Turnover of DNA and Function

Pelc, S. R.

doi:10.1038/219162a0

Cited by 106 publications

(40 citation statements)

References 21 publications

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“…Interest in this fraction increased when Bell [5] revived a suggestion first put forward by Pelc [6,7] that this rapidly labelled (or "metabolic") DNA fraction might have an informational role. In the case of primary embryonic cell cultures, as used by Bell, one of us [8] has previously shown that this is unlikely to be the case, both because of identity with nuclear DNA in all properties measured and because of the peculiar size classes of the DNA itself.…”

Section: Introductionmentioning

confidence: 99%

“Cytoplasmic” DNA from primary embryonic cell cultures is not informational

Williamson¹,

McShane²,

Grunstein³

et al. 1972

FEBS Letters

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Section: Introductionmentioning

confidence: 99%

“Cytoplasmic” DNA from primary embryonic cell cultures is not informational

Williamson¹,

McShane²,

Grunstein³

et al. 1972

FEBS Letters

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“…Thus, frustrated in their mitotic attempts, they might excrete the unnecessary DNA and return to a resting state. Alternatively, these cells could have a purpose for DNA synthesis other than mitosis (17). The DNA might be used within the cell to amplify a yet undefined function and then excreted when no longer useful.…”

Section: Andmentioning

confidence: 99%

Excretion of Deoxyribonucleic Acid by Lymphocytes Stimulated with Phytohemagglutinin or Antigen

Rogers

Boldt

Kornfeld

et al. 1972

Proc. Natl. Acad. Sci. U.S.A.

140

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When human lymphocytes are cultured in the presence of phytomitogens, 70-90% of the cells undergo blast transformation and synthesize DNA. However, less than 40% of these lymphocytes actually undergo Although phytohemagglutinin (PHA) is known to be a mitogen, the number of mitoses actually counted after addition of PHA to lymphocyte cultures is relatively small. For example, Nowell found only 10% after 18 hr of incubation with colchicine at the peak of DNA synthesis despite morphologic transformation of up to 90% of these cells (1). Such PHAtransformed lymphocytes are known to be synthesizing DNA, since they are labeled when pulsed with radioactive thymidine and studied by autoradiography. The discrepancy between many cells making DNA and few caught dividing has been attributed to asynchrony of the cultured cells (2).In PHA-stimulated lymphocyte cultures, one might expect to find a significant increase in cell number resulting from mitosis, as well as a concomitant increase in the total DNA content of the culture. The reports dealing with this question do not consistently support this expectation. Schellekens and Eijsvoogels noted that total cell number declined 17% the first day, while DNA content dropped 25%; by day 3, the cell count was still only 89% of the initial values, and the DNA content was 96% (3). Hirschhorn et al. reported a decline in DNA content during a 48-hr culture of PHA-stimulated lymphocytes to 75% of the initial value (4). Clearly, if most PHA-transformed lymphocytes in these experiments underwent mitosis, a large number of daughter cells must have died and lysed. In contrast, Loeb and Agarwal measured a PHA-induced increase in DNA to nearly twice that of unstimulated cultures by 72 hr (5). Their results could be explained if each stimulated lymphocyte underwent a single mitosis and suggest that lymphocyte cultures reported in the former papers were complicated for some reason by excessive cell lysis. However, this simple explanation is confounded by the data of Polgar and Kibrick (6). These authors report experiments in which greater than 90% of lymphocytes stimulated for 24 hr with PHA ultimately became blasts, as judged morphologically; when grown continuously in the presence of ['H]thymidine, a maximum of 63% of the total number of lymphocytes present were labeled, as revealed by autoradiography on day 5, while on day 10 only 6% of the lymphocytes were labeled, yet the number of viable cells on day 10 was 57% of the original number. Cumulative in- Quadruplicate cultures of 3.3 X 106 lymphocytes in 2 ml of medium were stimulated with 24 pg of E-PHA. On day 3, 3 pCi ['Hjthymidine (6.7 Ci/mmol) was added; at the end of a 4-hr pulse, 8 ml of minimal essential medium was added, the cultures were centrifuged at 500 X g for 5 min, the cell pellets were suspended in 2 ml of medium, and grown for up to 3 more days.On the days noted above, duplicate tubes were harvested. Culture tubes were centrifuged at 500 X g for 10 min. On one set, DNA content was determined by the diphenylamine reac...

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“…J. (1969 Pelc (1968) has suggested that dividing and non-dividing cells of eukaryotic organisms contain a species of DNA ('metabolic DNA') that turns over much more rapidly than the chromosomal DNA, and that consists of extra copies of active genes. In support of this suggestion Pel (1968) cited observations made by several authors on a wide range of animal and plant tissues.…”

mentioning

confidence: 99%