In the brain, the complex circuits behind our cognition largely construct themselves. In a dish or on a chip however, the normal meaningful cues are missing, and any attempts to grow predefined circuits from neurons have largely met with failure. A new technique, dubbed magnetogenetics, has now provided a way to create these neural circuits by combining magnetic manipulation with the cell’s own machinery for stabilizing new growth and extensions.

The technique works by making use of the cell’s ability to target a protein, known as Rac-GTPase, which promotes the formation and stabilization of new branches. The researchers used 500nm (0.0005mm) magnetic beads that have been modified so they can hook up to these protein machines soon after they come off the presses. They can then be magnetically acquired, and then moved to the desired locations using a precisely controlled force. In order to see what they are doing, they also attached fluorescent beacons to the beads.

Other researchers had previously tried mechanically pulling on the cells with microactuators, and while impressive growth could be obtained, fine control was impossible. Other techniques using laser tweezers to pull on subcellular transparent beads, or even the cell directly also had some successes, but the level of light power necessary to do this is typically damaging to the cells. (See: Manipulating nanoparticles with an electron tractor beam.) To grow neurons on semiconductors, adhesion molecules have typically been pre-patterned along traces for the neurons to follow. When these molecules invariably degraded over time, the neuron was left without any natural supporting structure. By using a machine that nucleates the cellular endoskeleton directly, new processes can be drawn out in a more natural way that the cell can adapt to.

In the picture above, the major dynamic skeletal component, actin, has been labelled with red fluorescent molecules, while other more permanent structures known as microtubules (MTs) fluoresce in green. If the actin is nucleated in a persistent fashion, the cell’s secondary crew, the MTs, can infiltrate the new process and make it stronger. The MTs are really the railroad infrastructure of the cell. Once the actin pioneers have laid the desired course, the MTs deliver the goods, including mitochondrial power stations, ribosome factories to build proteins on site, and all other sorts of useful spare parts.

In the body, things are a little more difficult for magnetogenetic control because you can not get up close to the cells you want to manipulate. New techniques like Magnetic Resonance Navigation have demonstrated the ability to precisely position engineered nanoparticles within blood vessels. While not quite at the level of the individual cell, for guiding and stabilizing larger axon tracts in cases of neurotrauma, or if you simply need to connect a new memory chip to your hippocampus, magnetogenetics may be just what you are looking for.

Now read: The first 3D-printed human stem cells

Research paper: doi:10.1038/nnano.2013.23 – “Subcellular control of Rac-GTPase signalling by magnetogenetic manipulation inside living cells”