While the vast majority of cellular DNA in eukaryotes is contained in long linear strands in chromosomes, we have long recognized some exceptions like mitochondrial DNA, plasmids in yeasts, and double minutes (DMs) in cancer cells where the DNA is present in extrachromosomal circles. In addition, specialized extrachromosomal circles of DNA (eccDNA) have been noted to arise from repetitive genomic sequences like telomeric DNA or rDNA. Recently eccDNA arising from unique (nonrepetitive) DNA have been discovered in normal and malignant cells, raising interesting questions about their biogenesis, function and clinical utility. Here, we review recent results and future directions of inquiry on these new forms of eccDNA.

虽然真核生物中绝大多数细胞DNA都包含在染色体的长条线性链中，但我们早就认识到一些例外，例如线粒体DNA，酵母中的质粒以及癌细胞中DNA出现在染色体外圈中的双倍（DM）。此外，已经注意到特殊的染色体外DNA环（eccDNA）是由重复的基因组序列（如端粒DNA或rDNA）引起的。最近，在正常和恶性细胞中发现了由独特的（非重复性）DNA产生的eccDNA，这引起了有关其生物发生，功能和临床实用性的有趣问题。在这里，我们回顾了关于这些新形式的eccDNA的最新结果和未来的研究方向。