• Bimodal and hysteretic expression in mammalian cells from a synthetic gene circuit.

      May, Tobias; Eccleston, Lee; Herrmann, Sabrina; Hauser, Hansjörg; Goncalves, Jorge; Wirth, Dagmar; Department of Gene Regulation and Differentiation, Helmholtz Centre for Infection Research, Braunschweig, Germany. (2008)
      In order to establish cells and organisms with predictable properties, synthetic biology makes use of controllable, synthetic genetic devices. These devices are used to replace or to interfere with natural pathways. Alternatively, they may be interlinked with endogenous pathways to create artificial networks of higher complexity. While these approaches have been already successful in prokaryotes and lower eukaryotes, the implementation of such synthetic cassettes in mammalian systems and even animals is still a major obstacle. This is mainly due to the lack of methods that reliably and efficiently transduce synthetic modules without compromising their regulation properties. To pave the way for implementation of synthetic regulation modules in mammalian systems we utilized lentiviral transduction of synthetic modules. A synthetic positive feedback loop, based on the Tetracycline regulation system was implemented in a lentiviral vector system and stably integrated in mammalian cells. This gene regulation circuit yields a bimodal expression response. Based on experimental data a mathematical model based on stochasticity was developed which matched and described the experimental findings. Modelling predicted a hysteretic expression response which was verified experimentally. Thereby supporting the idea that the system is driven by stochasticity. The results presented here highlight that the combination of three independent tools/methodologies facilitate the reliable installation of synthetic gene circuits with predictable expression characteristics in mammalian cells and organisms.
    • High efficient adenoviral-mediated VEGF and Ang-1 gene delivery into osteogenically differentiated human mesenchymal stem cells.

      Klöpper, Jonas; Lindenmaier, Werner; Fiedler, Ulrike; Mehlhorn, Alexander; Stark, G Björn; Finkenzeller, Günter; Department of Plastic and Hand Surgery, University of Freiburg Medical Center, Freiburg, Germany. (2008-01)
      Survival of ex vivo constructed tissues after transplantation is limited by insufficient oxygen and nutrient supply. Therefore, strategies aiming at improvement of neovascularization of engineered tissues are a key issue in tissue engineering applications. This in vitro study aimed at exploring the usability of osteogenically differentiated human mesenchymal stem cells (MSCs) as carriers of the angiogenic growth factor genes vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1) for therapeutic angiogenesis in bone tissue engineering. The ex vivo adenoviral vector mediated transduction into osteogenically differentiated MSCs revealed a highly efficient and long lasting expression of the transgenes. Biological activity of VEGF and Ang-1 secreted from transduced cells was confirmed by analyzing the sprouting, proliferation and apoptosis of human umbilical vein endothelial cells (HUVECs) in response to conditioned medium obtained from transduced cells. The transduced osteogenically differentiated MSCs described in this report may be suitable for inducing neovascularization in bone tissue engineering applications.
    • Retroviral vector performance in defined chromosomal Loci of modular packaging cell lines.

      Gama-Norton, L; Herrmann, S; Schucht, R; Coroadinha, A S; Löw, R; Alves, P M; Bartholomae, C C; Schmidt, M; Baum, C; Schambach, A; et al. (2010-08)
      The improvement of safety and titer of retroviral vectors produced in standard retroviral packaging cell lines is hampered because production relies on uncontrollable vector integration events. The influences of chromosomal surroundings make it difficult to dissect the performance of a specific vector from the chromosomal surroundings of the respective integration site. Taking advantage of a technology that relies on the use of packaging cell lines with predefined integration sites, we have systematically evaluated the performance of several retroviral vectors. In two previously established modular packaging cell lines (Flp293A and 293 FLEX) with single, defined chromosomal integration sites, retroviral vectors were integrated by means of Flp-mediated site-specific recombination. Vectors that are distinguished by different long terminal repeat promoters were introduced in either the sense or reverse orientation. The results show that the promoter, viral vector orientation, and integration site are the main determinants of the titer. Furthermore, we exploited the viral production systems to evaluate read-through activity. Read-through is thought to be caused by inefficient termination of vector transcription and is inherent to the nature of retroviral vectors. We assessed the frequency of transduction of sequences flanking the retroviral vectors from both integration sites. The approach presented here provides a platform for systematic design and evaluation of the efficiency and safety of retroviral vectors optimized for a given producer cell line.