MicroDNA, Microdeletion?; ; Extrachromosomal circular DNA (eccDNA) is widespread in eukaryotes.; ; Shibata; et al.; ; (p.; 82; , published online 8 March) have found a new form of eccDNA—microDNA—in embryonic mouse brain, heart, and liver in adult mouse brain and in mouse and human cell lines. Unlike eccDNA, which is derived from repetitive sequences, transposable elements, or viral genomes, circular microDNA is derived from nonrepetitive genomic sequences and, very often, regions associated with genes. Length profiles—at 200 to 400 base pairs long—suggest that microDNA preferentially arises from regions of DNA occupied by nucleosomes. Furthermore, microDNA has very short regions of micro-homology at the beginning and ends of the circles. Analysis of several very common microDNAs indicates that their formation seems to result in microdeletions in somatic and germline genomes.;
