Extrachromosomal circular DNAs from murine hemopoietic tissue cells

Extrachromosomal circular DNA complexes from cells of murine hemopoietic organs, bone marrow, thymus, spleen, and lymph nodes were examined by mica-press-adsorption method (H. Yamagishi, T. Kunisada, and T. Tsuda, 1982, Plasmid 8, 299-306). They showed wide size distribution, from 0.3 to 10 micron. The large-size DNAs of more than 1 micron (3.1 kb) in contour length were more abundant in bone marrow and thymus than they were in spleen and lymph nodes. The appearance of the large size DNAs was examined on splenocytes of athymic nude mice during ontogeny. The large-size DNAs first became detectable after 2 weeks of age and the amount increased thereafter until 9 weeks of age. It appears that large-size circular DNAs appear during differentiation from the hemopoietic stem cells into several descendent cells. Possible immunological implications for the appearance of extrachromosomal circular DNAs are discussed.