[Instability of plasmid DNA integrated into mammalian somatic cell genome]

The phenomenon of loosing exogenic DNA from the mammalian somatic cell genome is under investigation. It is found that foreign DNA incorporated into cell genome as a result of transfection by electrophoretion may be lost with the frequency from 1/100 up to 1/100 000 per cell division during cultivation. This effect is not dependent of the nature of cell line and vector DNA. It is actual for different cell lines: A23, human fibroblasts AG 11395, murine embryonic line F9, and for different plasmid vectors: p16, p.39, pATR4 and pcDNA3.1-Higr (WRN). Integration of pDNA into genome and the following loosing of this DNA is registered by selection markers G418 and hygromycin B resistance and gancyclovir sensibility. The presence of foreign DNA in the genome was controlled by PCR. It is found that true foreign DNA deletion from the genome takes place rather than gene expression changes. For closely linked plasmid genes deletion of both genes at once as well as loosing any one gene separately is shown. Thus, the phenomenon of selective deletion of exogenic DNA from genome has been demonstrated for different mammalian cells.