Comparison Between the Timing of Micronuclear and Macronuclear Dna Synthesis in Euplotes Eurystomus
Year: 1962
Type: article
Abstract: We previously showed (5) that in double animals of Euplotes the two separate macronuclei begin DNA synthesis simultaneously, demonstrating that the cytoplasm plays a role in initiating DNA synthesis. By studying the timing of DNA synthesis in both the micronucleus and the macronucleus, we have obtained evidence that the initiation of DNA synthesis depends not only upon cytoplasmic conditions but also upon the properties of the particular nucleus. METHODS The same strain of the ciliated protozoan Euplotes eurystomus was used as in our earlier work. DNA synthesis in the macronucleus is easily followed by observing in aeeto-carmine preparations the initiation and progress of the replication bands, which have been shown to represent waves of DNA synthesis (1, 9). The bands normally originate at the two tips of the elongated macronucleus and move towards the center, fuse, and disappear. Immediately after this, the macronucleus shortens, then elongates and divides amitotically. The determination of the doubling of micronuclear DNA was accomplished by autoradiographic studies of H3-thymidine incorporation and microspectrophotometric measurements of Feulgen-positire material. For the autoradiography, tritiated thymidine (3 c/mu, Schwarz BioResearch) was added to a rapidly proliferating culture to a final concentration of 25 #c/ml. After 10 to 30 minutes in the isotope medium, cells were withdrawn, fixed and flattened in alcohol " acetic acid (3: 1), Feulgenstained, and autoradiographed with Kodak NTB-2. The microspectrophotometric measurements were made by the two-wavelength method with a Canalco microspectrophotometer. RESULTS The generation time of Euplotes eurystomus cultured in lettuce infusion containing Aerobacter aerogenes and Tetrahymena pyriformis is about 14 hours at 24°C. The bands first appear at the tips of the macronucleus about 3 hours after cytokinesis (Table I). They meet in the middle at about 13
Source: The Journal of Cell Biology
DOI: 10.1083/jcb.13.1.175
Authors: D. M. Prescott, R. F. Kimball, R. F. Carrier
Institution: Oak Ridge National Laboratory
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2121066259