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Berlin, Germany

Cathomen T.,Hannover Medical School | Sollu C.,Hannover Medical School | Sollu C.,Institute of Virology CBF
Methods in Molecular Biology | Year: 2010

The technical advances in developing artificial endonucleases, such as zinc finger nucleases (ZFNs), have opened a wide field of applications in the genome engineering arena, including the therapeutic correction of mutated genes in the human genome. Gene editing frequencies of up to 50% in human cells under non-selective conditions reveal the power of the ZFN technology. Activity and toxicity of ZFNs are determined by a number of parameters, including the specificity of DNA binding, the kinetics of dimerization of the two ZFN subunits, and the catalytic activity. In order to investigate these parameters individually, a cell-free system that models these reactions is essential. Here, we present a simple and fast method for the functional testing of ZFNs in vitro. © 2010 Springer Science+Business Media, LLC.

Cornu T.I.,Institute of Virology CBF | Cornu T.I.,Hannover Medical School | Cathomen T.,Institute of Virology CBF | Cathomen T.,Hannover Medical School
Methods in Molecular Biology | Year: 2010

The recent development of artificial zinc finger nucleases (ZFNs) for targeted genome editing has opened a broad range of possibilities in biotechnology and gene therapy. The ZFN technology allows a researcher to deliberately choose a target site in a complex genome and create appropriate nucleases to insert a DNA double-strand break (DSB) at that site. Gene editing frequencies of up to 50% in non-selected human cells attest to the power of this technology. Potential side effects of applying ZFNs include toxicity due to cleavage at off-target sites. This can be brought about by insufficient specificity of DNA binding, hence allowing ZFN activity at similar target sequences within the genome, or by activation of the ZFN nuclease domains before the nuclease is properly bound to the DNA. Here, we describe two different methods to quantify ZFN-associated toxicity: the genotoxicity assay is based on quantification of DSB repair foci induced by ZFNs whereas the cytotoxicity is based on assessing cell survival after application of ZFNs. © 2010 Springer Science+Business Media, LLC.

Osiak A.,Hannover Medical School | Osiak A.,Institute of Virology CBF | Osiak A.,Max Delbruck Center for Molecular Medicine | Radecke F.,University of Ulm | And 12 more authors.
PLoS ONE | Year: 2011

Gene knockout in murine embryonic stem cells (ESCs) has been an invaluable tool to study gene function in vitro or to generate animal models with altered phenotypes. Gene targeting using standard techniques, however, is rather inefficient and typically does not exceed frequencies of 10 -6. In consequence, the usage of complex positive/negative selection strategies to isolate targeted clones has been necessary. Here, we present a rapid single-step approach to generate a gene knockout in mouse ESCs using engineered zinc-finger nucleases (ZFNs). Upon transient expression of ZFNs, the target gene is cleaved by the designer nucleases and then repaired by non-homologous end-joining, an error-prone DNA repair process that introduces insertions/deletions at the break site and therefore leads to functional null mutations. To explore and quantify the potential of ZFNs to generate a gene knockout in pluripotent stem cells, we generated a mouse ESC line containing an X-chromosomally integrated EGFP marker gene. Applying optimized conditions, the EGFP locus was disrupted in up to 8% of ESCs after transfection of the ZFN expression vectors, thus obviating the need of selection markers to identify targeted cells, which may impede or complicate downstream applications. Both activity and ZFN-associated cytotoxicity was dependent on vector dose and the architecture of the nuclease domain. Importantly, teratoma formation assays of selected ESC clones confirmed that ZFN-treated ESCs maintained pluripotency. In conclusion, the described ZFN-based approach represents a fast strategy for generating gene knockouts in ESCs in a selection-independent fashion that should be easily transferrable to other pluripotent stem cells. © 2011 Osiak et al.

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