Laser-guided fruit flies: Thermal control

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  • Published: Jun 1, 2014
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Laser-guided fruit flies: Thermal control

Fly by wire(less)

A male Drosophila raises a wing and ‘sings’ due to neuronal activation of song neurons. FlyMAD enables precisely aiming an infrared laser at a fly in which a warmth-sensitive ion channel was genetically introduced into previously identified neurons. Credit: Dan Bath, JFRC, HHMI

The movements and behaviour of fruit flies, genetically engineered to carry a heat-sensitive ion channel, can be controlled with a precisely aimed infrared laser. The fruit fly, Drosophila melanogaster, is widely used as a model organism for biological and biomedical research and so such puppetry should allow the species to be studied more easily than ever before.

D melanogaster represents a useful experimental system for analyzing the functions of neuronal circuits the results from which can translate to neuronal function in other organisms, perhaps even including humans. Until now, it was not possible to control their neuronal activity direclty, but what amounts to a laser-guided fly-mind control laser beam - FlyMAD* - developed by Andrew Straw and his team at the Research Institute of Molecular Pathology (IMP) in Vienna, Austria and their colleagues in the USA may have overcome this barrier.

FlyMAD, or Fly Mind Altering Device, with its inbuilt video tracking system allows the researchers to target light or to heat specific body regions within the fly's body even while the insect is in motion and to simultaneously analyse brain cell activity. Using the device the team can also observe and target regions on several flies at once. In comparison with other investigative techniques, this gives them much-improved temporal resolution and they have now demonstrated proof of principle by observing two types of neurone and how their activity changes during courtship behaviour. They provide details in the journal Nature Methods.

Infrared remote control

The relatively new area of thermogenetics involves using organisms that have been genetically modified to incorporate genes for temperature-sensitive proteins. In the case of the modified fruit fly, when infrared light impinges on a specific region, the temperature at this point is raised to 30 Celsius from ambient temperature, which alters the engineered thermo-sensitive ion channels and so infrared light. The temperature jump can then be used to induce or suppress activity in specific neuronal circuits and thus change certain aspects of the flies' behaviour in a fraction of a second.

Flies waxing lyrical

Straw and colleagues showed that FlyMAD could change normal movements in the flies reliably and reproducibly stimulating the flies to "moonwalk" or raise a single wing, or sing their courtship song when males tried to mate with a ball of wax. Taking advantage of the available temporal resolution with FlyMAD, the team was able to show that activity of one type of neurone correlates with a persistent state of courtship, whereas the other cell type was important for the action of singing.

The team will next combine the activation of flies both by light and by heat - which are possible in a single experiment using FlyMAD. This will allow the researchers to activate and repress different genetic elements in the same fly, one stimulated by light the other by heat. "FlyMAD offers the fantastic opportunity to address many of our questions. We could, for example, analyze how single neurons function in a cascade within the neuronal circuit," Straw emphasizes the potential of his work. Ultimately, new insight into the function of the fly brain can also be applied to the network of cells in the mammalian brain.

"In my own lab, we are using this technology to study the neuronal computations that a fly uses to see its world," Straw told SpectroscopyNOW. "As it buzzes around your kitchen, it has to analyse all that visual input very quickly to decide where to fly, what to avoid, and on what to land," he told us. "I’m also interested in working with other scientists to apply this technology to their own questions." *Indeed, the controlling software for FlyMAD, which runs under Linux, is open source and available from the developers or via GitHub.

Related Links

Nature Methods, 2014, online: "FlyMAD: Rapid thermogenetic control of neuronal activity in freely-walking Drosophila"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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