Heterokaryon

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Heterokaryon in fungal mitosis

A heterokaryon is a multinucleate cell that contains genetically different nuclei. Heterokaryotic and heterokaryosis are derived terms. This is a special type of syncytium. This can occur naturally, such as in the mycelium of fungi during sexual reproduction, or artificially as formed by the experimental fusion of two genetically different cells, as e.g., in hybridoma technology.

Etymology

Heterokaryon is from neo-classic Greek hetero, meaning different, and karyon, meaning kernel or in this case nucleus.[citation needed] The term was coined in 1965, independently by B. Ephrussi and M. Weiss, by H. Harris and J. F. Watkins, and by Y. Okada and F. Murayama.[citation needed]

Occurrence

Heterokaryons are found in the life cycle of yeasts, for example Saccharomyces cerevisiae, a genetic model organism. The heterokaryon stage is produced from the fusion of two haploid cells. This transient heterokaryon can produce further haploid buds, or cell nuclei can fuse and produce a diploid cell, which can then undergo mitosis.

Ciliate protozoans

The term was first used for

biochemical
properties.

True fungi

Many fungi (notably the

hyphae, although a self / non-self recognition system exists in Fungi and usually prevents fusions with non-self.[1][2]

Heterokaryosis is also common upon mating, as in Dikarya (Ascomycota and Basidiomycota). Mating requires the encounter of two haploid nuclei of compatible mating types. These nuclei do not immediately fuse, and remain haploid in a n+n state until the very onset of meiosis: this phenomenon is called delayed karyogamy. Heterokaryosis can lead to individuals that have different nuclei in different parts of their mycelium, although in ascomycetes, particularly in "Neurospora", nuclei have been shown to flow and mix throughout the mycelium.[3] In heterokaryons, the notion of individual itself becomes vague since the rule of “one genome = one individual” does not apply any more.[4] Genetic heterogeneity within an individual is indeed usually considered to be detrimental, as selfish variants may be selected for and disrupt the integrity of the individual level.[5]

Slime molds

Heterokaryosis is most common in fungi, but also occurs in

haploid individuals. When genetically divergent nuclei come together in the plasmodium form, cheaters have been shown to emerge. However, genetic homogeneity among fusing amoeboid serves to maintain the multicellular plasmodium.[6]

Artificial heterokaryon

A medical example is a heterokaryon composed of nuclei from Hurler syndrome and Hunter syndrome. Both of these diseases result in problems in mucopolysaccharide metabolism. However, a heterokaryon of nuclei from both of these diseases exhibits normal mucopolysaccharide metabolism, proving that the two syndromes affect different proteins and so can correct each other in the heterokaryon.

See also

References

  1. ^ Glass, N. L. and I. Kaneko. 2003. Fatal attraction: Nonself recognition and heterokaryon incompatibility in filamentous fungi. Eukaryotic Cell, 2:1-8
  2. PMID 28955463
    .
  3. ^ Roper, M., C. Ellison, J. W. Taylor, and N. L. Glass. 2011. Nuclear and Genome Dynamics in Multinucleate Ascomycete Fungi. Current Biology 21:R786-R793
  4. ^ King R.C., Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics. 7th ed, Oxford. p.204
  5. ^ Maynard-Smith, J. and E. Szathmary. 1995. The major transitions in evolution. Oxford University Press
  6. ^ Kuzdzal-Fick, J. J., S. A. Fox, J. E. Strassmann, and D. C. Queller. 2011. High Relatedness is Necessary and Sufficient to Maintain Multicellularity in Dictyostelium. Science 334:1548-1551

External links