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Reverse engineering the vertebrate molecular machinery for magnetic biomineralisation

Final Report Summary - MAGNETOGENETICS (Reverse engineering the vertebrate molecular machinery for magnetic biomineralisation)

If we want to understand and influence the intricate cell-to-cell signaling that occurs in our bodies, we need to develop tools that allow us to visualize and manipulate the molecular communication remotely across entire organs. To achieve this, we need to build interfaces that translate the changing patterns of biochemical signals into a series of quantitative images that can be analyzed. Conversely, the biophysical interface should be able to convert control signals sent by physical instrumentation to the organism into molecular signals that can regulate cellular function. The methodology should also have deep tissue penetration and should be targetable to genetically defined cells subserving a specific function.

It was the overarching goal of the bioengineering project Magnetogenetics to lay the groundwork for genetically controlled biomagnetic interfaces for non-invasive readout and remote actuation with genetically controlled spatiotemporal precision and whole-organism coverage. This magnetogenetic technology has the substantial advantage over photon-dependent methods in that it can penetrate much deeper into biological tissue than light-dependent techniques such as fluorescence or optoacoustic molecular imaging and optogenetics. Furthermore, magnetogenetics can directly exert mechanical work on molecular targets. As compared with chemogenetic methods that can also reach deeper tissue, magnetogenetics additionally offers higher temporal precision.

To enable magnetogenetic technology, we pursued a two-pronged strategy that incorporates both a biomimetic approach aimed at reverse-engineering naturally occurring magnetic biomineralization, as well as a synthetic biology approach that forward-engineered pathways for transport and biomineralization of iron into mammalian cells.

In particular, we have established the teleosts zebrafish and medaka fish as new genetic vertebrate models to investigate the molecular mechanism and neuronal computation underlying light-independent magnetoreception - the ability to sense earth's magnetic field. The behavioral data obtained in the absence of visible light predict magnetic magnetoreceptor cells in line with the so-called magnetite hypothesis. Importantly, the behavioral tests we established can pick out specific magnetoreceptive fish in which labor-intense searches for magnetic candidate receptor cells can be conducted conclusively (Myklatun, Lauri+, Nat Commun).

To identify and characterize intrinsically magnetic cells from dissociated tissue, we have built a magnetic microfluidic sorting device whose performance can be fine-tuned under microscopic control and which precludes any contamination with synthetic magnetic material (Myklatun+, Sci. Rep.). Since juvenile fish are relatively transparent, neuronal activity mapping can also provide a complementary approach to identify candidate magnetoreceptor cells by connectivity tracing. To empower analogous imaging experiments that work with non-transparent adult fish, we have developed molecular contrast agents and sensors for optoacoustic imaging that have deeper penetration in tissue (Roberts+, J. Am. Chem. Soc.).

In parallel, we have bottom-up engineered genetically controlled mechanisms for iron uptake and storage in mammalian cells. We have conducted a screen of proteins involved in iron transport and have identified specific genes that lead to efficient iron uptake in mammalian cells in culture. Also, we have developed a genetically controlled system based on the expression of specific cell surface receptors that lead to the uptake of modified ferritin molecules as highly efficient biogenic magnetic nanoparticle contrast agents (Massner+, AFM). Furthermore, we have genetically expressed supramolecular protein structures that form self-assembling nanocompartments within the cells in which iron can be biomineralized. We carefully characterized this fully-genetic system with respect to its subcellular organization and iron biomineralization and optimized it while benchmarking against a semi-genetic system based on binding and delivery of biomagnetic nanoparticles (Sigmund+, Nat Commun).

In summary, we have bioengineered a platform for genetically controlled systems that can render mammalian cells responsive to magnetic fields such that cellular function can be read-out and controlled across entire live organisms. We have also established a new vertebrate model system for the functional dissection of light-independent magnetoreception that provides the opportunity to identify and understand magnetoreceptor cells that underly this still elusive sense and may also inform optimizations of engineered magnetogenetic devices.