Macronuclear Duplication in the Ciliated Protozoan Euplotes

Abstract

The ribbon-like macronucleus of Euplotes euryslomus pinches in half amitotically at each cell division. Several hours before the actual division two lightly staining duplication bands (reorganization bands) appear at the ends of the nucleus and approach each other slowly, finally meeting near the middle. Distal to the bands, that is, in regions through which the bands have already passed, the concentration of DNA (Feulgen) and "histone" (alkaline fast green) is greater than in the central zone. These facts suggest the hypothesis that DNA-histone synthesis takes place in a sequential fashion starting at the tips of the nucleus and proceeding to the middle. That this hypothesis is correct is shown by autoradiographic and photometric observations. Tritium-labelled thymidine is incorporated only in a limited region immediately distal to the bands. The average amount of Feu]gen dye bound by the nucleus rises as the duplication bands approach each other, and is double the presynthesis value by the time the bands meet. A similar rise in the alkaline fast green dye is seen in duplicating nuclei, although no completely post-synthesis values were obtained in this study. The quantitative data are consistent with the assumption that the macronue]eus contains a number of DNA-histone "units," presumably chromosomes, each of which duplicates once and only once.No other animals display such a diversity of nuclear phenomena as the Protozoa, and consequently, this group has long held the attention of cytologists and geneticists alike. A persistent problem concerns the nature of the ciliate macronucleus which, as is well known, plays an important role in the determination of the phenotype (29) and yet divides "amitotically." The present study deals with the mechanism of macronuclear duplication in the hypotrich ciliate, Euplotes eurystomus, and gives particular attention to the synthesis of deoxyribose nucleic acid (DNA) and histone. As we shall see, amitosis in this case follows an exceedingly precise course (cf. reference 18).In common with other ciliates Enplotes possesses an inconspicuous micronucleus and all enormous, densely staining macronucleus. In this form the macronucleus is a C-or W-shaped band * Supported by funds from the National Science Foundation and the Graduate School of the University of Minnesota.

Differential Uptake of Tritiated Thymidine into Hetero- and Euchromatin in Melanoplus and Secale

“…This is particularly significant, since we know that the content in basic proteins doubles at precisely the time of DNA doubling (Alfert andBern, 1955, andBloch andGodman, 1955) and follows the pattern of DNA replication (Gall, 1959). Among the tasks that lie ahead are: (1) to determine whether the asynchrony in replication of DNA is reflected in the synthesis of basic proteins, and (2) to determine whether the DNA of heterochromatin is more or less "metabolic" than that of euchromatin.…”

“…After that, the slides were washed in running water for 2 hours, rinsed in distilled water, and finally air-dried. Such slides may be observed by placing immersion oil directly on the film (Gall, 1959).…”

Ultrastructure of the Nuclei and Intranuclear Microtubules of Paramecium aurelia

“…On the other hand in hypotrichous ciliates, both nucleolar material and condensed chromatin becomes temporarily dispersed in a reorganization band associated with the duplication of DNA (Gall, 1959;Inaba & Suganuma, 1966;Kluss, 1962). If the duplication of DNA in the macronucleus of P. aureZia took place asynchronously in different parts of the nucleus any associated morphological changes might be difficult to detect.…”

THE SYNTHESES OF TOTAL MACRONUCLEAR PROTEIN, HISTONE, AND DNA DURING THE CELL CYCLE IN EUPLOTES EURYSTOMUS

“…The positions of the two waves of synthesis are marked cytologically by the presence of the two replication bands in which DNA synthesis is localized (4,5). The series of radioautographs in labeling occurs in the nuclear region behind each band.…”