that, during the starvation period in P. multimicronucleatum exconjugants, partial autolysis of macronuclear fragments occurs at a specific stage. We propose that this stage might be the critical point after which macronuclear fragments could not be regenerated to a functional macronucleus.