Extrachromosomal circular DNA (eccDNA) are circular DNA found in human, plant and animal cells in addition to chromosomal DNA. eccDNA originate from chromosomal DNA and can be from 50 base pairs to several mega-base pairs in length and encode regulatory elements and several full genes.
eccDNA was first discovered in 1964 by Alix Bassel and Yasuo Hoota[1] in wheat nuclei and boar sperm.[2] Since then, eccDNA has been observed in almost all organisms from plants, yeast, C. elegans, frogs, mice, chicken, birds, and humans.[3][4][5][6][7][8][9] eccDNA molecules originate in normal cells and are a by product of programmed DNA recombination events; such as V(D)J recombination.[10][9] Moreover, eccDNA production seems to be cell-type specific in somatic cells.[9]
A subtype of eccDNA, such as ecDNA, ribosomal DNA locus (Extrachromosomal rDNA circle), and double minutes have been associated with genomic instability. Double minute ecDNAs are fragments of extrachromosomal DNA, which were originally observed in a large number of human tumors including breast, lung, ovary, colon, and most notably, neuroblastoma. They are a manifestation of gene amplification during the development of tumors, which give the cells selective advantages for growth and survival. Double minutes, like actual chromosomes, are composed of chromatinand replicate in the nucleus of the cell during cell division. Unlike typical chromosomes, they are composed of circular fragments of DNA, up to only a few million base pairs in size and contain no centromere or telomere.
See also[edit]
https://en.wikipedia.org/wiki/Extrachromosomal_circular_DNA#Role_of_ecDNA_in_cancer
L-forms can be generated in the laboratory from many bacterial species that usually have cell walls, such as Bacillus subtilis or Escherichia coli. This is done by inhibiting peptidoglycan synthesis with antibiotics or treating the cells with lysozyme, an enzyme that digests cell walls. The L-forms are generated in a culture medium that is the same osmolarity as the bacterial cytosol (an isotonic solution), which prevents cell lysis by osmotic shock.[2] L-form strains can be unstable, tending to revert to the normal form of the bacteria by regrowing a cell wall, but this can be prevented by long-term culture of the cells under the same conditions that were used to produce them – letting the wall-disabling mutations to accumulate by genetic drift.[6]
Some studies have identified mutations that occur, as these strains are derived from normal bacteria.[1][2]One such point mutation D92E is in an enzyme yqiD/ispA (P54383) involved in the mevalonate pathwayof lipid metabolism that increased the frequency of L-form formation 1,000-fold.[1] The reason for this effect is not known, but it is presumed that the increase is related to this enzyme's role in making a lipid important in peptidoglycan synthesis.
Another methodology of induction relies on nanotechnology and landscape ecology. Microfluidics devices can be built in order to challenge peptidoglycan synthesis by extreme spatial confinement. After biological dispersal through a constricted (sub-micrometre scale) biological corridor connecting adjacent micro habitat patches, L-form-like cells can be derived[7] using a microfluifics-based (synthetic) ecosystem implementing an adaptive landscape[8] selecting for shape-shifting phenotypes similar to L-forms.
https://en.wikipedia.org/wiki/L-form_bacteria
https://en.wikipedia.org/wiki/Transpoviron
https://en.wikipedia.org/wiki/Extrachromosomal_DNA
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