PMID- 23271393 OWN - NLM STAT- MEDLINE DCOM- 20130301 LR - 20211021 IS - 1940-087X (Electronic) IS - 1940-087X (Linking) IP - 70 DP - 2012 Dec 13 TI - Monitoring plasmid replication in live mammalian cells over multiple generations by fluorescence microscopy. PG - e4305 LID - 4305 [pii] LID - 10.3791/4305 [doi] AB - Few naturally-occurring plasmids are maintained in mammalian cells. Among these are genomes of gamma-herpesviruses, including Epstein-Barr virus (EBV) and Kaposi's Sarcoma-associated herpesvirus (KSHV), which cause multiple human malignancies (1-3). These two genomes are replicated in a licensed manner, each using a single viral protein and cellular replication machinery, and are passed to daughter cells during cell division despite their lacking traditional centromeres (4-8). Much work has been done to characterize the replications of these plasmid genomes using methods such as Southern blotting and fluorescence in situ hybridization (FISH). These methods are limited, though. Quantitative PCR and Southern blots provide information about the average number of plasmids per cell in a population of cells. FISH is a single-cell assay that reveals both the average number and the distribution of plasmids per cell in the population of cells but is static, allowing no information about the parent or progeny of the examined cell. Here, we describe a method for visualizing plasmids in live cells. This method is based on the binding of a fluorescently tagged lactose repressor protein to multiple sites in the plasmid of interest (9). The DNA of interest is engineered to include approximately 250 tandem repeats of the lactose operator (LacO) sequence. LacO is specifically bound by the lactose repressor protein (LacI), which can be fused to a fluorescent protein. The fusion protein can either be expressed from the engineered plasmid or introduced by a retroviral vector. In this way, the DNA molecules are fluorescently tagged and therefore become visible via fluorescence microscopy. The fusion protein is blocked from binding the plasmid DNA by culturing cells in the presence of IPTG until the plasmids are ready to be viewed. This system allows the plasmids to be monitored in living cells through several generations, revealing properties of their synthesis and partitioning to daughter cells. Ideal cells are adherent, easily transfected, and have large nuclei. This technique has been used to determine that 84% of EBV-derived plasmids are synthesized each generation and 88% of the newly synthesized plasmids partition faithfully to daughter cells in HeLa cells. Pairs of these EBV plasmids were seen to be tethered to or associated with sister chromatids after their synthesis in S-phase until they were seen to separate as the sister chromatids separated in Anaphase(10). The method is currently being used to study replication of KSHV genomes in HeLa cells and SLK cells. HeLa cells are immortalized human epithelial cells, and SLK cells are immortalized human endothelial cells. Though SLK cells were originally derived from a KSHV lesion, neither the HeLa nor SLK cell line naturally harbors KSHV genomes(11). In addition to studying viral replication, this visualization technique can be used to investigate the effects of the addition, removal, or mutation of various DNA sequence elements on synthesis, localization, and partitioning of other recombinant plasmid DNAs. FAU - Norby, Kathryn AU - Norby K AD - Department of Oncology, University of Wisconsin - Madison. FAU - Chiu, Ya-Fang AU - Chiu YF FAU - Sugden, Bill AU - Sugden B LA - eng GR - CA022443/CA/NCI NIH HHS/United States GR - R01 CA133027/CA/NCI NIH HHS/United States GR - P30 CA014520/CA/NCI NIH HHS/United States GR - CA070723/CA/NCI NIH HHS/United States GR - CA133027/CA/NCI NIH HHS/United States GR - P01 CA022443/CA/NCI NIH HHS/United States GR - R01 CA070723/CA/NCI NIH HHS/United States GR - T32 CA009135/CA/NCI NIH HHS/United States GR - T32CA009135/CA/NCI NIH HHS/United States PT - Journal Article PT - Research Support, N.I.H., Extramural PT - Research Support, Non-U.S. Gov't PT - Video-Audio Media DEP - 20121213 PL - United States TA - J Vis Exp JT - Journal of visualized experiments : JoVE JID - 101313252 SB - IM MH - *DNA Replication MH - HeLa Cells MH - Herpesviridae Infections/pathology MH - Herpesvirus 8, Human/genetics MH - Humans MH - Lac Operon MH - Microscopy, Fluorescence/*methods MH - Plasmids/*chemistry/genetics/metabolism MH - Tandem Repeat Sequences PMC - PMC3573748 EDAT- 2012/12/29 06:00 MHDA- 2013/03/02 06:00 PMCR- 2013/12/13 CRDT- 2012/12/29 06:00 PHST- 2012/12/29 06:00 [entrez] PHST- 2012/12/29 06:00 [pubmed] PHST- 2013/03/02 06:00 [medline] PHST- 2013/12/13 00:00 [pmc-release] AID - 4305 [pii] AID - 10.3791/4305 [doi] PST - epublish SO - J Vis Exp. 2012 Dec 13;(70):e4305. doi: 10.3791/4305.