Magnetic field-controlled gene expression in encapsulated cells.

Cell and gene therapies have an enormous range of potential applications, but as for most other therapies, dosing is a critical issue, which makes regulated gene expression a prerequisite for advanced strategies. Several inducible expression systems have been established, which mainly rely on small molecules as inducers, such as hormones or antibiotics. The application of these inducers is difficult to control and the effects on gene regulation are slow. Here we describe a novel system for induction of gene expression in encapsulated cells. This involves the modification of cells to express potential therapeutic genes under the control of a heat inducible promoter and the co-encapsulation of these cells with magnetic nanoparticles. These nanoparticles produce heat when subjected to an alternating magnetic field; the elevated temperatures in the capsules then induce gene expression. In the present study we define the parameters of such systems and provide proof-of-principle using reporter gene constructs. The fine-tuned heating of nanoparticles in the magnetic field allows regulation of gene expression from the outside over a broad range and within short time. Such a system has great potential for advancement of cell and gene therapy approaches.

Positioning of the mouse Hox gene clusters in the nuclei of developing embryos and differentiating embryoid bodies.

Expression of Hox genes located on different chromosomes is precisely regulated and synchronized during development. In order to test the hypothesis that the Hox loci might cluster in nuclear space in order to share regulatory components, we performed 3D FISH on cryosections of developing mouse embryos and differentiating embryoid bodies. We did not observe any instances of co-localization of 4 different Hox alleles. Instances of 2 different alleles touching each other were found in 20-47% of nuclei depending on the tissue. The frequency of such "kissing" events was not significantly different in cells expressing a high proportion of the Hox clusters when compared to cells expressing none or only a few Hox genes. We found that the HoxB and HoxC clusters, which are located in gene-rich regions, were involved more frequently in gene kissing in embryonic nuclei. In the case of HoxB, this observation correlated with the positioning of the corresponding chromosome towards the interior of the nucleus. Our results indicate that co-regulation of the different Hox clusters is not associated with co-localization of the loci at a single regulatory compartment and that the chromosomal context may influence the extent to which they contact each other in the nucleus.