The National Cancer Institute and the National Human Genome Research Institute recently announced a 3-year 100-million-dollar pilot study to use large-scale resequencing of genes in human tumors to identify new cancer genes. The hope is that some of these genes can be used as drug targets for developing better therapeutics for treating cancer. Although this effort will identify new cancer genes, it could be made more efficient by preferentially resequencing genes identified as novel candidate cancer genes in animal models of cancer. Although retroviral insertional mutagenesis has proven to be an effective tool for identifying novel cancer genes in the mouse, these studies are limited by the fact that retroviral mutagenesis primarily induces hematopoietic and mammary cancer, but little else, while the majority of cancers affecting humans are solid tumors. Recently, two groups have shown that sleeping beauty (SB) transposon-based insertional mutagenesis can also identify novel candidate cancer genes in the mouse. Unlike retroviral infection, SB transposition can be controlled to mutagenize any target tissue and thus potentially induce many different kinds of cancer, including solid tumors. SB transposition in animal models of cancer could therefore greatly facilitate the identification of novel human cancer genes and the development of better cancer therapies.
"For example, this approach was addressed by Dupuy and co-workers , who were able to experimentally modify the spectrum of tumors by creating a Cre-inducible SB transposase allele (RosaSBaseLsL). With this strategy, they managed to overcome the obstacle of high embryonic lethality associated with ubiquitous SB transposase expression in the presence of the pT2/Onc2 oncogene trap [76,79], and to generate a model of germinal center B-cell lymphoma. They achieved this by activating SB transposase expression with an AidCre allele that drove Cre-mediated recombination in germinal center B-cells. "
[Show abstract][Hide abstract] ABSTRACT: Transposable elements can be viewed as natural DNA transfer vehicles that, similar to integrating viruses, are capable of efficient genomic insertion. The mobility of class II transposable elements (DNA transposons) can be controlled by conditionally providing the transposase component of the transposition reaction. Thus, a DNA of interest (be it a fluorescent marker, a small hairpin (sh)RNA expression cassette, a mutagenic gene trap or a therapeutic gene construct) cloned between the inverted repeat sequences of a transposon-based vector can be used for stable genomic insertion in a regulated and highly efficient manner. This methodological paradigm opened up a number of avenues for genome manipulations in vertebrates, including transgenesis for the generation of transgenic cells in tissue culture, the production of germline transgenic animals for basic and applied research, forward genetic screens for functional gene annotation in model species, and therapy of genetic disorders in humans. Sleeping Beauty (SB) was the first transposon shown to be capable of gene transfer in vertebrate cells, and recent results confirm that SB supports a full spectrum of genetic engineering including transgenesis, insertional mutagenesis, and therapeutic somatic gene transfer both ex vivo and in vivo. The first clinical application of the SB system will help to validate both the safety and efficacy of this approach. In this review, we describe the major transposon systems currently available (with special emphasis on SB), discuss the various parameters and considerations pertinent to their experimental use, and highlight the state of the art in transposon technology in diverse genetic applications.
Mobile DNA 12/2010; 1(1):25. DOI:10.1186/1759-8753-1-25 · 2.11 Impact Factor
"The transposability of a few transposons has been demonstrated in mammalian cells. After molecular reconstruction of Sleeping Beauty (SB) transposon,4 SB has been widely used for mammalian genetic5,6 and preclinical studies7 because of its high transposability in mammalian cells. Recently, piggyBac (PB), a transposon derived from cabbage looper moth Trichoplusia ni,8 was shown to transpose more efficiently than other transposons including Tol2 (refs. "
[Show abstract][Hide abstract] ABSTRACT: Transposons are promising systems for somatic gene integration because they can not only integrate exogenous genes efficiently, but also be delivered to a variety of organs using a range of transfection methods. piggyBac (PB) transposon has a high transposability in mammalian cells in vitro, and has been used for genetic and preclinical studies. However, the transposability of PB in mammalian somatic cells in vivo has not been demonstrated yet. Here, we demonstrated PB-mediated sustained gene expression in adult mice. We constructed PB-based plasmid DNA (pDNA) containing reporter [firefly and Gaussia luciferase (Gluc)] genes. Mice were transfected by injection of these pDNAs using a hydrodynamics-based procedure, and the conditions for high-level sustained gene expression were examined. Consequently, gene expressions were sustained over 2 months. Our results suggest that PB is useful for organ-selective somatic integration and sustained gene expression in mammals, and will contribute to basic genetic studies and gene therapies.
"Transposases mediate DNA movement in lower organisms by excising defined segments of DNA and then reinserting them at other locations in the genome, a process that can be repeated multiple times for a given segment (1,2). While transposase activity probably accounts for half of the present organization of the human genome, almost all of these sequences are pseudogenes, as unregulated DNA mobility would be deleterious to human cells, causing genome instability (1–4). "
[Show abstract][Hide abstract] ABSTRACT: Metnase is a human SET and transposase domain protein that methylates histone H3 and promotes DNA double-strand break repair. We now show that Metnase physically interacts and co-localizes with Topoisomerase IIalpha (Topo IIalpha), the key chromosome decatenating enzyme. Metnase promotes progression through decatenation and increases resistance to the Topo IIalpha inhibitors ICRF-193 and VP-16. Purified Metnase greatly enhanced Topo IIalpha decatenation of kinetoplast DNA to relaxed circular forms. Nuclear extracts containing Metnase decatenated kDNA more rapidly than those without Metnase, and neutralizing anti-sera against Metnase reversed that enhancement of decatenation. Metnase automethylates at K485, and the presence of a methyl donor blocked the enhancement of Topo IIalpha decatenation by Metnase, implying an internal regulatory inhibition. Thus, Metnase enhances Topo IIalpha decatenation, and this activity is repressed by automethylation. These results suggest that cancer cells could subvert Metnase to mediate clinically relevant resistance to Topo IIalpha inhibitors.
Nucleic Acids Research 10/2008; 36(18):5822-31. DOI:10.1093/nar/gkn560 · 9.11 Impact Factor
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