MACRONUCLEAR EVENTS IN SYNCHRONOUSLY DIVIDING TETRAHYMENA PYRIFORMIS

Abstract

The macronuclei of synchronously dividing mass cultures of Tetrahymena pyriformis (strain WH6) were examined with the electron microscope for changes during two division cycles. Samples were prepared at 30-minute intervals for a period of 81/~ hours which included the time required to induce synchrony by five heat shocks (41/~ hours). The interphase macronucleus contains peripheral, crescent-shaped nucleoli and evenly distributed chromatin bodies. Centrally located RNA bodies, composed of fibers, appear 1 to 2 hours following the initial heat shock. They are completely destroyed with ribonuclease whereas the nucleoli are only partially so. Following the third heat shock the RNA bodies move to the periphery and disintegrate; the nucleoli aggregate and form blebs which protrude into the cytoplasm where they appear to pinch off and may contribute to the cytoplasmic ribonucleic acid. Cytokinesis does not occur at this time. Instead the nuclear events are repeated during the 4th and 5th hours, even though the heat shocks are terminated at 41/~ hours. Cytokinesis takes place at about 6 hours. The second division occurs about 21/~ hours later during which all the macronuclear events noted above are repeated.

On nucleolar DNA replication in Tetrahymena pyriformis GL-8: An electron microscope autoradiographic study of heat synchronized and exponentially multiplying cells

“…No nucleolar labelling was seen in 4 of these cells ( Figure 5), whereas 5 cells showed a 2 % to 5 % labelling of nucleoli ( Figure 7). A so-called RNA-body (8,23) was observed in 2 cells (20 %). The result of these observations was that 60 % of all cells showed some nucleolar labelling ( Figure 1…”

ELECTRON-MICROSCOPIC OBSERVATION ON NUCLEAR EVENTS DURING BINARY FISSION IN <i>BLEPHARISMA WARDSI</i> (CILIATA, HETEROTRICHIDA)

“…Elimination of nucleoli from the macronucleus during binary fission was reported in Paramecium bursaria (Ehret and Powers 1955) and Tetrahymena pyriformis (Elliott et at. 1962, Elliott 1963.…”

“…Some of them, however, were on changes of the nucleoli rather than of the chromonemata (Ehret and Powers 1955, Roth and Minick 1961, Elliott et al 1962, Elliott 1963. Flickinger (1965) studied the morphology of the chromonemata throughout the cell cycle of Tetrahymena pyriformis, but he did not find any correlation between the morphological changes in the chromonemata and DNA synthesis.…”

Osmium tetroxide vapor fixation of dividing and regenerating Blepharisma

“…For many years, the study of dividing ciliates did not disclose the presence of discrete filaments in either the macro-or micronucleus (Roth, 1959;Roth and Minick, 1961;Elliot, ^ , 1962;Elliot, 1963); only the observations of Roth, and Roth and Minick indicated the possible presence of filaments associated with the amitotic macronuclear division.…”

“…In an effort to answer these questions, a number of workers have expended considerable effort. Randall and Hopkins (1962) examined regenerating and dividing Stentor and embryonic chick trachea, Ehret and DeHaller (1963) extensively studied dividing Paramecium, and Sedar and Porter (1955), Roth (1960), Elliot (1962, and Roth and Shigenaka (1964) have examined different dividing ciliates; in no case was evidence found for the division of kinetosomes. Schuster (1963), in a study of the ameba-flagellate transformation of Naegleria, has observed structures that he suggests may be prekinetosomes developing in the apparent absence of formed kinetosomes.…”