A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates.[1] Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, such as metabolism. During conjugation, the macronucleus disintegrates, and a new one is formed by karyogamy of the micronuclei.

Macronuclei contain hundreds to thousands of chromosomes, each present in many copies.[2][3] There is no mechanism to precisely partition this complex genome equally during nuclear division; thus, how the cell manages to maintain a balanced genome after generations of divisions is unknown.

See also

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References

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  1. ^ Prescott, D M (June 1994). "The DNA of ciliated protozoa". Microbiological Reviews. 58 (2): 233–267. doi:10.1128/mr.58.2.233-267.1994.
  2. ^ Mochizuki K (2010-07-15). "DNA rearrangements directed by non-coding RNAs in ciliates". Wiley Interdisciplinary Reviews: RNA. 1 (3): 376–87. doi:10.1002/wrna.34. PMC 3746294. PMID 21956937.
  3. ^ Pevsner J (August 2015). Bioinformatics and Functional Genomics. John Wiley & Sons. ISBN 978-1-118-58176-6.
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Ciliate

not express its genes. The macronucleus provides the small nuclear RNA for vegetative growth. Division of the macronucleus occurs in most ciliate species

Paramecium

nuclear apparatus, consisting of a polyploid macronucleus, and one or more diploid micronuclei. The macronucleus controls non-reproductive cell functions

Paramecium caudatum

nuclei (a large macronucleus and a single compact micronucleus). As in other ciliates, individuals cannot survive without the macronucleus and cannot reproduce

Nuclear dimorphism

a macronucleus that is primarily used to control metabolism, and a micronucleus which performs reproductive functions and generates the macronucleus. The

Tetrahymena

existing at a copy number of approximately 10,000 within the macronucleus. Because the macronucleus divides amitotically during binary fission, these minichromosomes

Intramacronucleata

division of the macronucleus is accomplished during binary fission of the cell. In ciliates of this subphylum, division of the macronucleus is achieved by

Protozoa

experiments of Aufderheide in 1986. These experiments demonstrated that the macronucleus, and not the cytoplasm, is responsible for clonal aging. Additional experiments

Spirostomum

Spirostomum’s macronucleus, possessing a double membrane with perforations, is the first record of a nucleus being highly extensile. The macronucleus can initially