Endomitosis

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The term endomitosis is understood to mean the increase in the number of chromosomes without nuclear division . This does indeed lead to condensation of the chromosomes, i.e. an endometaphase in which the chromatids can separate, but the formation of a spindle apparatus does not occur.

The definition of the term is: The nuclear membrane is not dissolved. This creates a nucleus with multiple ( polyploid ) chromosomes . The DNA was doubled in an S phase before endomitosis , so every endomitosis results from endoreplication . The latter can also produce cell nuclei with polyploid, poorly condensed chromatin or produce conspicuous polytene chromosomes .

The following example shows all three forms of an endoreplicating cell nucleus in a normal development program of the fruit fly. In nutrient cells of the ovary of Drosophila melanogaster, it can be observed that the chromatids do not separate after the first endomitosis. The following endomitoses therefore show polytene chromosomes. However, these are resolved in further endoreplications so that a now huge cell nucleus contains polyploid, little condensed chromatin.

Endomitosis was first described in the water strider in 1939 . Endomitoses with mutated chromosomes can be observed in human cancer cells.

Endomitosis in mushrooms

In many fungi, the nucleus division also takes place without dissolving the nuclear membrane. However, it ultimately does not lead to polyploidy , but again 2 form after mitosis haploid nuclei out (It should be noted that the real fungi haplonts are, that is the greatest period of their existence exist as haploid organisms). So the result is the same as with 'conventional' mitosis without changing the core phase . Endomitosis is widespread within fungi, but cannot be assigned to a specific group. For example, there are Agaricus species ( mushrooms ) which practice endomitosis and those in which mitosis occurs with dissolution of the nuclear membrane. As a (not universally tested) guiding principle can apply: Fungi with endomitosis also cause endo meiosis .

literature

  • Eeva Therman: Chromosome behavior in cell differentiation: A field ripe for exploration? In: Genetics. 141, 1995, pp. 799-804. (genetics.org)

Individual evidence

  1. ^ Alfred Benninghoff, Detlev Drenckhahn: Anatomie. 17th edition. Volume I, ISBN 978-3-437-42342-0 , pp. 84, 85.
  2. ↑ Kimberley J. Dej, Allan C. Spradling: The endocycle controls nurse cell polytene chromosome structure during Drosophila oogenesis. In: Development. 126, 1999, pp. 293-303.
  3. ↑ Lothar Geitler: The emergence of the polyploid soma nuclei of the heteroptera through chromosome division without nuclear division. In: Chromosoma. 1, 1939, pp. 1-22.
  4. ↑ Georg Politzer: Pathology of Mitosis. Borntraeger, Berlin 1934.