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Digitale Medien

Structural and evolutionary implications of the packaging of DNA for differentiation and proliferation in the lymphocyte (1987)

Kaplan, J. G. ; Brown, D. L. ; Chaly, N. ; [weitere]

Springer

Journal of molecular evolution 26 (1987), S. 173-179

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ISSN: 1432-1432

Schlagwort(e): Lymphocytes ; B cells ; T cells ; Antigen P1 ; Topoisomerase

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary During the differentiation of the clonally distributed lymphocytes of mouse and man into mature resting B and T cells, their DNA becomes tightly packed into dense heterochromatin masses and exhibits very little transcriptional activity; it also becomes extensively nicked, containing some 3000–4000 single-strand breaks per diploid genome. The nuclear matrix is sparse and poorly organized and there are but trace amounts of the matrix-linked enzyme DNA topoisomerase II; the nucleus of these small cells is surrounded by a thin rim of cytoplasm. The resting cell can thus be considered (by analogy to a sperm cell) as a vector for transporting tightly packed and relatively inert genetic information to all parts of the body. When the lymphocyte is stimulated to enter a proliferative cycle by binding of appropriately presented antigen or mitogen to relevant membrane receptors, the cell enlarges, due to increased synthesis of protein; the dense heterochromatin is pulled out into very small clumps, as a result of an enormous growth in size as well as complexity of the nuclear matrix, and a great increase in transcriptional activity occurs. We have identified four nuclear matrix antigens that are very widely conserved in the evolution of eucaryotes and that occupy distinctive domains in interphase nuclei. Of particular interest is antigen P1, detected in organisms ranging from algae to mammals. By virtue of its location at the interface between nuclear envelope and chromatin, we propose that it plays a major and evolutionarily conserved role in chromatin organization and orientation in all eucaryotic cell types. Prior to these events, the DNA strand breaks are rejoined by a mechanism dependent on poly(ADP ribose) synthetase; rejoining of the breaks is required in order for the cells to enter the S phase of the cell cycle. Under certain experimental conditions, the induction of DNA topoisomerase II is clearly seen to precede DNA replication; topoisomerase II may be involved in some of the nuclear changes of blastogenesis. The evidence suggests that induction of single-strand breaks in DNA may be a general feature in the evolution of differentiated somatic cells. The selective advantage of the endogenously produced DNA strand breaks may be to provide an additional mechanism that prevents the differentiated cell from replicating its genome in the absence of an appropriate proliferative signal.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02099849

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Digitale Medien

The cytoskeletal microtubular system of some naked dinoflagellates (1988)

Brown, D. L. ; Cachon, J. ; Cachon, M. ; [weitere]

New York, NY : Wiley-Blackwell

Cell Motility and the Cytoskeleton 9 (1988), S. 361-374

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ISSN: 0886-1544

Schlagwort(e): microtubular cytoskeleton ; Dinoflagellates ; immunofluorescence ; Life and Medical Sciences ; Cell & Developmental Biology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Biologie , Medizin

Notizen: The cytoskeletal microtubule system has been studied in six species of unarmoured Dinoflagellates using immunofluorescence and electron microscopy. Several structures have been detected and described: (1) a subpellicular layer of microtubules, constituting the microtubular cytoskeleton, running singly or in bundles from the anterior part of the cell to the posterior; (2) a feeding apparatus, containing a ribbon of microtubules, which corresponds to a small peduncle in some species and is simply represented by a cytostome in some other species; and (3) the longitudinal flagellum that runs in a long intracytoplasmic pocket before becoming free at the extremity of the sulcus. A thorough study of the organization of the microtubular structures in a wide spectrum of Dinoflagellates is a prerequisite for understanding the evolutionary history of the group.

Zusätzliches Material: 17 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/cm.970090408

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Amino acids in a Fischer Tropsch type synthesis (1974)

Brown, D. L. ; Lawless, J. G.

In: CASI

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Publikationsdatum: 2019-06-27

Beschreibung: One postulation is described for the presence of organic compounds in meteorites which states that they were formed during the condensation of the solar nebula. A viable laboratory simulation of these conditions can be modeled after the industrial Fischer Tropsch reaction, which is known to produce organic compounds called hydrocarbons. In this simulation, a mixture of carbon monoxide, hydrogen and ammonia is heated in the presence of iron meteorite. The reaction products for amino acids, a class of organic compounds important to life, were examined. A large number of these compounds is found in meteorites and other chemical evolution experiments, but only small quantities of a few amino acids were found in the present simulation work. These results are at odds with the existing literature in which many amino acids were reported.

Schlagwort(e): SPACE BIOLOGY

Materialart: NASA-TM-X-62411 , A-5909

Format: application/pdf

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