Lamp brush chromosome

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"Chromatic thread, which is comparable to a bottle brush" (according to today's terminology a lamp brush chromosome) from the nucleus of an egg cell of the water salamander ( Triton ). The entire board can be seen here. O. Hertwig , 1906

Lamp brush chromosomes are temporary forms of shape and function of the chromosomes , which look like round brushes through the formation of numerous loops (loops) in the light microscope. Because of their size, they are sometimes referred to as giant chromosomes. However, this expression is also used for the differently structured polytene chromosomes .

zoology

Lampbrush chromosomes in the cell nuclei of oocytes I in newts and salamanders are particularly noticeable because they have very large genomes . The loops are formed in the ovaries of these amphibians during egg formation ( oogenesis ), namely in diplotene (part of meiotic prophase I ). The lampbrush chromosomes reveal themselves as bivalent , since two homologous partners are connected by chiasmata . The diplotene cores have a DNA content of 4 C . Lampbrush chromosomes first described Walther Flemming in oocyte nucleus of his time as Siredon pisciformis designated Axolotl . J. Rückert gave the name in 1892. Lamp brush chromosomes have also been found in the oocytes of birds, reptiles, sharks and bony fish, some mollusks and some insects.

special cases

Species of the fruit fly Drosophila unfold lamp brushes, but only on the two chromatids of the Y chromosome in spermatocytes I , i.e. in males during sperm formation ( spermatogenesis ). Among the plants, only the seaweed Acetabularia is known to have a lamp brush stage, which occurs in its single cell nucleus before gamete formation.

function

The loops unfold discontinuously from the protein-filled DNA axes of the four chromatids of each bivalent. Large amounts of RNA are transcribed from the DNA in the loops by reading RNA polymerase molecules from a starting point, close together, along a loop. The growing RNA molecules are packed with proteins and of course remain connected to their RNA polymerase and thus to the loop. Particularly in the electron microscope, it becomes clear that loops consist of one or more transcription units. The transcribing loop DNA, however, only accounts for around 2% of the total DNA in the cell nucleus. The nevertheless enormous RNA synthesis in oocytes provides the material that is necessary after fertilization to enable an embryo to grow rapidly.

Those insects that do not show lamp brushes produce the necessary material in large nutrient cells that surround the oocyte. And mammals have long pregnancies that do not require pre-treatment for the oocyte.

Chromosome structure

The lampbrush chromosomes provided fundamental insight into the organization of the chromosomes. Each chromatid contains only one, namely a continuous DNA double helix. Evidence was provided by digestion with DNase I , an enzyme that causes single-strand breaks. Such a DNA axis occupied with proteins can decondense at different points and develop temporarily transcribing loops. After the gene activity has been completed, the loops are pulled back into the axis according to the program. Similar, temporary loops are formed by the chromatids in the (transcription-active) puffs of polytene chromosomes; This is easy to see on large Balbiani rings .

Measurements of the viscoelasticity of DNA solutions confirmed that a double helix runs through an entire chromosome without being interrupted by the centromere . Drosophila americana, D. hydei, D. melanogaster and D. virilis were found to be consistent in this regard .

literature

  • Bernd Beek: Chromosomal functional structures. In: Gertrud Linnert (ed.) Cytogenetic internship. Fischer, Stuttgart / New York 1977, ISBN 3-437-20157-3 , pp. 170-185.
  • Harold Garnet Callan: Lampbrush chromosomes. Springer, Berlin 1986, ISBN 3-540-16430-8 .
  • Hans Kleinig, Peter Sitte : Cell Biology. 4th edition. Fischer, Stuttgart 1999, ISBN 3-437-26010-3 .
  • P. Quick, A. Hauck: Lamp brush chromosomes and their preparation. In: microcosm. 72, issue 2/1983, ISSN  0026-3680 , pp. 44-54.

Individual evidence

  1. ^ Rüdiger Wehner, Walter Gehring, Alfred Kühn: Zoologie . 24th edition. Georg Thieme Verlag, Stuttgart 2007, ISBN 978-3-13-772724-8 , p. 41 (online at Google Books ).
  2. ↑ Lamp brush chromosomes. In: Walther Traut: Chromosomes. Classical and Molecular Cytogenetics. Springer, Berlin / Heidelberg et al. 1991, ISBN 3-540-53319-2 , pp. 242-251.
  3. ↑ Günther F. Meyer: The functional structures of the Y chromosome in the spermatocyte nuclei of Drosophila hydei, D. neohydei, D. repleta and some other Drosophila species. In: Chromosoma. 14/1963, pp. 207-255.
  4. ↑ TJM Hulsebos, Johannes HP Hackstein, Wolfgang Hennig: Lampbrush loop-specific proteins of Drosophila hydei. In: Proceedings of the National Academy of Sciences USA. 81/1984, pp. 3404-3408.
  5. ↑ Herbert Spring, Ulrich Scheer, Werner W. Franke, Michael F. Trendelenburg: Lampbrush-type chromosomes in the primary nucleus of the green alga Acetabularia mediterranea. In: Chromosoma. 50/1975, pp. 25-43.
  6. ^ Ulrich Scheer, Werner W. Franke, Michael F. Trendelenburg, Herbert Spring: Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes. In: Journal of Cell Science. 22/1976, pp. 503-519.
  7. ^ Herbert C. Macgregor: Recent developments in the study of lampbrush chromosomes. In: Heredity. 41/1980, pp. 3-35.
  8. ↑ lampbrush chromosomes. In: Adrian T. Sumner: Chromosomes. Organization and function. Blackwell, Oxford 2003, ISBN 0-632-05407-7 , pp. 171-181.
  9. ↑ Walther Traut: Chromosomes. Classical and Molecular Cytogenetics. 1991, p. 245.
  10. ^ Adrian T. Sumner: Chromosomes. Organization and function. 2003, p. 178.
  11. ↑ Heinz Sass: RNA polymerase B in polytene chromosomes. Immunofluorescent and autoradiographic analysis during stimulated and repressed RNA synthesis. In: Cell. 28/1982, pp. 269-278.
  12. ↑ Ruth Kavenoff, Bruno H. Zimm: Chromosome-sized DNA molecules from Drosophila. In: Chromosoma. 41/1973, pp. 1-27.
  13. ↑ Lynn C. Klotz, Bruno H. Zimm: Retardation times of deoxyribonucleic acid solutions, II. Improvements in apparatus and theory. In: Macromolecules. 5/1972, pp. 471-481.