ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Thymidine is a NUCLEOSIDE of thymine, one of the bases of DNA. It can be taken up into a NEURON as it is developing but not into a post-mitotic (see CELL DIVISION) CELL of any kind. As such, if thymidine with a RADIOLABEL (usually tritiated thymidine—[3H]thymidine) is given to pregnant animals, it will be taken up by all of the developing neurons of every FOETUS being carried. Sacrifice of the foetuses at specific times following injection of [3H] thymidine will allow one to track the progress of developing neurons by examining AUTORADIOGRAMS of brain sections. This technique has been used successfully to study the development of brain structures (see Altman & Bayer, 1986). In adult rats the technique is not normally used, neurons being post-mitotic. However, if a VIRUS has been introduced (as a TRANSNEURONAL TRACER using, for example, ALPHA HERPES VIRUS) DNA replication will have occurred and the progress of the virus can be monitored using [3H]thymidine.
Determination
David Woolley, Adam Woolley in Practical Toxicology, 2017
Hepatocytes isolated from rats may be used in a range of assays, such as UDS, which assesses repair that takes place following damage to DNA. The extent of DNA repair is assessed through the incorporation of tritiated thymidine into the nuclei of cells exposed to the test substance. The isolated hepatocytes are allowed to attach to glass microscope slide coverslips, where they are exposed to the test substance; they are then exposed to medium containing tritiated thymidine and, after fixing and drying, to photographic emulsion. The cells are stained, and the number of grains in the nucleus is assessed microscopically. There is also a method of measurement that uses liquid scintillation counting of the activity; however, this does not allow the exclusion of cytoplasmic grains from the total counted and so is less sensitive but also less time consuming. UDS may also be examined in an ex vivo form of the test.
Basic Cell Biology
Kedar N. Prasad in Handbook of RADIOBIOLOGY, 2020
DNA is a long chain of nucleotides and therefore is referred to as a polynucleotide. Each nucleotide is composed of three compounds linked together: (1) phosphoric acid; (2) a sugar, in the form of deoxyribose; and (3) a base (Figure 2.7). Bases are divided into two classes, purine and pyrimidine. In DNA, purines are adenine (A) and guanine (G), and pyrimidines are cytosine (C) and thymine (T). Thymine is very specific for DNA structure; therefore, 3H-thymidine has been used extensively in the study of DNA synthesis. In 1953, Watson and Crick proposed a double-helix structure for DNA in which two bases are joined together by hydrogen bonds.43 A diagrammatic structure of DNA is shown in Figure 2.8. It should be noted that adenine pairs with thymine, whereas cytosine pairs with guanine. Figure 2.9 shows a schematic representation of DNA replication. During replication of each strand, the newly formed strand attaches with the proper base of the old one to form a double-stranded DNA. A new DNA strand was synthesized in vitro by using a specific enzyme polynucleotide pyrophosphorylase, precursor of DNA, and DNA from other sources. The newly formed DNA was identical to DNA that was added to the reaction mixture. This showed conclusively that DNA acts as a template for the synthesis of another strand of DNA.
Blockade of Stat3 oncogene addiction induces cellular senescence and reveals a cell-nonautonomous activity suitable for cancer immunotherapy
Published in OncoImmunology, 2020
Mara De Martino, Mercedes Tkach, Sofía Bruni, Darío Rocha, María F. Mercogliano, Mauro E. Cenciarini, María F. Chervo, Cecilia J. Proietti, Florent Dingli, Damarys Loew, Elmer A. Fernández, Patricia V. Elizalde, Eliane Piaggio, Roxana Schillaci
Splenocytes were isolated from healthy BALB/c or C57BL/6 mice and T cells were purified by negative selection using EasySep™ (Stemcell Technologies) Mouse T Cell Isolation Kit according to the manufacturer’s specifications. For activation and differentiation assay, T cells were stimulated with CD3/CD28 beads (Gibco, Thermo Fisher Scientific) for 72 h in 96-well plates using a 0.1:1 beads:lymphocyte ratio, and cells were stained with the indicated antibodies. For proliferation assay, stimulation with CD3/CD28 beads was performed for 72 h in 96-well plates using a 0.5:1 beads:lymphocyte ratio. In the last 6 h, a 0.5 μCi [3H] thymidine (NEN, DuPont; specific activity: 20 Ci/mmol) was added. The assay was performed by quadruplicate as described previously.8 In some cases, antibodies anti-CCL2, CCL5, CXCR3, IL-15, and IFNAR were added at the beginning of the experiment.
The Na/Ca Exchange as a Target for Antitumor Effect of 4Hz Pulsing Magnetic Field
Published in Electromagnetic Biology and Medicine, 2020
Yerazik Mikaelyan, Naira Eloyan, Sinerik Ayrapetyan
The number of molecules [3H]-Thymidine involving in DNA was counted. In in vitro experiments 20 mkl [3H]-Thymidine containing 0.5 ml PS with 37Bq activity was intraperitionally injected to animals. After 18 h, animals were sacrificed and the liver, spleen, and tumor tissue slices were dissected. To remove surface-adherent and extracellular tracer the liver, spleen, and tumor tissue slices were washed fivefold; duration of each one was about 5 min in normal ([3H]-Thymidine-free) PS. After determination of wet and dry weight of samples, they were homogenized in 50 µl of 68% HNO3 solution. Then 2 ml of Bray’s scintillation fluid was added and radioactivity of samples was quantified with Wallac-1450 Liquid Scintillation and Luminescence Counter (Pribori Oy, Turku, Finland). The number of [3H]-Thymidine molecules binding with cell membranes was defined per mg of dry weight of samples.
Clinical development of retroviral replicating vector Toca 511 for gene therapy of cancer
Published in Expert Opinion on Biological Therapy, 2021
Sara A. Collins, Ashish H. Shah, Derek Ostertag, Noriyuki Kasahara, Douglas J. Jolly
As noted, yeast cytosine deaminase expressed by RRV-CD catalyzes intracellular conversion of the antifungal prodrug 5-FC into the anticancer drug 5-FU. The primary mechanism of action by which 5-FU exerts its cytotoxicity is inhibition of thymidylate synthase, the key enzyme in the de novo synthesis of thymidine [59]. Lack of thymidine, the only nucleotide unique to DNA, has a profound effect on actively dividing cells, ultimately resulting in ‘thymineless death’ [60]. However, quiescent cells do not require high levels of thymidine to support DNA replication, and are able to maintain DNA repair by upregulation of the salvage pathway enzyme thymidine kinase [61]. Thus, cancer cells that were previously infected during mitosis, but which then enter quiescence, would survive prodrug treatment. In fact, 5-FU inhibition of thymidylate synthase has even been reported to drive cancer cells into quiescence to escape cell death [62,63]. These infected quiescent cancer cells represent a reservoir of virus-producing cells which continue to constitutively bud off virus progeny from the integrated provirus even in quiescence, enabling viral persistence and continued viral transmission to as yet uninfected cancer cells as they resume mitosis during tumor recurrence. Notably, long-term control of tumor growth was achieved in human xenograft tumor models in immunodeficient mice, but recurrence was still observed upon cessation of prodrug treatment [38].
Related Knowledge Centers
- Cell Synchronization
- Deoxyribose
- DNA
- Nucleoside
- Pyrimidine
- Transfer Rna
- Deoxyadenosine
- Management of HIV/AIDS
- Zidovudine
- T Arm