Extrachromosomal circular DNA

Extrachromosomal circular DNA (eccDNA) is circular DNA found in plant and animal cells, including human cells, in addition to chromosomal DNA. eccDNA originate from chromosomal DNA and can be from 50 base pairs to 5 million base pairs in length. Large eccDNA molecules have been found in the nuclei of human cancer cells and shown to carry many copies of driver oncogenes which are transcribed in tumour cells. Based on this evidence it is thought that eccDNA contributes to cancer growth. eccDNA is not to be confused with circular RNA or circRNA. Extrachromosomal circular DNA (eccDNA) is circular DNA found in plant and animal cells, including human cells, in addition to chromosomal DNA. eccDNA originate from chromosomal DNA and can be from 50 base pairs to 5 million base pairs in length. Large eccDNA molecules have been found in the nuclei of human cancer cells and shown to carry many copies of driver oncogenes which are transcribed in tumour cells. Based on this evidence it is thought that eccDNA contributes to cancer growth. eccDNA is not to be confused with circular RNA or circRNA. In mammalian cells, eccDNA was first discovered in 1972 via Caesium chloride Ethidium bromide density gradients in Jerome Vinograd's laboratory. . Since then, eccDNA has been observed in almost all organisms from plants, Yeast, Caenorhabditis elegans, frogs, mice, chicken, and humans eccDNA such as the ribosomal DNA locus (Extrachromosomal rDNA circle) and Double minutes have been associated with genomic instability. Double minute eccDNAs are fragments of extrachromosomal DNA, which have been 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. They frequently harbor amplified oncogenes and genes involved in drug resistance. Double minutes, like actual chromosomes, are composed of chromatin and 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. Although eccDNA copy number has been associated with genomic instability, a subset of eccDNA molecules originate in normal cells and are a by product of programmed DNA recombination events; such as V(D)J recombination. Moreover, eccDNA production seems to be cell-type specific in Somatic cells. eccDNAs that are 200-400 bp in size are also called microDNA.